CA1196379A - State of charge indicator - Google Patents
State of charge indicatorInfo
- Publication number
- CA1196379A CA1196379A CA000417594A CA417594A CA1196379A CA 1196379 A CA1196379 A CA 1196379A CA 000417594 A CA000417594 A CA 000417594A CA 417594 A CA417594 A CA 417594A CA 1196379 A CA1196379 A CA 1196379A
- Authority
- CA
- Canada
- Prior art keywords
- battery
- load
- state
- charge
- voltage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16533—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application
- G01R19/16538—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies
- G01R19/16542—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies for batteries
Abstract
ABSTRACT OF THE DISCLOSURE
A method and apparatus for producing a visual signal of the state of charge of a battery selectively connected and dis-connected from an external load. A test load is connected to the battery for a predetermined period of time to draw a current pulse from the battery when the battery is disconnected from the ex-ternal load. Simultaneously, the voltage of the battery is measured. The measured voltage is converted to a digital signal, and the digital signal is transmitted to a storage means. The stored signal is then transmitted to a visual display device.
A method and apparatus for producing a visual signal of the state of charge of a battery selectively connected and dis-connected from an external load. A test load is connected to the battery for a predetermined period of time to draw a current pulse from the battery when the battery is disconnected from the ex-ternal load. Simultaneously, the voltage of the battery is measured. The measured voltage is converted to a digital signal, and the digital signal is transmitted to a storage means. The stored signal is then transmitted to a visual display device.
Description
STATE OF CHA~GE INDIC~TO~
FIELD OF THE IN~ENTION
The inv~ntion relates -to apparatus for indicating -the state of charge of a battery or batteries, such apparatus being useful, by way of example, in electric vehicles having lead-acid batteries.
BACKGROUND PRIOR ART
In an electric vehicle o~ the type cmploying lead-acid batteries, it is desirable for the driver to have a continuous reading of the state of charge of the batteries in the vehicle.
One characteristic of lead-acid batteries is that the discharge curve of the batteries is not linear! that is, the terminal volt-age of the batteries tends to remain fairly constant during initial discharge of the bat~eries when the batteries are discharged at a constant current draw, but the voltage tends to decrease relatively rapidly as the battery approaches its fully discharged state.
Despite this characteristic of the batteries commonly used in an electric vehicle, it is necessary that the state of charge indicator provide an accurate readout of ~he charge remaining in the battery throughout the period of discharge of the battery.
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S ~IARY OF THE INVENTION
The invention provides a method of producing a visual signal of the state of charge of a battery having a non-linear battery voltage discharge curve, the method comprising the steps of selectively connecting a predetermined electrical test load to the battery for a predetermined period of time to draw a current pulse from the battery while the battery is disconnected from the external electrical load, sensing the voltage of the battery when the selected electrical test loa~ is connected to the battery terminals, and electrically processing the sensed voltage to compensate for the non-linear battery discharge curve to provide a linear visual signal of the state of charge of the battery.
The invention also provides a method for producing a visual signal of the state of charge of a battery selectively connected and disconnected from an external electrical load, the method comprising the steps of selectively connecting an electrical test load to the battery for a predetermined period of time to draw a predetermined current pulse from the battery while the battery is disconnected from the external electrical load, sensing the volta~e of the battery when the selected electrical test load is contlectecl to the battery terminals, and converting the sensed voltage to a visual si~nal of the state of charge oE the battery.
The invention also provides a method for repeatedly testing the charge of a battery which is operably connected and disconnected from an external load, the method comprisincJ the steps oc selectively connecting a selected resistance to the battery for a selected time interval to produce a predetermined pulse o~ current from the battery, sensincJ the voltage of the battery during the interval, converting the sensed voltage to a digital signal, transmitting the digital signal to a digital signal storage means at a selected time, and converting the digital signal stored in the storage means to a visible display.
The invention also provides a method of testing the state of charge of a battery, which method comprises the steps of connecting the battery to a first load, sensing how long the battery is connected to the first load, disconnecting the battery from the first load and connecting a second load to the battery after the battery has been connected to the first load for a predetermined period of time, and producing, in response to the second load being connected to the battery, a signal indicating the state of charge of the battery.
The invention also provides apparatlls for measuring the state of charge of a battery selectively connected and disconnected from an external load, the apparatus comprising an electrical test load, means for selectively connecting the electrical test load to the battery for a predetermined period of time to draw a predetermined current pulse from the battery while the battery is disconnected from the external load, means for sensing the volta~e across the battery terminals when the selected test load is connected to the battery terminals, and means for converting the voltage sensed to a visual signal of the state of charge of the battery.
The invention also provides a state of charge indicator for repeatedly testing the charge of a battery which is adapted to be alternately operably connected and disconnected from an external load, the state of charge indicator comprising means for selectively ccnnecting a selected resistance to the battery for a selected timed interval to produce a pulse of current from the battery, means for sensing the voltage of the battery during the interval, means for converting the sensed voltage to a digital signal, means for receiving and storing the digital signal, means for converting the digital signal stored in the means for receiving and storing to a visible display, and means for disconnecting the selected resistance from the battery.
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The in~ention also provides a state o~
charge indicator for testin~ the state of charge o~ a battery selectively connected to an operating load, which state o:E charge indicator comprises means for sensing if the battery is connected to the operating load timing means ~or sensing how long the battery is connected to the operating load, a test load, means Eor connecting the test load to the battery in response to indication from the load connection sensing means of disconnection of the battery from the operating load after indication from the timing means that the battery was connected to the operating load for a predetermined period of time, and means for producing in response to the test load being connected to the battery a signal indicating the state of charge of the battery.
One of the advantages of the invention is that the method and apparatus of the invention provide a functional means for producing an accurate readout of the charge remaining in the battery, and even though the discharge curve of the battery is non-linear and the voltage of the battery drops off rapidly only as the battery reaches the latter half of its discharge cycle, the state of charge indicator embodying the invention providing an accurate expression of the charge left in the battery.
Various features of the invention are set forth in the following description of a preferred embodiment, in the claims, and in the drawings.
3~9 BPIEF DESCRIPTION OF Tl-IE DRAWINGS
Fig. 1 is a schematic view of a sta-te of charge measuring device embodying the invention.
Fig. 2 is a schematic view of an electronic switch cir-cuit embodied in the state of charge measuring device shown in Fig. 1.
Fig. 3 is a schematic view of a voltage sensor and display assembly embodied in the state of charge measuring device illustrated in Fig. 1.
Fig 4 is a schematic view of a control circuit embodied in the state of charge measuring device shown in Fig. 1.
Fig.. 5 is a schematic illustration of the control circuit timing of the state of charge measuring device illustrated in Fig. 1.
Fig. 6 is a schematic illustration of a typical discharge curve of a battery of the type adapted to be measured using the state of charge measuring device of the invention.
Before describing at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrange-ment of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways.
Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.
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~ PR~FERRED_EMBODIMENT
Illustrated in Fig. 1 is a state of charge indicator 10 embodying the present invention and adapted to produce a visual signal indicating the state o.E charge of the battery 12 or a bank of batteries which can be, for purposes of example, batteries of the type used in e~ectric vehicles. In the illustrated arrangement the battery 12 is electrically connected to an external load 14. In the case of an electric vehicle the external load 14 would include the electric motor of the vehicle. The means for electrically connecting the battery 12 to the external load 14 includes an accelerator switch 16 adapted to be closed when the accelerator pedal (not shown) of the vehicle is depressed and also adapted to be opened when the accelerator pedal is released.
While the state of charge indicator 10 described will be referred to, for purposes of example, in connection with an electric vehicle, it will be understood that the state of charge indicator 10 will have a variety of other uses and will be useful as a battery charge indicator in a number of other applications.
The state of charge indicator 10 shown in Fig. 1 includes an electrical test load 18 and means for selectively connecting the battery 12 to the test load 18 for a very brief period when the accelerator switch 16 has first been closed for a first predetermined length of time and when the accelerator switch 16 has subsequently been opened for a second predetermined length of time. The test load 18 comprises a resistance which produces a current pulse of relatively large magnitude :Erom the battery 12, the magnitude of the current drawn by the test load 18 being intended to be approximately the same as the average current drawn by the external -; -7 3~79 load 14. The means for selectively connecting the battery 12 to the test load 18 also includes an electronic switch means 20 adapted to selectively connect the test load 18 to the battery 12 and to then disconnect the test load lS from the bat~ery 12 after -the passage of a short time interval. The means for selectively con~
necting also includes a control circuit means 22 for selectively causing the electronic switch means 20 to connect the test load 18 to the battery 12.
Means are further provided for sensing the voltage across the terminals of the battery 12 during the period when the battery 12 is connected to the test load 18. In the arrangement illustrated in Fig. 1, this sensing means includes a voltage sensor and converter 24 to be described in greater detail hereinafter. ~eans are also provided for converting the sensed voltage to a visual signal of the state of charge of the battery. In the illustrated arrangement this means includes a digital storage device 26 and a display device 28. During the period when the electronic switch means 20 connects the battery 12 to the test load 13, the voltage sensor and converter 24 converts the sensed voltage to a plurality of digital signals.
These digital signals are then selectively transmitted from the voltage sensor converter 24 to the digital storage device 26 and the digital storage device 26, in turn, transmits the digital signals to the display device 23.
Referring now mor,e specifically to the control circuit means 22, in the illustrated arrangement the control circuit means is provided with means for selectively causing the electronic switch 20 to connect the battery 12 to the test load 13 when the accelerator switch has first been closed for at least approximately 5 seconds and then has been opened for a second selected time period, such as 3/4 of a second. By first requiring the battery 12 to be loaded for at least 5 seconds before the voltage sensor and converter 24 sense the voltage of the battery, the system prevents any erroneous readings of the terminal voltage o,F the battery which might otherwise occur due to the affects of battery recovery during long rest neriods.
For example, if the battery 12 is allowed to rest for an extended period of time, the voltage of the battery may return to an arti-ficially high level and an ini~:ial sample of the terminal voltage of the battery 12 could show the battery to be fully charged.
However, if the battery is discharged or connected to a load, the battery will quickly lose this high voltage level and return to a voltage level more nearly approximating that measured before the battery is allowed to rest.
The control circuit means 22 also includes means for trans-mitting a signal to the digital storage device 26 and to cause the delay of approxi~ately 0.5 seconds after the voltage has first been sensed by the voltage sensor and converter 24 before the signals from the voltage sensor and converter 24 can be received by the digital storage device 26.
The control circuit 22 further includes means for trans-mitting a signal to the electronic switch means 20 causing the elec-tronic switch means 22 to disconnect the test load 18 from the battery 12 after the signals from the voltage sensor and converter 24 have been transmitted to the digital storage means 26 and also received by the digital display device 28.
Referring now more particularly to the means for converting the sensed voltage to a visual signal, while the display device 2S
could have various constructions, in a preferred from of the invention it can include a plurality of light emitting diodes arranged linearly and which will be described more particularly hereinafter. The light emitting diodes are electrically connected to the digital storage 7~
means 26 such that when the battery 12 is fully char~edthe digital signal~ transmitted to each of the diodes ca~ses them to be illuminated, and then as the state of charge of the batte~y 12 is decreased, the signals to succeeding ones of the light emitting diodes are changed such that a decreasing number of diodes are illuminated. In the illustrated arrangement the display device includes 8 light emitting diodes, out it will be understood that in other arrangements other types of display devices could be used.
Figs. ~-4 illustrate more particularly one arrangement of electrical components and circuits which function to produce the results described above. Before describing in detail the specific apparatus illustrated in Figs. 2-4, it should be understood that the functions of the control circuit 22, the voltage sensor and converter 24, and the digital storage device 28 could be implemented with a microprocessor with a minimum number of support components ~dditionally, if the state of charge indicator is included in a vehicle having an on-board computer, many of these functions could be conveniently embodied in such a computer with a resulting substantial savings in cost of components. Furthermore, while in the following description the various components are described as being used in connection with testing the state of charge of a 12 volt battery adapted to produce a current of 25 amps, it will be understood that the illustrated apparatus could be conveniently modified for use in measuring the state of charge of batteries adapted to produce larger or smaller currents. For example, the state of charge indicator l~ could be conveniently modified so as to be useful in conventional electric vehicles of the type which commonly employ batteries adapted to generate 75 amperes.
Fig. 2. is a schematic view of the electonic components which preferably make up the electronic switch means or switch 20 daigramatically shown in Fig. 1 and also showing the test load 18 as comprising a resister electrically connected to the compenents of the electronic swithc 20.
Various electronic switch means arragements are possible. In the preferred embodiment illustrated in Fig. 2, such switch means comprises a thyristor or SCR 30 which is triggered to selectively connect the test load 18 to the battery 12 to draw a relatively large predetermined current pulse from the battery 12, while the battery is disconnected from theexternal load 14.
The electonic switch 20 includes anothet SCR 34 connected in circuit with a resister 36 and capacitor 38 as illustratred to form a commutating circuit, i.e., triggering SCR
34 turns off SCR 30, and vice versa. Resistoers 40 and 42 are connected to driver transistors 44 and 46, which in tunr are connected to provide trigger pulses to SCRs 30 and 34, respectively, subject to trigger outputs from the control circuit means 22, as will be described further below. A
voltage regulator 48, is connectd to the battery to provide a 5 volt positive supply as shwon.
Two fuses 50 and 52, respectively, are connected as shown. Fuse 50 preferably should be a fast acting fuse that will blow if any current above IT (load current during test), flows in the circuit. Fuse 52 prefeably should be a slower acting breaker (about one second before blowing) that will blow if a current of about IT/2 flfows in the circuit for anb extendied period of time. This protects the compinents in the event that the SCR 30 gets "stuck" on or the control circuit malflunctions.
A Euse out indicator, made up oE a resistor 54 connected to a switched 12 volt supply and to an LED 56, in turn connected to a grounded resistor 58, is also provided.
The design of the commutating circuit will be se~
forth more specifically below. For purposes of discussion, tne commutating resistor 36 has a value equal to Rc ~ the test load resistor 18 has a value equal to R1 and the saturation voltage of SCR 30 has a value equal to VscRsat. E is battery voltage. - .
IT = current through the test load 18 during the test interval.
RL is chosen first.
It is known E ~ VSCRSat. T L
so RL = E ~ VSCRSat.
IT ~1) C (the capacitance of capacitor 38) must be large enough to keep SCR 30 reverse biased through its entire turnoff time, Toff ' Toff ~ RLC
or C = Toff RL (2) Given the conduction time, TC ~ of SCR 30, the resistance RC 20 may be found.
TC = RC
or Rc = TC
C (3) TC should be made large enough so that RC is large and the current drain oE IRC is not substantial. TC is fixed at approximately 0.5 seconds by the control clrcuit 22.
A safety factor of 2 will be incorpora~ed into equations (2) and (3) giving C = 2Toff RL (2a) andRC = TC
2C (3a) In the illustrated embodiment, testing was done on a 12 volt battery of the type rated to produce a current of 25 amperes. Accordingly, the commutating circuit was designed for E=12 volts and I=25 amperes.
The SCRs used were General Electric C122s.
The saturation voltage of the SCRs was found to be approximately 2.5 volts at 25 amps. The turn off time was estimated to be 80 microseconds.
Using these values, RL, and RC and C were calculated.
RL = 0.38 Ohms (made from Nichrome wire) RC = 532 Ohms (470 Ohms was used) C = 421 Micro Farads (a Micro Farad was used in the circuit) The above discussion of design demonstrates one of the advantages of this invention. The state of charge indicator can be made to work with a variety of batteries by simply changing the values of RL, Rc and C.
A further descriptioa of the electronic switch ~0 will be given in the detailed description of operation section aEter description of the schematic circuit arrangements shown in Figs. 3 and 4.
Fig. 3 is a schematic view of the voltage sensor and converter 24, the digital storage means 26, and the display device 28. Various voltage sensor and display means arrangements are possible. In the preferred embodiment illustrated in Fig. 3, the voltage sensor and converter 24 comprises a logarithmic LED bar graph driver, the digitai storage means 26 is comprised of a pair of Quad D flip-flops, and the display device 28 comprises an 8 LED bar graph display, all connected as illustrated. As shown, the digital storage means or flip-flops 26 are connected to an unswitched 5 volt supply provided by voltage regulator 48 (Fig. 2). The 5 volt supply is unswitched so that the state of charge is retained when other switched components are turned off. The digital storage clock inputs tcLK) are connected to the sample latch output of the control circuit 22 as shown and further described below. Noise filter capacitors 60 are connected to the unswitched 5 volt supply and the flip-flops 26 as shown. In addition, inverter/drivers 61 are connected between the outputs of the flip-flops 26 and the LED bar graph display 28 as shown. The anodes of the eight LEDs, numbered 1 through 8, of the bar graph display are connected through resistor 62 to a switched 5 volt supply provided by the voltage regulator 48. A
protective diode 64 is connected between the anodes and ground to limit reverse voltage spikes across the LEDs. The voltage sensor and converter 24 is connected to the positive battery terminal or battery voltage to be sampled via potentiometer 66. In addition, a potentiometer 68 is connected to ~19~3~9 driver 24 to allow for calibration of the s-tate of charge indicator 10 as will be further described in the detailed description of operation section below~
Fig. 4 is a schematic view o~ the control circuit m e ans 22, as diagramatically shown in Fig. 1. I~hile various control circuit means arrangements are possible, in the preferred embodiment illustra-ted in Fig. 4, such means comprises a di~,ital logic circuit including NAND or NOR gates (not separately labelled), our dual JK master slave flip-flops 70 with set and reset, model 4027, an oscillator, generally designated 72, and made u~ of three inverter/d~ivers 74, a capacitor 76 and two resistors 78, and a counter ~O made up of two decade converter/drivers ~2 with 10 decade outputs, model 4017, all connected as shown. An inverter/driver 84 is connected to the Q9 output of counter 80 and an inverter/driver ~6 is connected at the accelerator input as shown.
Ihe digital logic and,o-ther components which have been described Qnd which make up the state of charge indicator 10 can be made up of separately available commercial components, having generic model numbers as designated below. Such components are available from National Semiconductor Corporation unless specifically designated otherwise below. ~efore continuing with a detailed des-cription of operation, a list of components and component values corresponding to components identified in the above description is given below.
With re:Eerence to components illus-trated in Fig. 2:
Transistor 44 2N2222 Transistor 46 2N2222 Voltage Regula-tor 48 7805K
Resistor 32 .38 Ohms (Nichrome Wire) Commutating Resister 36 470 Qhms Resistor 54 470 Ohms Resistor 40 and 42 470 Ohms Capacitor 38 470 ~'icro Farads With reference to components illustrated in Fig. 3:
Logrithmic LED Bar Graph Driver LM 3915 Ouad D flip-flops 26 74LS175 Inverter/Drivers 4049CMoS
(not specifically labelled) Potentiometer 66 5K Ohm multi-turn potentiometer Potentiometer 68 500 Ohm potentiometer Resistor 60 120 Ohms With reference to the components illustrated in Fig. 4:
Flip-flops 70 4027 dual JK master slave fLip-flop with set and reset Counter 80 ~o 4017 Decade counter/
dividers with 10 decade outnuts NAND and NOR gates Standard 4000 series CMOS
(not specifically labelled) logic gates 4023 (3 input NAND gates) 4011 (2 input NAND ~ates) 4001 (2 input NOR gates) ~esistors 78 5~)1C Ohm Capacitor 76 .~ icro Farads Uetailed Descri~tion of Operation Referring to the control circuit 22 shown in Fig. 4, the control circuit includes 4 inputs which are processed so -that the digital logic circuitry se:Lectively provides ~.~ outputs. rrhese outputs include a trigger pulse to SC~ 30, a trigger pulse to ~CR 3~, a sample latcLI pulse, and a reset signal to counte.r ~0. The trigger pulse to SCR 30 results in connecting the predetermined electrical test load 18 to the battery, and the trigger pulse to SCR 3~ results in turning off SCR 30, disconnecting t~st load 18, and connecting the commutating resistor 36 to the battery 12. The sample latch pulse results in th~ digital signal output from the bar graph driver 24 being stored in the flip-flops 26 and displayed by the LED bar graph display 2~. ~he reset pulse causes counter 80 to initiate a ~ew count to produce inputs to the digital circuitry which results in producing the outputs just described.
A normal cycle of testing the state of battery charge is as follows. Assuming the accelerator pedal is down and the battery is connected to an external load 1~, the counter 80 begins to count pulses from the oscillator 72 and after approximately 5 seconds, the output from Q~ of counter 80 enables the control circuit means 22 for a test. If -thereafter, the peclal is released and moved up, a 5 volt signal is applied, and the counter 80 is reset and counts for a short delay time of approximately 3/~ of a second. The counter 30 then proauces an output which causes the control circuit means 22 to pro-duce a trigger pulse transmitted to SC~ 30. This causes the kno~n l~g637~
test load 18 to be placed across the battery terminals causing the predetermined current pulse to flow out of the ba~tery. During the period when the test load 13 is connected to the battery 12, the battery voltage is sensed by the voltage sensor and converter 24 and converted to a plurality of digital outputs which are presented to the digital storage means or flip-flops 26. At the end of -the 3/4 second period, the counter ~0 again resets and counts for a short delay period, approximately 1/2 of a second, and thereafter produces an output which causes the control circuit 22 to produce a sam~le latch pulse whicl~ causes the digital signals produced by the voltage sensor 24 to be transferred into the digital storage device 26, the sample latch pulse being transmitted to the clock inputs of the flip-flops 26 as illustrated. The value of the storage signal re-presents the battery state of charge and is displayed in linear fa!shion by the bar graph display 28. After the sample latch pulse, the next clock pulses cause the control circuit to produce a trigger p~lse transmitted to SCR 34 to disconnect the test load lS and end the test. The trig~er pulse for SCR 34 occurs approximately 1/4 of a second after the sample latch pulse. Ihis completes the test pro-cess if the accelerator pedal has remained undepressed during the entire test period, approximately 1.5 seconds. If the accelerator pedal were depressed during the test period, the sequence of steps described above would be unaltered, except that the sample latch pulse would not be produced-~o that the state of char~e display would remain unchanged from the prior completed test. This prevents storing an erroneous value in the digital storage device 26, which could be caused by unknown loading of the battery 12 if the accelerator were depressed during the test.
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The test process will not be initiated unless the accelerator pedal h~s been down for at least 5 seconds prior to the accelerator pedal being released and the test process being initiated. This minimum down time of 5 seconds prevents erroneous reading of battery voltage which may result from battery recovery or surface charger Similarly, the predetermined time of l/2 o~ a second during which the test load is connected to the battery is provided for the battery voltage to sta~ilize and remove any battery surface charge so that an accurate state of charge reading can be obtained. The initial 3/4 of a second delay prior to connecting the test load is to prevent erroneous reading of transient battery voltage resulting from disconnection from the external loadO
Fig. 5 comprises a control circuit timing diagram which graphically illustrates the description of operation given above. During the period of time noted as t3 , the accelerator foot pedal is depressed for a time less than the minimum downtime of approximately 5 seconds. If this condition occurs, no action is taken by the control circuit 22. The battery must be loaded for at least 5 seconds before the system is able to take a voltage sample, thus minimizing erroneous readings due to battery recovery during long rest periods.
The period of time designated t2 illustrates the situation wherein the accelerator foot pedal is depressed for a time greater than the minimum down time, released, then depressed again before the sampling process is complete~ In this situation the control circuit triggers SCR 30, delays 3/4 of a second and then triggers the SCR 34. No sample latch occurs and thus no voltage sample is entered into the digital storage 26. The time period t3 illustrates ~19-637~
a normal sampling cycle. In this si-tuation, the control circuit triggers SCR 30, waits approximately l/2 of a second, takes a voltage sample, and approximately 1/4 o~ a second later triggers SCR 34 to disconnect the test load.
In summary, during a normal battery voltage test cycle, assuming the accelerator pedal has been depressed for 5 seconds or longer prior to the pedal being released, the test load 18 will be connected to the battery after a short time delay~ on the order o 3/4 of a second. The battery voltage sensed will be converted and stored in the digital storage 26 after a short delay, on the order of 1/2 of a second, causing the state of charge to be displayed on the L~D bar graph display 28. After another short delay on the order of 1/4 of a second, the test load 18 will be disconnected from the battery 12 with SCR 34 being turned on and the commutating resistor 36 remaining connected to the battery until a test cycle is repeated. The commutating resistor 36 is of a relatively high resistance to minimize current drain from the battery.
As noted earlier in the general description, a relatively large current pulse, approximately 25 amps, is drawn by the test load 18. This current is equal to the rated current of a typical lead-acid battery and is utilized in connection with generation of a battery voltage discharge curve such as is illustrated in Fig. 6.
Referring to Fig. 6, the battery discharge curve is generated in response to the battery ~eing selectively connected to a test load to draw 25 amps over a period of 8Q minutes. For a typical 12 volt battery of the type designed to produce a 25 amp current, and assuming a current draw of 25 amperes as illustrated in Fig. ~, the battery voltage discharge curve ranges from a voltage of approximately 11.
~;1963~9 vol~s at full charge to 10.5 volts, which represents f~lll discharge of the battery. As is apparent from tl~e battery voltage clischarge curve, such curve is non-linear and similar to a logarithmic curve in that the battery voltage begins to decrease more rapidly as the battery reaches its full discharge state. The battery voltage decreases because the internal resistance of the battery decreases as the battery becomes discharged. The voltage sensor and converter 24 operates to electrically process the sensed voltage of the bat-ter~. to compensate for the non-linear battery discharge curve to provide a substantially linear visual signal of the state of charge of the battery. In the preferred embodiment as illustrated, outputs 3 through 10 of the logarithmic LED bar graph driver 2~
were utilized to provide the digital signals to be stored and to illuminate the ~ LEDs in tlle bar graph display 28. As illustrated by the top line in Fig. 6, 8 LEDs are illuminated when the battery has a full charge, 7 LEDs are illuminated when the battery voltage drops to 11.7 volts, 6 LEDs are illuminated when the ba~tery voltage drops to 11.63 volts, etc. As is apparent from Fig. 6, the voltage sensor and converter means processes the voltage to compensate for the non-linear battery voltage discharge curve to provide a sub-stantially linear visual signal of the state of charge of the battery.
Other voltage sensor and converter means arrangements could be util-z~d to process the sensed voltage and compensate for the non-linear battery voltage discharge curve.
Calibration of the state of charge indicator l~ as des-cribed above is achieved by connecting a fully charged battery, subject to a 25 amp load, to the voltage sensor and adjusting potenti-ometer 66 until all the LEDs of the bar graph display 28 are just 37 ~
~urned on. The potentiometer 66 reduces the voltage sensed to approximately a 5 volt range. Thereafter, to calibrate for the fully discharged battery state, 10.5 volts is connected to the voltage sensor 24 and potentiometer 68 is adjusted until the last one of the LEDs just turns off. The logarithmic LED bar graph driver 24 ~odel ~3915 internally utilizes voltage comparators and a series of resistors which provide outputs (3-10) which sequentially turn off LEDs 1 through 8 as the battery voltage sensed drops from 11.~ to 10.5 volts. The logarithmic-like characteristic of the bar graph driver 24 provides reasonably good compensation for the non-linear battery voltage discharge curve so that the resultant state of charge indicator provides a linear visual display re presentative of the state of charge remaining before the battery is fully discharged. Put another way, the visual state of charge is linear because the relationship between the battery state of charge and the number of LEDs illuminated is such that a change in one is generally proportional to a change in the other, i.e., when 1/8 of the battery charge has been utilized, 7 of 8 diodes are illumi-nated, when 1/2 of the battery charge has been expended, 4 of 8 diodes are illuminated, when 3/4 of the battery charge has been utilized, 2 of the 8 LEDs are illuminated, etc.
It should be appreciated that the invention can be applied and used with batteries other than lead-acid batteries, by establishing a battery voltage discharge curve for the battery to be tested and then providing a voltage sensor and converter which compensates for the non-linear curve to provide a linear visual display of the battery state of charge. Also, as discussed earlier, a state of charge in-dicator can be made to work with a variety of voltages and/or currents - ~9~ 7~
by changing the values of the test load 18, commutating resis-tor 36, and commutating capacitor 38 included in the electronic switch means 20 For example, the -tester could be utilized by making such modifications with electrical vehicle batteries of the type having a standard test load drawing 75 amps from the batteries.
It is to be understood that the invention is not confined to the particular method and particular construction and arrange-ment of circuit components herein illustrated and described, but embraces all such modifications thereof as come within -the scope of the following claims.
FIELD OF THE IN~ENTION
The inv~ntion relates -to apparatus for indicating -the state of charge of a battery or batteries, such apparatus being useful, by way of example, in electric vehicles having lead-acid batteries.
BACKGROUND PRIOR ART
In an electric vehicle o~ the type cmploying lead-acid batteries, it is desirable for the driver to have a continuous reading of the state of charge of the batteries in the vehicle.
One characteristic of lead-acid batteries is that the discharge curve of the batteries is not linear! that is, the terminal volt-age of the batteries tends to remain fairly constant during initial discharge of the bat~eries when the batteries are discharged at a constant current draw, but the voltage tends to decrease relatively rapidly as the battery approaches its fully discharged state.
Despite this characteristic of the batteries commonly used in an electric vehicle, it is necessary that the state of charge indicator provide an accurate readout of ~he charge remaining in the battery throughout the period of discharge of the battery.
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3~7~
S ~IARY OF THE INVENTION
The invention provides a method of producing a visual signal of the state of charge of a battery having a non-linear battery voltage discharge curve, the method comprising the steps of selectively connecting a predetermined electrical test load to the battery for a predetermined period of time to draw a current pulse from the battery while the battery is disconnected from the external electrical load, sensing the voltage of the battery when the selected electrical test loa~ is connected to the battery terminals, and electrically processing the sensed voltage to compensate for the non-linear battery discharge curve to provide a linear visual signal of the state of charge of the battery.
The invention also provides a method for producing a visual signal of the state of charge of a battery selectively connected and disconnected from an external electrical load, the method comprising the steps of selectively connecting an electrical test load to the battery for a predetermined period of time to draw a predetermined current pulse from the battery while the battery is disconnected from the external electrical load, sensing the volta~e of the battery when the selected electrical test load is contlectecl to the battery terminals, and converting the sensed voltage to a visual si~nal of the state of charge oE the battery.
The invention also provides a method for repeatedly testing the charge of a battery which is operably connected and disconnected from an external load, the method comprisincJ the steps oc selectively connecting a selected resistance to the battery for a selected time interval to produce a predetermined pulse o~ current from the battery, sensincJ the voltage of the battery during the interval, converting the sensed voltage to a digital signal, transmitting the digital signal to a digital signal storage means at a selected time, and converting the digital signal stored in the storage means to a visible display.
The invention also provides a method of testing the state of charge of a battery, which method comprises the steps of connecting the battery to a first load, sensing how long the battery is connected to the first load, disconnecting the battery from the first load and connecting a second load to the battery after the battery has been connected to the first load for a predetermined period of time, and producing, in response to the second load being connected to the battery, a signal indicating the state of charge of the battery.
The invention also provides apparatlls for measuring the state of charge of a battery selectively connected and disconnected from an external load, the apparatus comprising an electrical test load, means for selectively connecting the electrical test load to the battery for a predetermined period of time to draw a predetermined current pulse from the battery while the battery is disconnected from the external load, means for sensing the volta~e across the battery terminals when the selected test load is connected to the battery terminals, and means for converting the voltage sensed to a visual signal of the state of charge of the battery.
The invention also provides a state of charge indicator for repeatedly testing the charge of a battery which is adapted to be alternately operably connected and disconnected from an external load, the state of charge indicator comprising means for selectively ccnnecting a selected resistance to the battery for a selected timed interval to produce a pulse of current from the battery, means for sensing the voltage of the battery during the interval, means for converting the sensed voltage to a digital signal, means for receiving and storing the digital signal, means for converting the digital signal stored in the means for receiving and storing to a visible display, and means for disconnecting the selected resistance from the battery.
3~
The in~ention also provides a state o~
charge indicator for testin~ the state of charge o~ a battery selectively connected to an operating load, which state o:E charge indicator comprises means for sensing if the battery is connected to the operating load timing means ~or sensing how long the battery is connected to the operating load, a test load, means Eor connecting the test load to the battery in response to indication from the load connection sensing means of disconnection of the battery from the operating load after indication from the timing means that the battery was connected to the operating load for a predetermined period of time, and means for producing in response to the test load being connected to the battery a signal indicating the state of charge of the battery.
One of the advantages of the invention is that the method and apparatus of the invention provide a functional means for producing an accurate readout of the charge remaining in the battery, and even though the discharge curve of the battery is non-linear and the voltage of the battery drops off rapidly only as the battery reaches the latter half of its discharge cycle, the state of charge indicator embodying the invention providing an accurate expression of the charge left in the battery.
Various features of the invention are set forth in the following description of a preferred embodiment, in the claims, and in the drawings.
3~9 BPIEF DESCRIPTION OF Tl-IE DRAWINGS
Fig. 1 is a schematic view of a sta-te of charge measuring device embodying the invention.
Fig. 2 is a schematic view of an electronic switch cir-cuit embodied in the state of charge measuring device shown in Fig. 1.
Fig. 3 is a schematic view of a voltage sensor and display assembly embodied in the state of charge measuring device illustrated in Fig. 1.
Fig 4 is a schematic view of a control circuit embodied in the state of charge measuring device shown in Fig. 1.
Fig.. 5 is a schematic illustration of the control circuit timing of the state of charge measuring device illustrated in Fig. 1.
Fig. 6 is a schematic illustration of a typical discharge curve of a battery of the type adapted to be measured using the state of charge measuring device of the invention.
Before describing at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrange-ment of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways.
Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.
3~7~
~ PR~FERRED_EMBODIMENT
Illustrated in Fig. 1 is a state of charge indicator 10 embodying the present invention and adapted to produce a visual signal indicating the state o.E charge of the battery 12 or a bank of batteries which can be, for purposes of example, batteries of the type used in e~ectric vehicles. In the illustrated arrangement the battery 12 is electrically connected to an external load 14. In the case of an electric vehicle the external load 14 would include the electric motor of the vehicle. The means for electrically connecting the battery 12 to the external load 14 includes an accelerator switch 16 adapted to be closed when the accelerator pedal (not shown) of the vehicle is depressed and also adapted to be opened when the accelerator pedal is released.
While the state of charge indicator 10 described will be referred to, for purposes of example, in connection with an electric vehicle, it will be understood that the state of charge indicator 10 will have a variety of other uses and will be useful as a battery charge indicator in a number of other applications.
The state of charge indicator 10 shown in Fig. 1 includes an electrical test load 18 and means for selectively connecting the battery 12 to the test load 18 for a very brief period when the accelerator switch 16 has first been closed for a first predetermined length of time and when the accelerator switch 16 has subsequently been opened for a second predetermined length of time. The test load 18 comprises a resistance which produces a current pulse of relatively large magnitude :Erom the battery 12, the magnitude of the current drawn by the test load 18 being intended to be approximately the same as the average current drawn by the external -; -7 3~79 load 14. The means for selectively connecting the battery 12 to the test load 18 also includes an electronic switch means 20 adapted to selectively connect the test load 18 to the battery 12 and to then disconnect the test load lS from the bat~ery 12 after -the passage of a short time interval. The means for selectively con~
necting also includes a control circuit means 22 for selectively causing the electronic switch means 20 to connect the test load 18 to the battery 12.
Means are further provided for sensing the voltage across the terminals of the battery 12 during the period when the battery 12 is connected to the test load 18. In the arrangement illustrated in Fig. 1, this sensing means includes a voltage sensor and converter 24 to be described in greater detail hereinafter. ~eans are also provided for converting the sensed voltage to a visual signal of the state of charge of the battery. In the illustrated arrangement this means includes a digital storage device 26 and a display device 28. During the period when the electronic switch means 20 connects the battery 12 to the test load 13, the voltage sensor and converter 24 converts the sensed voltage to a plurality of digital signals.
These digital signals are then selectively transmitted from the voltage sensor converter 24 to the digital storage device 26 and the digital storage device 26, in turn, transmits the digital signals to the display device 23.
Referring now mor,e specifically to the control circuit means 22, in the illustrated arrangement the control circuit means is provided with means for selectively causing the electronic switch 20 to connect the battery 12 to the test load 13 when the accelerator switch has first been closed for at least approximately 5 seconds and then has been opened for a second selected time period, such as 3/4 of a second. By first requiring the battery 12 to be loaded for at least 5 seconds before the voltage sensor and converter 24 sense the voltage of the battery, the system prevents any erroneous readings of the terminal voltage o,F the battery which might otherwise occur due to the affects of battery recovery during long rest neriods.
For example, if the battery 12 is allowed to rest for an extended period of time, the voltage of the battery may return to an arti-ficially high level and an ini~:ial sample of the terminal voltage of the battery 12 could show the battery to be fully charged.
However, if the battery is discharged or connected to a load, the battery will quickly lose this high voltage level and return to a voltage level more nearly approximating that measured before the battery is allowed to rest.
The control circuit means 22 also includes means for trans-mitting a signal to the digital storage device 26 and to cause the delay of approxi~ately 0.5 seconds after the voltage has first been sensed by the voltage sensor and converter 24 before the signals from the voltage sensor and converter 24 can be received by the digital storage device 26.
The control circuit 22 further includes means for trans-mitting a signal to the electronic switch means 20 causing the elec-tronic switch means 22 to disconnect the test load 18 from the battery 12 after the signals from the voltage sensor and converter 24 have been transmitted to the digital storage means 26 and also received by the digital display device 28.
Referring now more particularly to the means for converting the sensed voltage to a visual signal, while the display device 2S
could have various constructions, in a preferred from of the invention it can include a plurality of light emitting diodes arranged linearly and which will be described more particularly hereinafter. The light emitting diodes are electrically connected to the digital storage 7~
means 26 such that when the battery 12 is fully char~edthe digital signal~ transmitted to each of the diodes ca~ses them to be illuminated, and then as the state of charge of the batte~y 12 is decreased, the signals to succeeding ones of the light emitting diodes are changed such that a decreasing number of diodes are illuminated. In the illustrated arrangement the display device includes 8 light emitting diodes, out it will be understood that in other arrangements other types of display devices could be used.
Figs. ~-4 illustrate more particularly one arrangement of electrical components and circuits which function to produce the results described above. Before describing in detail the specific apparatus illustrated in Figs. 2-4, it should be understood that the functions of the control circuit 22, the voltage sensor and converter 24, and the digital storage device 28 could be implemented with a microprocessor with a minimum number of support components ~dditionally, if the state of charge indicator is included in a vehicle having an on-board computer, many of these functions could be conveniently embodied in such a computer with a resulting substantial savings in cost of components. Furthermore, while in the following description the various components are described as being used in connection with testing the state of charge of a 12 volt battery adapted to produce a current of 25 amps, it will be understood that the illustrated apparatus could be conveniently modified for use in measuring the state of charge of batteries adapted to produce larger or smaller currents. For example, the state of charge indicator l~ could be conveniently modified so as to be useful in conventional electric vehicles of the type which commonly employ batteries adapted to generate 75 amperes.
Fig. 2. is a schematic view of the electonic components which preferably make up the electronic switch means or switch 20 daigramatically shown in Fig. 1 and also showing the test load 18 as comprising a resister electrically connected to the compenents of the electronic swithc 20.
Various electronic switch means arragements are possible. In the preferred embodiment illustrated in Fig. 2, such switch means comprises a thyristor or SCR 30 which is triggered to selectively connect the test load 18 to the battery 12 to draw a relatively large predetermined current pulse from the battery 12, while the battery is disconnected from theexternal load 14.
The electonic switch 20 includes anothet SCR 34 connected in circuit with a resister 36 and capacitor 38 as illustratred to form a commutating circuit, i.e., triggering SCR
34 turns off SCR 30, and vice versa. Resistoers 40 and 42 are connected to driver transistors 44 and 46, which in tunr are connected to provide trigger pulses to SCRs 30 and 34, respectively, subject to trigger outputs from the control circuit means 22, as will be described further below. A
voltage regulator 48, is connectd to the battery to provide a 5 volt positive supply as shwon.
Two fuses 50 and 52, respectively, are connected as shown. Fuse 50 preferably should be a fast acting fuse that will blow if any current above IT (load current during test), flows in the circuit. Fuse 52 prefeably should be a slower acting breaker (about one second before blowing) that will blow if a current of about IT/2 flfows in the circuit for anb extendied period of time. This protects the compinents in the event that the SCR 30 gets "stuck" on or the control circuit malflunctions.
A Euse out indicator, made up oE a resistor 54 connected to a switched 12 volt supply and to an LED 56, in turn connected to a grounded resistor 58, is also provided.
The design of the commutating circuit will be se~
forth more specifically below. For purposes of discussion, tne commutating resistor 36 has a value equal to Rc ~ the test load resistor 18 has a value equal to R1 and the saturation voltage of SCR 30 has a value equal to VscRsat. E is battery voltage. - .
IT = current through the test load 18 during the test interval.
RL is chosen first.
It is known E ~ VSCRSat. T L
so RL = E ~ VSCRSat.
IT ~1) C (the capacitance of capacitor 38) must be large enough to keep SCR 30 reverse biased through its entire turnoff time, Toff ' Toff ~ RLC
or C = Toff RL (2) Given the conduction time, TC ~ of SCR 30, the resistance RC 20 may be found.
TC = RC
or Rc = TC
C (3) TC should be made large enough so that RC is large and the current drain oE IRC is not substantial. TC is fixed at approximately 0.5 seconds by the control clrcuit 22.
A safety factor of 2 will be incorpora~ed into equations (2) and (3) giving C = 2Toff RL (2a) andRC = TC
2C (3a) In the illustrated embodiment, testing was done on a 12 volt battery of the type rated to produce a current of 25 amperes. Accordingly, the commutating circuit was designed for E=12 volts and I=25 amperes.
The SCRs used were General Electric C122s.
The saturation voltage of the SCRs was found to be approximately 2.5 volts at 25 amps. The turn off time was estimated to be 80 microseconds.
Using these values, RL, and RC and C were calculated.
RL = 0.38 Ohms (made from Nichrome wire) RC = 532 Ohms (470 Ohms was used) C = 421 Micro Farads (a Micro Farad was used in the circuit) The above discussion of design demonstrates one of the advantages of this invention. The state of charge indicator can be made to work with a variety of batteries by simply changing the values of RL, Rc and C.
A further descriptioa of the electronic switch ~0 will be given in the detailed description of operation section aEter description of the schematic circuit arrangements shown in Figs. 3 and 4.
Fig. 3 is a schematic view of the voltage sensor and converter 24, the digital storage means 26, and the display device 28. Various voltage sensor and display means arrangements are possible. In the preferred embodiment illustrated in Fig. 3, the voltage sensor and converter 24 comprises a logarithmic LED bar graph driver, the digitai storage means 26 is comprised of a pair of Quad D flip-flops, and the display device 28 comprises an 8 LED bar graph display, all connected as illustrated. As shown, the digital storage means or flip-flops 26 are connected to an unswitched 5 volt supply provided by voltage regulator 48 (Fig. 2). The 5 volt supply is unswitched so that the state of charge is retained when other switched components are turned off. The digital storage clock inputs tcLK) are connected to the sample latch output of the control circuit 22 as shown and further described below. Noise filter capacitors 60 are connected to the unswitched 5 volt supply and the flip-flops 26 as shown. In addition, inverter/drivers 61 are connected between the outputs of the flip-flops 26 and the LED bar graph display 28 as shown. The anodes of the eight LEDs, numbered 1 through 8, of the bar graph display are connected through resistor 62 to a switched 5 volt supply provided by the voltage regulator 48. A
protective diode 64 is connected between the anodes and ground to limit reverse voltage spikes across the LEDs. The voltage sensor and converter 24 is connected to the positive battery terminal or battery voltage to be sampled via potentiometer 66. In addition, a potentiometer 68 is connected to ~19~3~9 driver 24 to allow for calibration of the s-tate of charge indicator 10 as will be further described in the detailed description of operation section below~
Fig. 4 is a schematic view o~ the control circuit m e ans 22, as diagramatically shown in Fig. 1. I~hile various control circuit means arrangements are possible, in the preferred embodiment illustra-ted in Fig. 4, such means comprises a di~,ital logic circuit including NAND or NOR gates (not separately labelled), our dual JK master slave flip-flops 70 with set and reset, model 4027, an oscillator, generally designated 72, and made u~ of three inverter/d~ivers 74, a capacitor 76 and two resistors 78, and a counter ~O made up of two decade converter/drivers ~2 with 10 decade outputs, model 4017, all connected as shown. An inverter/driver 84 is connected to the Q9 output of counter 80 and an inverter/driver ~6 is connected at the accelerator input as shown.
Ihe digital logic and,o-ther components which have been described Qnd which make up the state of charge indicator 10 can be made up of separately available commercial components, having generic model numbers as designated below. Such components are available from National Semiconductor Corporation unless specifically designated otherwise below. ~efore continuing with a detailed des-cription of operation, a list of components and component values corresponding to components identified in the above description is given below.
With re:Eerence to components illus-trated in Fig. 2:
Transistor 44 2N2222 Transistor 46 2N2222 Voltage Regula-tor 48 7805K
Resistor 32 .38 Ohms (Nichrome Wire) Commutating Resister 36 470 Qhms Resistor 54 470 Ohms Resistor 40 and 42 470 Ohms Capacitor 38 470 ~'icro Farads With reference to components illustrated in Fig. 3:
Logrithmic LED Bar Graph Driver LM 3915 Ouad D flip-flops 26 74LS175 Inverter/Drivers 4049CMoS
(not specifically labelled) Potentiometer 66 5K Ohm multi-turn potentiometer Potentiometer 68 500 Ohm potentiometer Resistor 60 120 Ohms With reference to the components illustrated in Fig. 4:
Flip-flops 70 4027 dual JK master slave fLip-flop with set and reset Counter 80 ~o 4017 Decade counter/
dividers with 10 decade outnuts NAND and NOR gates Standard 4000 series CMOS
(not specifically labelled) logic gates 4023 (3 input NAND gates) 4011 (2 input NAND ~ates) 4001 (2 input NOR gates) ~esistors 78 5~)1C Ohm Capacitor 76 .~ icro Farads Uetailed Descri~tion of Operation Referring to the control circuit 22 shown in Fig. 4, the control circuit includes 4 inputs which are processed so -that the digital logic circuitry se:Lectively provides ~.~ outputs. rrhese outputs include a trigger pulse to SC~ 30, a trigger pulse to ~CR 3~, a sample latcLI pulse, and a reset signal to counte.r ~0. The trigger pulse to SCR 30 results in connecting the predetermined electrical test load 18 to the battery, and the trigger pulse to SCR 3~ results in turning off SCR 30, disconnecting t~st load 18, and connecting the commutating resistor 36 to the battery 12. The sample latch pulse results in th~ digital signal output from the bar graph driver 24 being stored in the flip-flops 26 and displayed by the LED bar graph display 2~. ~he reset pulse causes counter 80 to initiate a ~ew count to produce inputs to the digital circuitry which results in producing the outputs just described.
A normal cycle of testing the state of battery charge is as follows. Assuming the accelerator pedal is down and the battery is connected to an external load 1~, the counter 80 begins to count pulses from the oscillator 72 and after approximately 5 seconds, the output from Q~ of counter 80 enables the control circuit means 22 for a test. If -thereafter, the peclal is released and moved up, a 5 volt signal is applied, and the counter 80 is reset and counts for a short delay time of approximately 3/~ of a second. The counter 30 then proauces an output which causes the control circuit means 22 to pro-duce a trigger pulse transmitted to SC~ 30. This causes the kno~n l~g637~
test load 18 to be placed across the battery terminals causing the predetermined current pulse to flow out of the ba~tery. During the period when the test load 13 is connected to the battery 12, the battery voltage is sensed by the voltage sensor and converter 24 and converted to a plurality of digital outputs which are presented to the digital storage means or flip-flops 26. At the end of -the 3/4 second period, the counter ~0 again resets and counts for a short delay period, approximately 1/2 of a second, and thereafter produces an output which causes the control circuit 22 to produce a sam~le latch pulse whicl~ causes the digital signals produced by the voltage sensor 24 to be transferred into the digital storage device 26, the sample latch pulse being transmitted to the clock inputs of the flip-flops 26 as illustrated. The value of the storage signal re-presents the battery state of charge and is displayed in linear fa!shion by the bar graph display 28. After the sample latch pulse, the next clock pulses cause the control circuit to produce a trigger p~lse transmitted to SCR 34 to disconnect the test load lS and end the test. The trig~er pulse for SCR 34 occurs approximately 1/4 of a second after the sample latch pulse. Ihis completes the test pro-cess if the accelerator pedal has remained undepressed during the entire test period, approximately 1.5 seconds. If the accelerator pedal were depressed during the test period, the sequence of steps described above would be unaltered, except that the sample latch pulse would not be produced-~o that the state of char~e display would remain unchanged from the prior completed test. This prevents storing an erroneous value in the digital storage device 26, which could be caused by unknown loading of the battery 12 if the accelerator were depressed during the test.
~:~9~i3~
The test process will not be initiated unless the accelerator pedal h~s been down for at least 5 seconds prior to the accelerator pedal being released and the test process being initiated. This minimum down time of 5 seconds prevents erroneous reading of battery voltage which may result from battery recovery or surface charger Similarly, the predetermined time of l/2 o~ a second during which the test load is connected to the battery is provided for the battery voltage to sta~ilize and remove any battery surface charge so that an accurate state of charge reading can be obtained. The initial 3/4 of a second delay prior to connecting the test load is to prevent erroneous reading of transient battery voltage resulting from disconnection from the external loadO
Fig. 5 comprises a control circuit timing diagram which graphically illustrates the description of operation given above. During the period of time noted as t3 , the accelerator foot pedal is depressed for a time less than the minimum downtime of approximately 5 seconds. If this condition occurs, no action is taken by the control circuit 22. The battery must be loaded for at least 5 seconds before the system is able to take a voltage sample, thus minimizing erroneous readings due to battery recovery during long rest periods.
The period of time designated t2 illustrates the situation wherein the accelerator foot pedal is depressed for a time greater than the minimum down time, released, then depressed again before the sampling process is complete~ In this situation the control circuit triggers SCR 30, delays 3/4 of a second and then triggers the SCR 34. No sample latch occurs and thus no voltage sample is entered into the digital storage 26. The time period t3 illustrates ~19-637~
a normal sampling cycle. In this si-tuation, the control circuit triggers SCR 30, waits approximately l/2 of a second, takes a voltage sample, and approximately 1/4 o~ a second later triggers SCR 34 to disconnect the test load.
In summary, during a normal battery voltage test cycle, assuming the accelerator pedal has been depressed for 5 seconds or longer prior to the pedal being released, the test load 18 will be connected to the battery after a short time delay~ on the order o 3/4 of a second. The battery voltage sensed will be converted and stored in the digital storage 26 after a short delay, on the order of 1/2 of a second, causing the state of charge to be displayed on the L~D bar graph display 28. After another short delay on the order of 1/4 of a second, the test load 18 will be disconnected from the battery 12 with SCR 34 being turned on and the commutating resistor 36 remaining connected to the battery until a test cycle is repeated. The commutating resistor 36 is of a relatively high resistance to minimize current drain from the battery.
As noted earlier in the general description, a relatively large current pulse, approximately 25 amps, is drawn by the test load 18. This current is equal to the rated current of a typical lead-acid battery and is utilized in connection with generation of a battery voltage discharge curve such as is illustrated in Fig. 6.
Referring to Fig. 6, the battery discharge curve is generated in response to the battery ~eing selectively connected to a test load to draw 25 amps over a period of 8Q minutes. For a typical 12 volt battery of the type designed to produce a 25 amp current, and assuming a current draw of 25 amperes as illustrated in Fig. ~, the battery voltage discharge curve ranges from a voltage of approximately 11.
~;1963~9 vol~s at full charge to 10.5 volts, which represents f~lll discharge of the battery. As is apparent from tl~e battery voltage clischarge curve, such curve is non-linear and similar to a logarithmic curve in that the battery voltage begins to decrease more rapidly as the battery reaches its full discharge state. The battery voltage decreases because the internal resistance of the battery decreases as the battery becomes discharged. The voltage sensor and converter 24 operates to electrically process the sensed voltage of the bat-ter~. to compensate for the non-linear battery discharge curve to provide a substantially linear visual signal of the state of charge of the battery. In the preferred embodiment as illustrated, outputs 3 through 10 of the logarithmic LED bar graph driver 2~
were utilized to provide the digital signals to be stored and to illuminate the ~ LEDs in tlle bar graph display 28. As illustrated by the top line in Fig. 6, 8 LEDs are illuminated when the battery has a full charge, 7 LEDs are illuminated when the battery voltage drops to 11.7 volts, 6 LEDs are illuminated when the ba~tery voltage drops to 11.63 volts, etc. As is apparent from Fig. 6, the voltage sensor and converter means processes the voltage to compensate for the non-linear battery voltage discharge curve to provide a sub-stantially linear visual signal of the state of charge of the battery.
Other voltage sensor and converter means arrangements could be util-z~d to process the sensed voltage and compensate for the non-linear battery voltage discharge curve.
Calibration of the state of charge indicator l~ as des-cribed above is achieved by connecting a fully charged battery, subject to a 25 amp load, to the voltage sensor and adjusting potenti-ometer 66 until all the LEDs of the bar graph display 28 are just 37 ~
~urned on. The potentiometer 66 reduces the voltage sensed to approximately a 5 volt range. Thereafter, to calibrate for the fully discharged battery state, 10.5 volts is connected to the voltage sensor 24 and potentiometer 68 is adjusted until the last one of the LEDs just turns off. The logarithmic LED bar graph driver 24 ~odel ~3915 internally utilizes voltage comparators and a series of resistors which provide outputs (3-10) which sequentially turn off LEDs 1 through 8 as the battery voltage sensed drops from 11.~ to 10.5 volts. The logarithmic-like characteristic of the bar graph driver 24 provides reasonably good compensation for the non-linear battery voltage discharge curve so that the resultant state of charge indicator provides a linear visual display re presentative of the state of charge remaining before the battery is fully discharged. Put another way, the visual state of charge is linear because the relationship between the battery state of charge and the number of LEDs illuminated is such that a change in one is generally proportional to a change in the other, i.e., when 1/8 of the battery charge has been utilized, 7 of 8 diodes are illumi-nated, when 1/2 of the battery charge has been expended, 4 of 8 diodes are illuminated, when 3/4 of the battery charge has been utilized, 2 of the 8 LEDs are illuminated, etc.
It should be appreciated that the invention can be applied and used with batteries other than lead-acid batteries, by establishing a battery voltage discharge curve for the battery to be tested and then providing a voltage sensor and converter which compensates for the non-linear curve to provide a linear visual display of the battery state of charge. Also, as discussed earlier, a state of charge in-dicator can be made to work with a variety of voltages and/or currents - ~9~ 7~
by changing the values of the test load 18, commutating resis-tor 36, and commutating capacitor 38 included in the electronic switch means 20 For example, the -tester could be utilized by making such modifications with electrical vehicle batteries of the type having a standard test load drawing 75 amps from the batteries.
It is to be understood that the invention is not confined to the particular method and particular construction and arrange-ment of circuit components herein illustrated and described, but embraces all such modifications thereof as come within -the scope of the following claims.
Claims (48)
1. A method of producing a visual signal of the state of charge of a battery having a non-linear battery voltage dis-charge curve, the method comprising the steps of:
selectively connecting a predetermined electrical test load to the battery for a predetermined period of time to draw a current pulse from the battery while the battery is disconnected from the external electrical load, sensing the voltage of the battery when the selected electrical test load is connected to the battery terminals, and electrically processing the sensed voltage to compensate for the non-linear battery discharge curve to provide a linear visual signal of the state of charge of the battery.
selectively connecting a predetermined electrical test load to the battery for a predetermined period of time to draw a current pulse from the battery while the battery is disconnected from the external electrical load, sensing the voltage of the battery when the selected electrical test load is connected to the battery terminals, and electrically processing the sensed voltage to compensate for the non-linear battery discharge curve to provide a linear visual signal of the state of charge of the battery.
2. A method for producing a visual signal of the state of charge of a battery selectively connected and discon-nected from an external electrical load, the method comprising the steps of:
selectively connecting an electrical test load to the battery for a predetermined period of time to draw a predetermined current pulse from the battery while the battery is disconnected from the external electrical load, sensing the voltage of the battery when the selected electrical test load is connected to the battery terminals, converting the sensed voltage to a visual signal of the state of charge of the battery.
selectively connecting an electrical test load to the battery for a predetermined period of time to draw a predetermined current pulse from the battery while the battery is disconnected from the external electrical load, sensing the voltage of the battery when the selected electrical test load is connected to the battery terminals, converting the sensed voltage to a visual signal of the state of charge of the battery.
3. A method as set forth in Claim 2 wherein the step of converting the sensed voltage to a visual signal of the state of charge of a battery comprises the steps of. converting the sensed voltage to a signal, transmitting the signal to a storage means, and converting the stored signal to a visual display.
4. A method as set forth in Claim 2 wherein the magnitude or the current pulse drawn from the battery by the electrical test load approximates the magnitude of the current drawn by the external load when the external load is selectively connected to the battery.
5. The method as set forth in Claim 2 and wherein the selected test load is connected to the battery after the battery has been connected to the external load for a first selected period of time and after the battery has subsequently been dis-connected from the external load for a second selected period of time.
6. The method as set forth in Claim 2 and further in-cluding the step of interrupting electrical connection of the battery and the selected test load when the external load is operably connected to the battery.
7. The method as set forth in Claim 2 wherein the step of converting the stored signal to a visual display includes the steps of transmitting the stored signal to a plurality of select-ively illuminated display elements, the number of display elements illuminated being dependent on the stored signal transmitted.
8. A method as set forth in Claim 2 wherein said step of selectively connecting the test load to the battery includes the step of delaying connection of the test load to the battery for a selected time interval after the external load is dis-connected from the battery, and further including the step of delaying transmission of the signal to the storage means for a selected time period.
9. A method as set forth in Claim 8 wherein the test load is selectively connected to the battery after the external load has been connected to the battery for at least approximately 5 seconds, and wherein the test load is connected to the battery for less than 1 second.
10. The method as set forth in Claim 2 and further in-cluding the step of maintaining the visual display until the prior recited steps are repeated.
11. A method for repeatedly testing the charge of a bat-tery which is operably connected and disconnected from an external load, the method comprising the steps of:
selectively connecting a selected resistance to the battery for a selected time interval to produce a predetermined pulse of current from the battery, sensing the voltage of the battery during the interval, converting the sensed voltage to a digital signal, transmitting the digital signal to a digital signal storage means at a selected time, and converting the digital signal stored in the storage means to a visible display.
selectively connecting a selected resistance to the battery for a selected time interval to produce a predetermined pulse of current from the battery, sensing the voltage of the battery during the interval, converting the sensed voltage to a digital signal, transmitting the digital signal to a digital signal storage means at a selected time, and converting the digital signal stored in the storage means to a visible display.
12. A method as set forth in Claim 11 wherein the selected resistance is connected to the battery after the bat-tery has been connected to the external load for a selected period of time and after the battery has subsequently been disconnected from the external load for a selected period of time.
13. A method as set forth in Claim 11 and further in-cluding the step of delaying transmission of the digital signal to the digital signal storage means for a selected period of time.
14. A method as set forth in Claim 11 and wherein said step of converting the digital signal to a visible display in-cludes providing signals to selected one of a plurality of selectively illuminated display elements and so as to cause a decreasing number of said display elements to be illuminated as the voltage sensed decreases.
15. Apparatus for measuring the state of charge of a battery selectively connected and disconnected from an ex-ternal load, the apparatus comprising an electrical test load, means for selectively connecting said electrical test load to the battery for a predetermined period of time to draw a pre-determined current pulse from the battery while the battery is disconnected from the external load, means for sensing the volt-age across the battery terminals when the selected test load is connected to the battery terminals, and means for converting the voltage sensed to a visual signal of the state of charge of the battery.
16. Apparatus for measuring the state of charge of a battery as set forth in Claim 15 wherein said means for converting said voltage sensed includes means for converting the sensed voltage to a signal, means for selectively storing said signal, and means for converting the stored signal to a visual display.
17. Apparatus as set forth in Claim 15 and wherein said means for selectively connecting said electrical test load to the battery draws a predetermined current from the battery having a magnitude approximating the magnitude of the current drawn from the battery when the battery is connected to the external load.
18. Apparatus as set forth in Claim 15 and wherein the means for selectively connecting includes means for connecting said selected test load to the battery after the battery has been connected to the external load for a first period of time and after the battery has subsequently been disconnected from the ex-ternal load for a second period of time.
19. Apparatus as set forth in Claim 15 and wherein said means for converting said sensed voltage to said visual display includes a plurality of selectively illuminated display elements, means for converting said sensed voltage to a plurality of digital outputs transmitted to corresponding ones of said display elements and for causing said ones of said display elements to be illumi-nated.
20. Apparatus as set forth in Claim 15 and wherein said means for selectively connecting said test load to the battery includes means for delaying connection of said test load to the battery for a selected time interval after the external load is disconnected from the battery.
21. Apparatus as set forth in Claim 15 wherein said means for selectively connecting includes means for connecting said test load to the battery after the external load has been connected to the battery for at least approximately 5 seconds and after the battery has been subsequently disconnected from the external load for less than approximately 1 second.
22. A state of charge indicator for repeatedly testing the charge of a battery which is adapted to be alternately operably connected and disconnected from an external load, the state of charge indicator comprising: means for selectively connecting a selected resistance to the battery for a selected timed interval to produce a pulse of current from the battery, means for sensing the voltage of the battery during said interval, means for con-verting the sensed voltage to a digital signal, means for receiving and storing said digital signal, means for converting said digital signal stored in said means for receiving and storing to a visible display, and means for disconnecting said selected resistance from the battery.
23. A state of charge indicator as set forth in Claim 22 and wherein said means for selectively connecting connects the selected resistance to the battery after the battery has been connected to the external load for a selected period of time and after the battery has subsequently been disconnected from the external load for a selected period of time.
24. A state of charge indicator as set forth in Claim 22 and further including means for delaying transmission of said digital signal to said digital signal storage for a selected period of time.
25. A state of charge indicator as set forth in Claim 22 and wherein said means for converting said digital signal to a visible display includes a plurality of selectively illuminated display elements and means for providing electrical signals to said display elements so as to cause a decreasing number of said display elements to be illuminated as the voltage sensed decreases.
26. A state of charge indicator as set forth in Claim 22 wherein said means for selectively connecting includes means for connecting said test load to the battery after the external load has been connected to the battery for at least approximately 5 seconds and after the battery has been subsequently disconnected from the external load for less than approximately 1 second.
27. A state of charge indicator for testing the state of charge of a battery selectively connected to an operating load, said state of charge indicator comprising means for sensing if the battery is connected to the operating load, timing means for sensing how long the battery is connected to the operating load, a test load, means for connecting said test load to the battery in response to indication from said load connection sensing means of disconnection of the battery from the operating load after indication from said timing means that the battery was connected to the operating load for a predetermined period of time, and means for producing in response to said test load being connected to the battery a signal indicating the state of charge of the battery.
28. A state of charge indicator in accordance with Claim 27 wherein said test load approximates the operating load.
29. A state of charge indicator in accordance with Claim 27 wherein said signal producing means comprises means for sensing a voltage of the battery while said test load is connected to the battery for a second predetermined period of time, and means for converting said sensed voltage to the signal indicating the state of charge of the battery.
30. A state of charge indicator in accordance with Claim 29 and further including means for interrupting said voltage converting means if the operating load is connected to the battery before said voltage sensing means has sensed said voltage for said second predetermined period of time.
31. A state of charge indicator in accordance with Claim 29 and further including means for maintaining said state of charge signal until said voltage sensing means next completes sensing said voltage for said second predetermined period of time.
32. A state of charge indicator in accordance with Claim 27 wherein said timing means also senses how long the battery is disconnected from the operating load, and wherein said test load connecting means connects said test load to the battery after said timing means indicates the battery has been disconnected from the operating load for a short second predetermined period of time.
33. A state of charge indicator in accordance with Claim 32 wherein said short second predetermined period of time is about three-fourths of a second.
34. A state of charge indicator in accordance with Claim 27 wherein said test load connecting means connects said test load to the battery within about one second after the battery has been disconnected from the operating load.
35. A state of charge indicator in accordance with Claim 27 wherein said means for sensing connection of the battery to the operating load includes an accelerator switch.
36. A state of charge indicator in accordance with Claim 27 wherein said predetermined period of time is about five seconds.
37. A state of charge indicator in accordance with Claim 27 and further including moans for storing said signal, and means for converting said stored signal to a visual display.
38. A method of testing the state of charge of a battery, said method comprising the steps of connecting the battery to a first load, sensing how long the battery is connected to the first load, disconnecting the battery from the first load and connecting a second load to the battery after the battery has been connected to the first load for a predetermined period of time, and producing, in response to the second load being connected to the battery, a signal indicating the state of charge of the battery.
39. A method in accordance with Claim 38 wherein the signal is produced by the steps of sensing a voltage of the battery while the second load is connected to the battery for a second predetermined period of time, and converting the sensed voltage to the signal indicating the state of charge of the battery.
40. A method in accordance with Claim 39 and further including the step of interrupting the converting of the sensed voltage to a signal if the first load is connected to the battery before the voltage is sensed for the second predetermined period of time.
41. A method in accordance with Claim 39 and further including the step of maintaining the state of charge signal until the voltage is next sensed for the second predetermined period of time.
42. A method in accordance with Claim 39 and further including the steps of transmitting the signal to a storage device, and converting the stored signal to a visual display.
43. A method in accordance with Claim 38 and further including the step of sensing how long the battery is disconnected from the first load, and wherein the second load is connected to the battery after the battery has been disconnected from the first load for a short second predetermined period of time.
44. A method in accordance with Claim 43 wherein said short second predetermined period of time is about three-fourths of a second.
45. A method in accordance with Claim 38 wherein the second load is connected to the battery within about one second after the battery has been disconnected from the first load.
46. A method in accordance with Claim 38 wherein the predetermined period of time is about five seconds.
47. A method in accordance with Claim 38 and further including the steps of selectively storing the signal, and converting the stored signal to a visual display.
48. A method in accordance with Claim 38 wherein the second load is different from the first load.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/362,548 US4520353A (en) | 1982-03-26 | 1982-03-26 | State of charge indicator |
| US362,548 | 1989-06-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1196379A true CA1196379A (en) | 1985-11-05 |
Family
ID=23426538
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000417594A Expired CA1196379A (en) | 1982-03-26 | 1982-12-13 | State of charge indicator |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4520353A (en) |
| CA (1) | CA1196379A (en) |
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Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3529230A (en) * | 1967-09-20 | 1970-09-15 | Eaton Yale & Towne | Battery testing apparatus |
| DE2610536C2 (en) * | 1976-03-12 | 1979-07-26 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Process for determining the maintenance and state of charge of lead batteries as well as circuitry for carrying out the process |
| DE2742675A1 (en) * | 1977-09-22 | 1979-04-05 | Bosch Gmbh Robert | Charge-state indicator for accumulator - has A=D converter driving chain of LEDs arranged along scale indicating degree of charging |
| JPS5628476A (en) * | 1979-08-14 | 1981-03-20 | Shin Kobe Electric Mach Co Ltd | Remained capacity meter for storage battery |
| US4423379A (en) * | 1981-03-31 | 1983-12-27 | Sun Electric Corporation | Battery testing techniques |
| US4423378A (en) * | 1981-12-04 | 1983-12-27 | Bear Automotive Service Equipment Company | Automotive battery test apparatus |
-
1982
- 1982-03-26 US US06/362,548 patent/US4520353A/en not_active Expired - Fee Related
- 1982-12-13 CA CA000417594A patent/CA1196379A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4520353A (en) | 1985-05-28 |
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