WO1992011680A1

WO1992011680A1 - Battery characteristic detection scheme and apparatus

Info

Publication number: WO1992011680A1
Application number: PCT/US1991/008686
Authority: WO
Inventors: Arthur G.. Burns; Henry A. Bogut
Original assignee: Motorola, Inc.
Priority date: 1990-12-17
Filing date: 1991-11-20
Publication date: 1992-07-09

Abstract

At least one cell (14) having a positive (14A) and a negative (14B) terminal has an electrical element (18) coupled to one of the terminals for providing a component value indicative of a battery capacity and of an associated battery chemistry to a charging means (30).

Description

BATTERY CHARACTERISTIC DETECTION SCHEME

AND APPARATUS

Technical Field

This invention relates generally to batteries and chargers, and more specifically to a scheme for detecting the characteristics of a battery to provide an optimum charging strategy.

Background

Battery packs for portable products are typically available in a variety of capacities and in a variety of battery cell chemistries. A battery charger generally cannot determine the charge capacity and battery cell chemistry inexpensively. U.S. Patent No. 4,006,396 by Bogut discusses an inexpensive universal battery charging scheme which provides an electrical element having a characteristic related to a predetermined charging rate of the battery. This charging scheme as well as other common battery charging schemes fail to distinguish between battery chemistries inexpensively. The optimum charging rate and algorithm for a particular battery cell chemistry may vary drastically. For instance, Nickel Cadmium cells (Ni- Cad) and Nickel Metal Hydride (NI-MH) cells can both use a Temperature Cut-off scheme (TCO), rate of temperature change scheme (Δ T), negative delta Voltage scheme (- ΔV), a second derivative of Voltage scheme (d²V), or a zero rate of change in voltage scheme (Vpeak) to charge their particular batteries. But in the case of temperature schemes, the NI-MH cells may require a shift or compensation in the charging algorithm that may differ for Ni-Cad batteries. Likewise, in the voltage dependent charging schemes, the rate of change of voltage or peak voltage may differ between NI-MH and Ni-Cad. Other battery cell chemistries such as lithium, lead acid, and lithium ion use a constant voltage scheme (Vconstant) that has a different algorithm than NI-MH or Ni-Cad. Each battery chemistry has it's own optimum charging "signature" that allows for a safe rapid charge or trickle charge. Thus, a need exists for a battery charging scheme that not only distinguishes between charge capacities of many different battery capacities available, but further distinguishes between the variety of battery cell chemistries available now and in the future for use in rechargeable batteries and battery packs.

Summary of the Invention

Accordingly, a series of interconnected cells having a positive and a negative terminal has an electrical element coupled to one of the terminals for providing a element value indicative of a battery capacity and of an associated battery chemistry to a charging means.

In another aspect of the present invention, a charging means or charger having a battery capacity and battery chemistry sensing means provides the battery with an optimal charging algorithm in accordance with the element value provide by the battery.

Brief Description of the Drawings Figure 1 is a block diagram of a battery characteristic detector in accordance with the present invention.

Figure 2 is a flow chart of the battery characteristic detection scheme in accordance with the present invention.

Detailed Description of the Preferred Embodiment

Referring to Figure 1 , there is shown a battery characteristic detection apparatus 10 having a charger 30 and battery 12. The battery 12 comprises a series of cells 14 coupled either in serial or in parallel and having a positive electrode 14A and a negative electrode 14B, the negative electrode 14B being coupled to ground point 20 and negative battery contact 27. The positive electrode 14A is coupled to both a charger contact 22 and a positive battery contact 23. Contacts 23 and 27 provide a portable product (not shown) with the coupling points for powering the portable product. The battery further includes a thermistor 16 coupled to ground (20) on one end and coupled to charger contact 24 on the other. Finally, battery 12 preferably comprises a resistor 18 coupled between charger contact 26 and negative anode 14B.

The charger 30 comprises a transformer 32, typically for stepping down the 120VAC (28) from a conventional outlet. The stepped down voltage is rectified and filtered (34) as is known in the art. The current (50) supplied to the battery 12 is regulated by current control circuit 36 which is in turn controlled by a charge current control signal 58 provided by a microprocessor 38. A diode 42 is further provided having a polarity selected to prevent the cells (14) from discharging into the charger 30 which is coupled to the charger contacts 22, 24, and 26.

Operationally, the charger 30 receives several feedback inputs from the battery (12) to be connected and the charger (30) itself that allows the microprocessor 38 to determine the charge algorithm to be provided to the battery 12. Preferably, these inputs would include a battery voltage sense signal 52, a maximum temperature charge control signal 54, a programming battery chemistry and charge capacity control input 56, and an ambient temperature input signal (46 and 48). These inputs may or may not be required, depending on the battery chemistries involved and the charging algorithms to be used. Other inputs may be used to provide further selectivity in charging schemes. The battery voltage sense signal 52 from the current control circuit 36 determines the polarity of the battery 12 or any other battery inserted into the charger 30, so as to provide the appropriate charge current direction. The signal 52 may also provide the battery peak voltage information that may be required in order to provide the appropriate charge to a Nickel Metai Hydride or Ni-Cad battery which have different peak voltages for optimal charging. The signal 52 may likewise provide the constant voltage information that may be required in order to provide the appropriate charge to a lithium, lead acid or lithium ion battery. The maximum temperature charge control signal 54 provided by the thermistor 16 allows the charger to determine when it is appropriate to discontinue charging if a purely temperature cut-off scheme is used. For instance Nickel Metal Hydride or Ni-Cad batteries, as they are charged, reach a temperature which indicates a "complete" charge. If the temperature rises above the "complete" charge temperature, the battery may overcharge and result in significant battery damage. Thus, the charger would be programmed to discontinue charging or go into trickle charge once the "complete" charge temperature is attained. Finally, a second thermistor 44 provides an ambient temperature input signal (46 and 48). The thermistor 44 allows the charger to monitor the ambient temperature surrounding the battery so as to compensate the charging algorithms for batteries that are sensitive to differing ambient temperatures such as Nickel Metal Hydride batteries. Of course, an electronic element 18 indicative of the battery chemistry and battery capacity such as code resistor 18 is used to provide the programming of battery chemistry and charge capacity control input 56. Of course any electronic element providing distinguishable and measurable values such as a resistor, inductor, capacitor, diode, memory device (RAM, ROM, EEPROM, etc.), or a pulse train modulator could be used for this function. In other words, the electronic component 18 (or in this embodiment the code resistor) will indicate to the charger what kind of battery chemistry and battery capacity the inserted battery has. From this indication, a charging algorithm is chosen by the microprocessor from a look-up table or an appropriate memory source (RAM, ROM, EEPROM, etc.) known in the art. Then, the microprocessor, using one or more of the available inputs (i.e., 52, 54, and 46 & 48) adjusts the charge algorithm according to the inputs received. Optionally, the microprocessor 38 can provide a status signal or signals 60 to an output source or status indicator or indicators (40) that would allow a user to know such information as when the charge is complete, what type of battery is being charged, the ambient temperature, or any other parameter desired.

Figure 2, illustrates a typical algorithm in accordance with the present invention. When a battery is first inserted (102) into a charger, the code resistor (or any electronic element having a measurable characteristic value such as an inductor or capacitor) value is read. Preferably, the broader range of the value of the code resistor determines the type of battery chemistry involved. For instance, if the code resistor value is within the "A"-'B" (106) range (10-1000 Ohms for example) then a lithium charge control algorithm (114) is performed. If the code resistor value is within the "C"-'D" (108) range (1001-10,000 Ohms for example) then a Ni-Cad charge control algorithm (128) is performed. If the code resistor value is within the "E"-'F" (110) range (10,001-100,000 Ohms for example) then a Nickel Metal Hydride charge control algorithm (128) is performed. If the code resistor value is not within the desired ranges (i.e., 10-100,000 Ohms), then a defect battery alert (112) is preferably given.

Under each algorithm (114, 128, or 142), the resistance value further provides the battery capacity information (116, 130, 142). For instance within the Lithium algorithm (114), the resistance values of 10-100 Ohms may indicate a 1 hour rapid charge capacity, the resistance value of 101-500 may indicate a 2 hour rapid charge capacity, while a resistance value of 501-1000 may indicate a 3 hour rapid charge capacity. Alternatively, the different resistance values could indicate to the charger to adjust the charging current to provide for a 1 hour charge time for all battery capacity ratings.

The value of the code resistors can be matched up with a look-up table stored in memory. After the resistance value is matched in the look up tables (116, 130, or 144), then the initial charge conditions including current, voltage, temperature, and time are set up (118, 132, or 146). These conditions allow the microprocessor to alter the charging algorithm periodically (or continuously if desired) in accordance with the optimal charging profiles known for a given battery chemistry and capacity. Once the initial charge conditions are set (118, 132, or 146), the battery charging commences (120, 134, or 148). Finally, the microprocessor poles the appropriate input or inputs to determine if the charge is complete (122, 136, 150). For instance, if a Ni- Cad battery is being charged, the microprocessor may receive a signal that the cut-off temperature has been reached by measuring the resistance of the the thermistor 16 of Figure 1. Or the battery voltage sense signal 52 could sense a constant voltage indicative of a complete charge in the case of a rechargeable lithium battery. Or the microprocessor could sense a temperature cut-off level from the thermistor 16 at an ambient temperature (sensed by thermistor 44) that would indicate further charging is required for optimal charging in the case of a Nickel Metal Hydride battery. The tailoring and adjustments of algorithms is simply a function of the status inputs received and the software or look-up comparators used to manipulate the algorithm in response to the status inputs. If the charge is not complete (124, 138, or 152), the charger continues charging. Once the charger determines that a charge is complete, the charger stops charging and a display can indicate "complete" (126, 140, or 154). The use of other battery chemistries not herein mentioned are within the contemplation of the present invention.

What is claimed is:

Claims

1. A battery, comprising: at least one cell, said cell having a positive and a negative terminal; and an electrical element coupled to one of said positive or said negative terminals for providing a electrical element value indicative of a battery capacity and of an associated battery chemistry to a charging means.

2. The battery of claim 1 , wherein said at least one cell is selected from a group consisting of Nickel Cadmium, Nickel Metal Hydride, Lead Acid, Lithium, Zinc-air, and Lithium Ion.

3. The battery of claim 1 , wherein said electrical element is selected from a group consisting of resistors, inductors, capacitors, and diodes.

4. The battery of claim 1 , wherein said battery further comprises battery temperature sensing means and battery voltage sensing means providing a battery temperature signal and a battery voltage signal respectively.

5. A battery charging system having a charging path for charging batteries having a variety of different capacities and chemistries requiring different optimum charging rates and optimum charging algorithms, said system including in combination: a battery capacity and battery chemistry sensing circuit; at least one battery cell having an optimum charging rate and optimum charging algorithm for its capacity and chemistry; and a passive element coupled to at least one said battery cell for providing an impedance indicating said optimum charging rate and said optimum charging algorithm.

6. The battery of claim 5, wherein said chemistries are selected from a group consisting of Nickel Cadmium, Nickel Metal Hydride, Lead Acid, Lithium, Zinc-air, and Lithium Ion.

7. The battery of claim 5, wherein said passive element is selected from a group consisting of resistors, inductors, capacitors, and diodes.

8. A battery charger having a charging path for charging batteries having a variety of different capacities and chemistries requiring different optimum charging rates and an optimum charging algorithm, said charger comprising: a charging rate and battery chemistry sensing circuit for detecting an impedance indicative of a particular battery capacity and a particular charging algorithm for a battery having said particular battery capacity and algorithm ; battery terminals coupled to said sensing circuit for coupling a battery to said sensing circuit.

9. The battery of claim 8, wherein said chemistries are selected from a group consisting of Nickel Cadmium, Nickel Metal Hydride, Lead Acid, Lithium, Zinc-air, and Lithium Ion.

10. The battery of claim 8, wherein said impedance is provided from a group of electrical elements consisting of resistors, inductors, capacitors, and diodes.