Battery charger with three different charging rates

• US 4,670,703 A
• Filed: 05/06/1985
• Issued: 06/02/1987
• Est. Priority Date: 05/06/1985
• Status: Expired due to Term

• Current Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Original Assignee: General Electric Company
• Inventors: Williams, James W.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/730,933
• Time in Patent Office: 757 Days
• Field of Search: 320/22, 320/24, 320/15, 320/21, 320/39, 320/48, 320/30, 320/31
• US Class Current: 320/125
• CPC Class Codes: H02J 7/0018 using separate charge circuits
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: Y10S 320/12 Precharging analysis, e.g. determining presence of battery
• CPC Class Codes: Y10S 320/18 Indicator or display
• CPC Class Codes: Y10S 320/19 Charger status, e.g. voltmeter

Abstract

A circuit for safely and rapidly charging batteries, with the charging occurring at three different rates. A first rate is used to bring a battery up to a level where it is determined to be safe for rapid rate charging. At this charge level the temperature of the battery may also be checked to be sure it is within a safe range for rapid charging. If safe, the battery is then rapidly charged at a second rate, until it is almost at its maximum capacity. At that point a third rate charge, lower than the first charge rate, is used to maintain the battery at nominally full charge. A microprocessor controller controls a plurality of rapid rate chargers and determines when the battery parameters are safe so that rapid charging can be safely employed. The rapid charger may be of a conventional charge pump type.

Claims

1. A three level battery charging circuit comprising:

a dual rate charging circuit connectable across the terminals of a battery to be charged and including an automatic switch means for automatically switching from a first charge rate to a second lower charge rate in response to a sensed battery voltage in excess of a first predetermined threshold voltage;

a further charging circuit providing charging current at a third rate higher than said first rate and connected in parallel with said dual rate charging circuit; and

control means connected to control said further charging circuit so as to switch it to active condition in response to a sensed battery voltage in excess of a second predetermined threshold voltage which is less than said first threshold;

whereby, for a fully discharged battery, the following sequence of charging rates is provided;

(a) said first rate, (b) the combination of said first rate and said third rate, (c) the combination of said second rate and said third rate, and (d) said second rate.

2. A three level battery charging circuit as in claim 1 wherein said dual rate charging circuit comprises:

a voltage reference connected to a voltage comparator and switch circuit including first and second resistances connected in series with the battery to be charged and shorting switch connected in parallel with at least one of said resistances.

3. A three level charging circuit as in claim 2 wherein said control means includes means for automatically turning said further charging circuit on and off in response to sensed battery voltage and temperature conditions so that said third charge rate is applied to the battery only under predetermined conditions of temperature and sensed battery voltage.

4. A three level battery charging circuit comprising:

first means for applying continuous battery charging at a first rate for bringing a battery from a fully discharged state to a predetermined level for receiving a higher charge rate;

second means for applying battery charge at a second rate higher than said first rate for rapid battery recharge; and

third means for applying continuous battery charge at a third rate lower than said first rate to sustain full charge on the battery once a predetermined battery voltage is reached

said first, second and third means being interconnected and inter-related to produce the following sequence of charging rates for a fully discharged battery;

(a) said first rate, (b) said second rate, and (c) said third rate.

5. A circuit for charging a battery at differing combinations of three charging rates:

(a) a first charging rate for bringing battery from discharged state to a predetermined level for high rate charge;

(b) a second rate charge higher than said first rate for rapid battery recharge, and (c) a third charging rate lower than said first rate to sustain full charge on the battery once charging to a predetermined battery voltage is reached, said circuit comprising;

rate control means for (1) determining when said battery is within predetermined limits for said second rate changing, and (2) applying said second rate charge to said battery while said battery is within said predetermined limits;

voltage comparator means for comparing said battery voltage with a reference voltage;

source means for applying a continuous charging voltage and current to a battery;

first and second resistance means for series limiting the continuous charging current applied by said source means;

said first and second resistance means being connected in series with each other and in series with the battery and said source means to provide said first charging rate when at least one of asid resistance means is bypassed and otherwise to provide said third charging rate; and

switching means for bypassing at least one of said first and second resistance means when said voltage comparator means detects said battery voltage increase beyond said reference voltage

whereby, for a fully discharged battery, the following sequence of charging rates is provided;

(a) said first rate, (b) the combination of said first and second rates, (c) the combination of said second and third rates, and (d) said third rate.

6. A circuit as in claim 5 wherein said voltage comparator means comprises a transistor with a zener diode connected between said transistor emitter and ground, said transistor turning on when the voltage on the base of said transistor is greater than the base emitter voltage of said transistor plus the voltage across said zener diode.

7. A circuit as in claim 6 wherein said switching means comprises a transistor.

8. A battery charger system for charging each of a plurality of batteries at different combinations of three charging rates comprising:

measuring means for measuring the voltage of each of said batteries and the temperature of each of said batteries;

control means for determining whether the voltage of each of said batteries and the temperature of each of said batteries is within a predetermined region for applying a predetermined rate charge thereto;

first charging means fo applying said predetermined current charge rate to each of asid batteries, said first charging means being externally controllable in response to said control means, for turning on and off said first charging means;

second charging means for applying a further rate of charge to each of said batteries which is less than said predetermined current charge rate;

first resistance means for initially limiting the charge from said further charging means to a first rate;

second resistance means for subsequently limiting the charge from said further charging means to a second rate which is lower than said first rate;

comparator means for detecting the voltage on each of said batteries and comparing it with a known reference voltage; and

switching means for switching between said first and said second resistance means in response to the signal from said voltage comparator means

whereby, for a fully discharged battery, the following sequence of charging rates is provided;

(a) said first rate, (b) the combination of said first rate and said predetermined rate (c) the combination of said second rate and said predetermined rate, and (d) said second rate.

9. A high rate charging system for a battery comprising:

means for monitoring the temperature of said battery;

means for monitoring the voltage of said battery;

first charging means for supplying a predetermined rate charge to said battery;

control means for;

(1) determining if said battery is in a predetermined condition for charging at said predetermined rate based on the temperature and voltage readings obtained from said means for monitoring temperature and voltage;

(2) initiating and terminating the operation of said first charging means based on said temperature and voltage readings according to a predetermined control sequence; and

(3) suspending said predetermined charging operation temporarily and monitoring said voltage reading only during said suspension; and

bi-level rate further charging means for charging said battery even when said first charging means is not operating;

(a) initially at a first rate and (b) subsequently at a second rate which is lower than said first rate so as to maintain full battery charge

the following sequence of charging rates being provided for a fully discharged battery;

(a) said first rate, (b) the combination of said first rate and said predetermined rate, (c) the combination of said second rate and said predetermined rate, and (d) said second rate.

10. A system as in claim 9 wherein said control means further comprises (4) means for operating an indicator based on the temperature of said battery, said indicator being in one state when said battery is overheating, and a second state when said battery is too cold.

11. A system as in claim 10 wherein said one state is a steady state, and said second state is a "flashing" state.

12. A method for rapidly charging a rechargeable battery, comprising the steps of:

firstly charging said battery at a first rate which is sufficient to raise a fully discharged battery to a first predetermined level;

testing said battery during said first charging step to ensure that predetermined parameters are within predetermined limits;

secondly charging said battery at a second rate which is substantially higher than said first rate;

recurrently testing the voltage on said battery during said second charging step and, terminating said second charge step when said battery has reached substantially full charge; and

thirdly charging said battery thereafter at a third rate substantially lower than said first rate to maintain said battery at its maximum charge while minimizing adverse heating effects on said battery.

13. A method as in claim 12 wherein said recurrently testing step comprises the steps of:

(1) sensing the temperature of said battery and suppressing said second charging step if the temperature of said battery is a predetermined amount in excess of ambient temperature;

(2) applying said second rapid rate charge at a predetermined duty cycle if the temperature of said battery is a predetermined amount less than ambient temperature; and

(3) beginning said second rapid rate charge if said battery is within safe temperature limits.

14. A method as in claim 13 wherein said recurrently testing step further comprises the steps of:

terminating said charging for a short predetermined time within a longer predetermined time period; and

testing the terminal voltage at said battery during this short predetermined time.