Rapid battery charger with charge controlling capability depending on overvoltage of the battery

• US 5,905,364 A
• Filed: 02/19/1997
• Issued: 05/18/1999
• Est. Priority Date: 02/20/1996
• Status: Expired due to Fees

• Current Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Original Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Inventors: Ookita, Hirotaka
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/803,022
• Time in Patent Office: 818 Days
• Field of Search: 320/5, 320/14, 320/21, 320/22, 320/29, 320/30, 320/31, 320/32, 320/39, 320/141, 320/145, 320/155, 320/156, 320/FOR 104, 320/FOR 113, 320/FOR 120, 320/FOR 121 , 320/FOR 128, 320/FOR 129, 320/FOR 130, 320/FOR 131, 320/FOR 138
• US Class Current: 320/141
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process

Abstract

A rapid battery charger uses current pulses to quickly charge secondary batteries of various types having a wide variety of charging characteristics. When the current pulse is paused, the voltage across the secondary battery is measured at two different times; the difference in the two voltages is compared with a reference value; and the current is adjusted according to the result of the comparison, thus preventing the generation of gas within the secondary battery.

Claims

1. A rapid battery charger comprising:

a current source for generating a current having a level;

a current switching circuit connected to said current source for turning the current on and off to produce current pulses occurring at a predetermined frequency, the current pulses being supplied to a battery to be recharged, each of the current pulses being on for a first duration of time and off for a second duration of time;

timing setting means for setting a first timing and a second timing in the second duration of time of each of the current pulses, the first timing being set immediately after each of the current pulses is rendered off and the second timing being set after the first timing;

voltage detecting means for detecting a first voltage across the battery at the first timing and a second voltage across the battery at the second timing;

voltage differential computing means for computing a difference between the first voltage and the second voltage and outputting a voltage differential representative of the difference therebetween;

comparison means for comparing the voltage differential output from said voltage differential computing means with a reference value and outputting a comparison output; and

current level controlling means for changing the level of the current in response to the comparison output.

2. The rapid battery charger according to claim 1, wherein when the comparison output represents that the voltage differential has exceeded the reference value, said current level controlling means lowers the level of the current.

3. The rapid battery charger according to claim 1, further comprising reference value changing means for changing the reference value in response to the comparison output.

4. The rapid battery charger according to claim 3, wherein when the comparison output represents that the voltage differential has exceeded the reference value, said reference level changing means changes the reference value to be compared with the voltage differential by said comparison means.

5. The rapid battery charger according to claim 4, wherein when the comparison output represents that the voltage differential has exceeded the reference value, said current level controlling means lowers the level of the current and said reference value changing means changes the reference value to be compared with the voltage differential by said comparison means.

6. The rapid battery charger according to claim 5, further comprising an initial current level setting means for setting an initial level of the current to be generated from said current source.

7. The rapid battery charger according to claim 6, further comprising an initial reference value setting means for setting an initial reference value to be initially compared with the voltage differential.

8. The rapid battery charger according to claim 7, wherein said current level controlling means changes the level of the current in three stages including a first current level, a second current level lower than the first current level and a third current level lower than the second current level, and said initial current level setting means sets the first current level, wherein said reference value changing means changes the reference value in three stages including a first reference value, a second reference value, and a third reference value, and said initial reference value setting means sets the first reference value, and wherein said current level changing means changes the first current level to the second level and concurrently said reference value changing means changes the first reference value to the second reference value when the comparison output represents that the voltage differential has exceeded the first reference value, and said current level changing means changes the second current level to the third level and concurrently said reference value changing means changes the second reference value to the third reference value when the comparison output represents that the voltage differential has exceeded the second reference value.

9. The rapid battery charger according to claim 8, further comprising termination means for terminating charging the battery when the comparison output represents that the voltage differential has exceeded the third reference value.

10. The rapid battery charger according to claim 9, further comprising alerting means for alerting that charging the battery has terminated when said terminating means has terminated charging the battery.

11. The rapid battery charger according to claim 10, wherein said alerting means comprises a buzzer.

12. The rapid battery charger according to claim 10, wherein said alerting means comprises a display.

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

(a) setting currant pulses to be applied to the battery, each of the current pulses having a level, an on duration from a rising edge to a falling edges, and an off duration from the falling edge to a subsequent rising edge of a subsequent current pulse;

(b) setting a reference value;

(c) applying the current pulses to the battery;

(d) detecting a first voltage across the battery at a first timing set immediately after the falling edge of each of the current pulses;

(e) detecting a second voltage across the battery at a second timing set after the first timing in the off duration of each of the current pulses;

(f) computing a difference between the first voltage and the second voltage and outputting a voltage differential representative of the difference therebetween;

(g) comparing the voltage differential with the reference value set in step (b) and outputting a comparison output;

(h) when the comparison output represents that the voltage differential has exceeded the reference value set in step (b), lowering the level of the current pulses and applying the lower level current pulses to the battery;

(i) changing the reference value set in step (b) to a predetermined different value; and

(j) repeating steps (d) through (i) for a predetermined number of times and terminating charging the battery.

14. The method according to claim 13, wherein in step (j), steps (d) through (i) are repeated two times.