Battery charger detecting full charge of batteries using a thermostat and thermistor in a battery pack

• US 5,909,101 A
• Filed: 03/27/1997
• Issued: 06/01/1999
• Est. Priority Date: 03/27/1996
• Status: Expired due to Term

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Watanabe, Hideki, Matsumoto, Toshio, Kasuya, Toshiyasu, Mori, Tatsuki
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US08/835,021
• Time in Patent Office: 796 Days
• Field of Search: 320/110, 320/112, 320/119, 320/123, 320/125, 320/150, 320/154, 320/FOR 134, 320/FOR 105
• US Class Current: 320/110
• CPC Class Codes: H02J 7/007192 in response to temperature
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage

Abstract

A battery charging system is disclosed for charging two different types of battery packs, a known three terminal type including batteries and a thermostat switch, and a newer four terminal type further including a thermistor for sensing battery temperature. A charging control circuit stops charging current to the battery pack when a contact of the thermostat switch is open or when the thermistor detects a temperature above a predetermined temperature. If either the thermostat switch or the thermistor fail to properly operate, charging current to the battery pack is stopped securely to avoid damaging batteries.

Claims

1. A battery charging system, comprising:

a first battery pack including;

a battery to be charged;

a thermistor for sensing a temperature of the battery,

a thermostat having a switch contact that can be open or closed, the switch contact being open when the temperature of the battery is above a predetermined temperature;

a first terminal connected to a first electrode of the battery,

a second terminal connected to a second electrode of the battery,

a third terminal connected to the second electrode of the battery through the thermostat, and

a fourth terminal connected to the second electrode of the battery through the thermistor;

a second battery pack, including;

a battery to be charged;

a thermostat having a switch contact that can be open or closed, the switch contact being open when the temperature of the battery is above a predetermined temperature;

a first terminal connected to a first electrode of the battery,

a second terminal connected to a second electrode of the battery, and

a third terminal connected to the second electrode of the battery through the thermostat; and

a charging unit, including;

charging control means for flowing a battery charging current between the first terminal and the third terminal of the the first battery pack or the second battery pack,

the charging control means being arranged such that

when charging control means charges the first battery pack, the control means stops the flow of charging current when the switch contact of the thermostat is open, or based on a change of resistance value of the thermistor responsive to the battery temperature being above a second predetermined temperature, and

when the charging control means chargers the second battery pack, the control means stops the flow of charging current when the switch contact of the thermostat is open.

2. A battery charger comprising:

a battery pack comprising;

a battery;

a temperature sensor for sensing a temperature of said battery;

a temperature switch capable of being open or closed and adapted to be open when a temperature of said battery is above a first predetermined temperature; and

a charging unit comprising;

means for indicating a problem condition when said temperature switch is closed and said temperature sensor determines that the temperature of said battery is above a second predetermined temperature; and

charging control means for initializing a charging current to flow to said battery pack when said temperature switch is closed and said temperature sensor indicates that said battery pack is at a safe temperature for charging.

3. A battery charger for charging battery packs of first and second types,

the first type of battery pack including:

a battery to be charged;

a thermistor for sensing a temperature of the battery,

a thermostat having a switch contact that can be open or closed, the switch contact being open when the temperature of the battery is above a predetermined temperature;

a first terminal connected to a first electrode of the battery,

a second terminal connected to a second electrode of the battery,

a third terminal connected to the second electrode of the battery through the thermostat, and

a fourth terminal connected to the second electrode of the battery through the themistor;

the second type of battery pack including;

a battery to be charged;

a thermostat having a switch contact that can be open or closed, the switch contact being open when the temperature of the battery is above a predetermined temperature;

a first terminal connected to a first electrode of the battery,

a second terminal connected to a second electrode of the battery, and

a third terminal connected to the second electrode of the battery through the thermostat;

the batter charger, comprising;

charging control means for flowing a battery charging current between the first terminal and the third terminal of the first or second type of battery pack,

the charging control means being arranged such that

when the charging control means charges a battery pack of the first type, the control means stops the flow of charging current when the switch contact of the thermostat is open, or based on a change of resistance value of the thermistor responsive to the battery temperature being above a predetermined temperature, and

when the charging control means charges a battery pack of the second type, the control mans stops the flow of charging current when the switch contact of the thermostat is open.