Indirect thermal sensing system for a battery charger

• US 5,874,825 A
• Filed: 04/16/1997
• Issued: 02/23/1999
• Est. Priority Date: 05/03/1996
• Status: Expired due to Fees

• Current Assignee: Black & Decker Corporation (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Brotto, Daniele C.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): SHIN, KYUNG E
• Application Number:
  US08/834,375
• Time in Patent Office: 678 Days
• Field of Search: 320/150, 320/151, 320/152, 324/441, 429/62
• US Class Current: 320/150
• CPC Class Codes: H02J 7/007194 of the battery

Abstract

A battery charger including a battery temperature monitoring device. The battery temperature monitoring device includes a first thermistor bonded to one of the terminals of the battery charger to provide a temperature signal of the temperature of the terminal, and a second thermistor positioned within the battery charger to provide a temperature signal of the ambient temperature. The temperature signals from both the first and second thermistors are applied to a temperature monitoring circuit that compares the temperature signals to a known discharge rate of an RC circuit. A microprocessor receives output signals from the temperature monitoring circuit and, using an algorithm, determines the actual temperature of the battery.

Claims

1. A temperature monitoring device for determining the temperature of a battery pack being charged in a charging device, said charging device including a charging terminal, said monitoring device comprising:

an ambient temperature sensor positioned to sense ambient temperature within the battery charger and providing a temperature signal indicative of the sensed ambient temperature;

a terminal temperature sensor positioned to sense the temperature of the charging terminal and providing a temperature signal indicative of the temperature of the terminal;

a temperature monitoring circuit responsive to the temperature signals from the ambient temperature sensor and the terminal temperature sensor, said temperature monitoring circuit providing output signals indicative of the temperature signals, said temperature monitoring circuit including a first comparator, a second comparator and a capacitor, said first comparator being responsive to the temperature signal from the ambient temperature sensor, said second comparator being responsive to the temperature signal from the terminal temperature sensor, and both the first and second comparators being responsive to a voltage potential signal from the capacitor; and

a controller for providing an indication of the temperature of the battery pack based on the temperature signals, said controller being responsive to the output signals from the monitoring circuit, said controller providing a voltage potential signal to the capacitor to charge the capacitor.

2. The temperature monitoring device according to claim 1 wherein the capacitor is part of an RC circuit, said capacitor being charged through a resistor in the RC circuit, wherein the controller removes the voltage potential signal from the capacitor so as to allow the capacitor to discharge, said controller providing counts at an internal clock frequency as the capacitor discharges in order to time an output signal of the first and second comparators.

3. The temperature monitoring device according to claim 2 wherein the first comparator provides an ambient temperature output signal to a first input of the controller when the voltage potential signal applied to the first comparator from the capacitor falls below a voltage potential temperature signal applied to the first comparator from the ambient temperature sensor, and wherein the second comparator provides a charger terminal temperature output signal to a second terminal of the controller when the voltage potential signal applied to the second comparator from the capacitor falls below a voltage potential temperature signal applied to the second comparator from the terminal temperature sensor.

4. The temperature monitoring device according to claim 1 further comprising a first resistor and a second resistor, wherein the ambient temperature sensor and the first resistor make up a first voltage divider network and the terminal temperature sensor and the second resistor make up a second voltage divider network, and wherein the temperature signal from the ambient temperature sensor is a voltage potential signal from a node between the first resistor and the ambient temperature sensor and the temperature signal from the terminal temperature sensor is a voltage potential signal from a node between the second resistor and the terminal temperature sensor.

5. The temperature monitoring device according to claim 1 wherein the controller determines the temperature of the battery pack by the equation:

space="preserve" listing-type="equation">T.sub.BATT =C.sub.1 T.sub.1 +C.sub.2 T.sub.O +C.sub.3 T.sub.A +C.sub.4

where,

T_BATT is the temperature of the battery pack;

T₀ is the temperature of the charging terminal before the battery pack is inserted into the charging device;

T₁ is the temperature of the charging terminal after the battery pack is inserted into the charging device; and

T_A is the ambient temperature within the battery charger.

6. The temperature monitoring device according to claim 1 wherein the controller converts an internal frequency clock to counts so as to time a discharge of the capacitor to determine the ambient temperature and the temperature of the terminal, said controller converting the frequency clock counts into logarithmic analog-to-digital clock counts.

7. The temperature monitoring device according to claim 1 wherein the ambient temperature sensor and the terminal temperature sensor are thermistors.

8. The temperature monitoring device according to claim 1 further comprising a sensor wire connecting the terminal sensor to the temperature monitoring circuit, said controller determining whether the sensor wire is broken.

9. The temperature monitoring device according to claim 8 wherein the controller determines whether the sensor wire is broken by determining whether the charging terminal is continually maintained at a minimal temperature and whether the ambient temperature is greater than a second minimum value within a predetermined time interval.

10. A temperature monitoring device for determining the temperature of a battery being charged in a charging device, said monitoring device comprising:

a temperature sensor positioned relative to the charging device and providing a temperature signal; and

a temperature monitoring circuit responsive to the temperature signal from the temperature sensor, said temperature monitoring circuit including a comparator and an RC circuit having a capacitor and a resistor, said temperature signal being applied to one terminal of the comparator and a known voltage potential signal from the capacitor being applied to another terminal of the comparator, said temperature monitoring circuit removing the known voltage potential signal from the capacitor to cause the capacitor to discharge through the resistor so that the voltage potential signal applied to the terminal of the capacitor decreases, said comparator providing an output signal indicative of the sensed temperature when the voltage potential from the capacitor falls below the temperature signal from the temperature sensor.

11. The temperature monitoring device according to claim 10 further comprising a voltage divider network, said voltage divider network including the temperature sensor and a resistor, wherein the temperature signal from the temperature sensor is a voltage potential signal from a node between the resistor of the voltage divider network and the temperature sensor.

12. The temperature monitoring device according to claim 10 further comprising a controlling device, said controlling device applying the known voltage potential signal to the capacitor, said voltage potential signal from the controlling device charging the capacitor so as to provide the known voltage potential signal to the comparator from the capacitor, wherein the controlling device removes the voltage potential signal from the capacitor so as to allow the capacitor to discharge, said controlling device providing counts at an internal clock frequency as the capacitor discharges in order to time an output signal of the comparator and convert the frequency clock counts into logarithmic analog-to-digital clock counts.

13. The temperature monitoring device according to claim 12 wherein the comparator provides a temperature output signal to an input of the controlling device when the voltage potential signal applied to the comparator from the capacitor falls below the voltage potential signal applied to the comparator from the temperature sensor.

14. A method of controlling a battery charger for charging a battery having at least one battery cell, said method comprising the steps of:

monitoring ambient temperature in the vicinity of the battery charger;

monitoring the temperature of a terminal of the battery charger, said terminal electrically connecting said battery to said battery charger;

processing an ambient temperature signal and a terminal temperature signal to provide an output indicative of the ambient temperature and the battery temperature, said step of processing including applying the ambient temperature signal to a first comparison system, applying the battery temperature signal to a second comparison system, and applying a known voltage potential signal to the first and second comparison systems, said known voltage potential signal being caused to decrease so that when the decreasing voltage potential signal falls below the ambient temperature signal, the first comparison system provides a first output signal, and when the decreasing voltage potential signal falls below the battery temperature signal, the second comparison system provides a second output signal;

using an algorithm to combine the ambient temperature and the terminal temperature to infer a temperature of the battery cell; and

controlling said battery charger in response to said inferred temperature on said battery cell.

15. The method according to claim 14 wherein the step of using an algorithm includes using the algorithm:

space="preserve" listing-type="equation">T.sub.BATT =C.sub.1 T.sub.1 +C.sub.2 T.sub.O +C.sub.3 T.sub.A +C.sub.4

where,

T_BATT is the temperature of the battery;

T₀ is the temperature of the charging terminal before the battery is inserted into the charging device;

T₁ is the temperature of the charging terminal after the battery is inserted into the charging device; and

T_A is the ambient temperature within the battery charger.

16. The method according to claim 14 wherein the step of monitoring ambient temperature and monitoring temperature of a terminal includes the use of thermistors as temperature sensors.

17. A battery charger for charging a battery, said battery charger comprising:

a first temperature sensing device for sensing the temperature of the battery;

a second temperature sensing device for sensing ambient temperature in the battery charger;

a temperature monitoring system responsive to temperature signals from the first and second sensing devices, and providing output signals indicative of the temperature signals, said temperature monitoring system including a first comparison system for comparing a voltage potential signal from the first temperature sensing device to a known voltage signal, and a second comparison system for comparing a voltage potential signal from the second temperature sensing device to a known voltage signal; and

a controller responsive to the output signals from the temperature monitoring system, said controller controlling the known voltage potential signal that is applied to the first and second comparison systems.

18. The battery charger according to claim 17 wherein the first temperature sensing device is a thermistor bonded to said terminal and the second temperature sensing device is a thermistor attached to the charger.

19. The battery charger according to claim 17 wherein the temperature monitoring system includes a first comparator, a second comparator and a capacitor, said first comparator being responsive to the voltage potential signal from the first temperature sensing device, said second comparator being responsive to the voltage potential signal from the second temperature sensing device, and both the first and second comparators being responsive to the known voltage potential signal from the capacitor.

20. The battery charger according to claim 19 wherein the first comparator provides an ambient temperature output signal to a first input of the controller when the known voltage potential signal applied to the first comparator from the capacitor falls below the voltage potential signal applied to the first comparator from the ambient temperature sensor, and wherein the second comparator provides a charger terminal temperature output signal to a second terminal of the controller when the known voltage potential signal applied to the second comparator from the capacitor falls below the voltage potential signal applied to the second comparator from the terminal temperature sensor.

21. The battery charger according to claim 17 wherein the controller determines the temperature of the battery by the equation:

space="preserve" listing-type="equation">T.sub.BATT =C.sub.1 T.sub.1 +C.sub.2 T.sub.O +C.sub.3 T.sub.A +C.sub.4

where,

T_BATT is the temperature of the battery;

T₀ is the temperature of a charging terminal before the battery is inserted into the charging device;

T₁ is the temperature of the charging terminal after the battery is inserted into the charging device; and

T_A is the ambient temperature within the battery charger.

22. The battery charger according to claim 17 further comprising a first resistor and a second resistor, wherein the first temperature sensing device and the first resistor make up a first voltage divider network and the second temperature sensing device and the second resistor make up a second voltage divider network, and wherein the temperature signal from the first temperature sensing device is a voltage potential signal from a node between the first resistor and the first temperature sensing device and the temperature signal form the second temperature sensing device is a voltage potential signal from a node between the second resistor and the second temperature sensing device.

23. A temperature monitoring device for determining the temperature of a battery being charged in a charging device, said monitoring device comprising:

a temperature sensor positioned relative to the charging device and providing a temperature signal;

a temperature monitoring circuit responsive to the temperature signal from the temperature sensor, said temperature monitoring circuit including a comparator and an RC circuit having a capacitor and a resistor, said temperature signal being applied to one terminal of the comparator and a voltage potential signal from the capacitor being applied to another terminal of the comparator, said comparator providing an output signal indicative of the sensed temperature; and

a control device responsive to the output signal from the comparator, said control device switching a voltage potential signal to the capacitor to charge the capacitor and provide the voltage potential signal to the comparator from the capacitor, said control device removing the voltage potential signal from the capacitor so as to allow the capacitor to discharge, said control device providing counts at an internal clock frequency as the capacitor discharges in order to time an output signal of the comparator and convert the frequency clock counts into logarithmic analog-to-digital clock counts.