Method and apparatus for regulating charging of electrochemical cells using cell temperature increase rate
View Patent ↗A rechargeable electrochemical cell charging system is provided having a thermistor that engages the negative cell terminal at a location remote from the negative charge contact. The thermistor outputs temperature data to a controller in the charger that determines the rate of cell temperature increase. When the increase reaches a predetermined predetermined rate, the charge to the cell is discontinued. The cell can also include an air moving system that circulates cool ambient air through battery compartment to cool the batteries being charged.
1. A charger of the type that delivers a charge to an electrochemical cell, the charger comprising:
a controller;
at least one battery compartment that receives the electrochemical cell, the battery compartment including:
a positive charge contact engaging a positive cell terminal of the electrochemical cell;
a negative charge contact engaging a negative cell terminal of the electrochemical cell; and
a thermistor engaging the negative cell terminal at a position remote from the negative charge contact, wherein the thermistor provides data output to the controller for determining a temperature rate increase of the cell.
2. The charger as recited in claim 1 , wherein the thermistor provides data output to the controller for detecting a temperature rate increase of the cell.
3. The charger as recited in claim 2 , wherein the controller is in communication with the charge contacts and terminates cell charging when the thermistor indicates a measured cell temperature increase rate beyond a predetermined rate.
4. The charger as recited in claim 3 , wherein the predetermined rate is between 1 and 5 degrees C. per minute.
5. The charger as recited in claim 4 , wherein the predetermined rate is substantially 2 degrees C. per minute.
6. The charger as recited in claim 3 , wherein the controller is configured to apply a maintenance charge to the cell after cell charging has been terminated.
7. The charger as recited in claim 2 , further comprising a resilient support member disposed inside the battery compartment biasing the thermistor into engagement with a negative end of a cell disposed in the battery compartment.
8. The charger as recited in claim 2 , wherein the charger further comprises a housing, wherein the controller and battery compartment are disposed in the housing.
9. The charger as recited in claim 2 , wherein the thermistor is offset from the negative charge contact a distance of at least 0.5 mm.
10. The charger as recited in claim 2 , further comprising an air moving system including an air mover that causes ambient air to be delivered to the electrochemical cell.
11. The charger as recited in claim 10 , wherein the air moving system further comprises a vent disposed proximal the electrochemical cell that receives the ambient air.
12. The charger as recited in claim 11 , wherein the air mover creates a negative pressure at the vent to draw ambient air around the cell.
13. A charger of the type that delivers a charge to an electrochemical cell, the charger comprising:
a housing;
at least one battery compartment disposed in the housing that receives the electrochemical cell wherein the battery compartment includes a positive charge contact and a negative charge contact;
a controller;
a thermistor located within the battery compartment at a position remote from the negative charge contact; and
an air moving system including a vent disposed proximal the electrochemical cell, and a forced air source that draws ambient air into the vent.
14. The charger as recited in claim 13 , wherein the positive charge contact engages a positive cell terminal, and the negative charge contact engages a negative cell terminal.
15. The charger as recited in claim 14 , wherein the thermistor provides data output to the controller for determining a temperature rate increase of the cell.
16. The charger as recited in claim 15 , wherein the controller is in communication with the positive charge contact and the negative charge contact and terminates cell charging when the thermistor indicates a measured cell temperature increase rate beyond a predetermined rate.
17. The charger as recited in claim 16 , wherein the predetermined rate is between 1 and 5 degrees C. per minute.
18. The charger as recited in claim 17 , wherein the predetermined rate is substantially 2 degrees C. per minute.
19. The charger as recited in claim 16 , wherein the controller is configured to apply a maintenance charge to the cell after cell charging has been terminated.
20. The charger as recited in claim 16 , further comprising a resilient support member disposed inside the battery compartment biasing the thermistor into engagement with a negative end of a cell disposed in the battery compartment.
21. The charger as recited in claim 13 , wherein the controller is disposed in the housing.
22. The charger as recited in claim 15 , wherein the thermistor is offset from the negative charge contact a distance of at least 0.5 mm.
23. The charger as recited in claim 13 , wherein the forced air source pushes air out of the vent.
24. A method for determining a charge termination point, the method comprising:
connecting a positive positive cell terminal and a negative cell terminal of an electrochemical cell to a positive charge contact and a negative charge contact, respectively, of a battery charger;
applying a charge to the cell via the positive charge contact and the neciative charge contact;
measuring a cell temperature at the negative cell terminal of the cell using a thermistor engaging the negative cell terminal, wherein the thermistor is located at a position within a battery compartment of the battery charger remote from the negative charge contact; and
discontinuing the applied charge when a cell temperature increase rate greater than a predetermined threshold is measured.
25. The method as recited in claim 24 , further comprising the step of coupling a controller to the thermistor, the positive charge contact and the negative charge contact, and causing the controller to discontinue the applied charge when a cell temperature increase rate greater than a predetermined threshold is measured.
26. The charger as recited in claim 24 , further comprising biasing the thermistor into engagement with the negative cell terminal of the cell.
27. The charger as recited in claim 24 , wherein the predetermined threshold is between 1 and 5 degrees C. per minute.
28. The charger as recited in claim 27 , wherein the predetermined threshold is substantially 2 degrees C. per minute.
29. The charger as recited in claim 24 , further comprising applying a maintenance charge to the cell after discontinuing the applied charge when a cell temperature increase rate greater than a predetermined threshold is measured.
30. A method of cooling a rechargeable electrochemical cell in a battery charger, the method comprising:
placing the rechargeable electrochemical cell comprising a positive cell terminal and a negative cell terminal in the battery charger, the battery charger comprising a controller and at least one battery compartment that receives the rechargeable electrochemical cell, the battery compartment comprising a positive charge contact engaging the positive cell terminal; a negative charge contact engaging the negative cell terminal; a thermistor engaging the negative cell terminal at a position remote from the negative charge contact, wherein the thermistor provides data output to the controller for determining a temperature rate increase of the cell; and air-moving means attached to at least a portion of the battery charger; and
moving air across at least a portion of the electrochemical cell by said air-moving means, thereby cooling the rechargeable electrochemical cell.