Battery pack thermistor test method
A battery pack thermistor test method includes charging a battery pack, monitoring a rise in average temperature reported by at least one thermistor on the battery pack over a predetermined time period, preparing at least one thermistor slope by calculating a least square fit of time vs. temperature for the at least one thermistor and comparing the at least one thermistor slope to process-defined thermistor slope limits.
1. A battery pack thermistor test method, comprising:
charging a battery pack;
monitoring a rise in average temperature reported by at least one thermistor on the battery pack over a predetermined time period following a start of said charging;
preparing at least one thermistor slope by calculating a least square fit of time vs. temperature for the at least one thermistor over a selected time period following said charging; and
comparing the at least one thermistor slope to pre-defined thermistor slope limits.
2. The method of claim 1 wherein charging a battery pack comprises applying a controlled charge profile to a battery pack cell in the battery pack.
3. The method of claim 2 wherein applying a controlled charge profile comprises applying a stepped current over a predetermined time period.
4. The method of claim 3 wherein applying a stepped current comprises applying a stepped current of constant durations over a predetermined time period.
5. The method of claim 4 wherein applying a stepped current of constant durations over a predetermined time period comprises applying a stepped current of constant durations of about 5.0 seconds each.
6. The method of claim 3 wherein applying a stepped current over a predetermined time period comprises applying a stepped current having a final step corresponding to a predetermined peak current.
7. The method of claim 6 wherein applying a stepped current having a final step corresponding to a predetermined peak current comprises applying a stepped current of about 10.0 seconds.
8. The method of claim 1 further comprising rejecting the battery pack if the thermistor slope falls outside the thermistor slope limits.