42
Cell Temperature
Ideally, the temperature of every series element or cell would be monitored by the BMS; however, it is not as
important as voltage, and is often impractical in cost-effective systems. A high-temperature condition is typically
the result of monitored voltage and current conditions either being out of bounds or caused by an external
thermal source. For such cases, monitoring a few representative places in a module or section of the battery pack
is adequate for proper battery pack management and cell protection. Thermocouples can be placed on a
representative worse-case cell’s surface to monitor its temperature (that is, the hottest cell in the pack).
Supervising Battery Pack Behavior
The circuitry that monitors the cells in a battery pack should also be used to supervise the battery pack
environment and use, to preserve the safety and life of the pack by protecting it from external fault conditions
such as overcharge, over discharge, overvoltage, undervoltage, over current and undercurrent. Methods of
supervising and controlling the battery pack include firmware based controls or special purpose integrated circuits.
Regardless of how the BMS supervises the pack’s behavior, protection from fault conditions should be its highest
priority function.
When monitoring cell behavior in the pack, histograms can be stored (e.g. saved in non-volatile EEPROM memory)
to record important details about the conditions that the pack saw while in service. This can be helpful in
troubleshooting problems and arriving at a root cause and corrective action if necessary. Suggested service
histograms are as follows:
•
Current and voltage
•
Representative cell temperature
•
State of Charge
•
Energy Throughput
Table 10 shows an example of temperature range and duration data derived from a service histogram.
Table 10 – Example of histogram data of temperature ranges and durations
Temperature Range
Duration (seconds)
< -20 °C
0
-21 – 0 °C
10
1 – 10 °C
110
11 – 20 °C
450
21 – 30 °C
70457
31 – 40 °C
5042
41 – 50 °C
250
51 – 60 °C
60
61 – 70 °C
10
> 70 °C
0
Similar data sets would also be stored for state of charge, energy throughput, voltages, and currents.
