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| Material | Calculation | Joules per Degree Celsius |
|---|---|---|
| 18650s | 41.5kg * 830J/kg K | 34 445 |
| Nickel | 0.8kg * 440J/kg K | 352 |
| EMS Sigma 60 | 1.54kg * 400J/kg K | 616 |
| TOTAL | ~35.5 kJ |
Looking at our temperature rise for a 75A discharge, we find that it takes roughly 1000 seconds to heat up the pack from 33 to 43 degrees Celsius. *This is only for 1 module, but the result can be scaled to the pack.
At around 75A, according to the battery heat production page, we are producing just under 330W of heat for the pack.
330W * 1000s = 330 000J
With our estimate of the specific heat capacity of 35.5kJ/deg C, 330kJ of energy should result in: 330kJ / 35.5kJ/deg C = 9.3 deg C.
| Discharge Current | Condition | Rate of Temperature Rise (degC / s) | Expected pack heat production | Calculated Specific Heat Capacity (J/deg C) |
|---|---|---|---|---|
| 75A | No Fan | 0.01041447 | 320.6W | 30 784 |
| 50A | No Fan | 0.00348684 | 142.5W | 40 867 |
| 100A | No Fan | 0.015011184 | 570W | 37 971 |
| 30A | No Fan | 0.001594079 | 51.3W | 32 181 |
Average Specific Heat Capacity from measured data: 35.45 kJ/deg C
So, the thermal mass of the pack being 35.5kJ/deg C is a very reasonable estimate.
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