MSXIV’s LG Chem MJ1 18650 batteries had an operating temperature range of 0 ~ 45°C for charging and -20 ~ 60°C for discharging. The internal temperature of the cells cannot exceed 45°C if they are to be charged by the solar array and regenerative braking. It is estimated that the average high temperature in the US Midwest will be around 35°C. Thus, sufficient cooling is needed to ensure the temperature of the cells does not exceed 45°C from the starting point of the ambient temperature of 35°C.
Temperatures above 45°C will force the shutdown of solar array charging and regenerative braking.
Temperatures above 60°C will lead to accelerated degradation.
Temperatures above 130°C have a risk of thermal runaway and explosion.
Optimal Discharge Temperatures
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There is only a 5% deficit of capacity from the optimal discharge temperature of 23°C to the max discharge temperature of 60°C. The difference in capacity is negligible so the focus of cooling system should be to maintain temperatures under 45°C.
Tab Cooling vs. Surface Cooling
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Tab cooled cells can last 3x longer than surface cooled cells due to more homogenous cooling across the cell but requires the need to electrically isolate the cooling system to prevent a short circuit of the pack and also to ensure that no failure of the cooling system at a joint results in the release of coolant into the battery pack itself.
Best case scenario: A cooling system that can match the heat output during peak currents + maintain uniform cooling throughout battery + that cooling capacity doubled for a safety factor of 2
Worst case scenario: A cooling system that can mitigate heat accumulation such that the battery reaches 45°C at end of leg