The specific heat capacity is a measure of how much energy is necessary to raise the temperature of a system a given amount. A system with a higher specific heat capacity is said to have a higher thermal mass, meaning that with the same amount of heat, it will have a lower temperature rise.
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So, the thermal mass of the pack being 35.5kJ/deg C lines up with the testing results pretty much perfectlywell within margin of error.
With this heat capacity of the pack, we are able to calculate some of the transient effects of going up hills, etc. Our strategy lead (Clarke) says that while going up a hill, a 10kW power draw for 5 minutes would be a conservative estimate for the length of a hill.
At 10kW, we are drawing 76A at nominal voltage and producing 329.2W of heat.
1W = 1J/s
329.2J/s * 5min * 60sec/min = 98.76kJ
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This discussion is continued on the Battery Pack Temperature Distribution page.
Also to note, is that with a constant 20A draw and 22W of heat production, we can figure out how long it will take to reach the max temperature, assuming we start at 35 degrees ambient, we would be looking for a temperature rise of 10 degrees (up to 45 degrees).
35.5kJ/degC * 10degC = 355kJ
355kJ / 22J/s = 16 000 s
16 000s / 3600s/h = 4.4h
With no cooling and a 22W rate of heat production, it will take 4.4h to raise the temperature of the pack by 4 degrees. So we will definitely need to cooling the pack at least a little during the 8h days on the track or the roads.