Mr. Mik wrote:For testing purposes you might want to add insulation to the cells, so that you can measure heat production, rather than just the result of heat production minus heat dissipation.
That can give clues for what sort of thermal management or forced air cooling might be needed for a fully constructed pack.
It is also important to continue measuring heat after the end of testing; in my experience the surface of the Vectrix NiMH cells reach peak temperature well after the end of a test (or recharging); that's because it takes time for the heat generated in the cell center to spread evenly.
Depending on physical characteristics of different cells they might also have different "thermal mass"; that means that although they might have the apparent same temperature, one type might contain a lot more heat than the other. That will make a difference when repeated charge/discharge cycles are needed in very warm or very cold weather.
A battery with a higher thermal mass will initially appear to heat up less, but it will also remain warmer for longer, and might accumulate heat if not cooled for extended periods after riding and / or charging.
+1 on that Mr Mik!
I know about thermal management of lithium cells and the heat increase after the end of discharge was also observed but not as much as i expected.. thatS, around +2 to +5 degree max..
I also can add that at Constant Current discharge the voltage decrease as the cell discharge... and having the same current with lower voltage mean an increase of the IR wich indicate an increase of Heat production enevthou the voltage is lower for the same current.
I agree on the fact that testing a single cell without any other around it is not a as representative as a, ebike pack. But cell in the middle always get warmer than the surounding cells.. So wich condiytion is the best.. a tradeoff between these cell position?.... Also the discharge i dot was done in continuous current discharge wich not represent the same use than an ebike that is more like pulsated discharge peak with a minimum discharge rate...
Discharging by pulse current help the cell to dissipate the heat better eventhough the mean current is the same in both test.
For that maybe i'll upgrade my next test to see if there uis a real difference and if the heat still increase for 2 to 5 degree after the cell discharge cut.
I think this is difficult to reproduce the same conditions of use of ebikes battery discharge. some pack are made in cube.. or prismatic, some are plane shared in many small pack... some have air blowwing on them some have not...
So for that i think keeping the cell alone for the test is the most easy way to keep a baseline for compare cells..
Adding the projected proportional heat increase to the results for every different battery construction way is still the best i think.
Trying to imitate one perticular type of battery construction for a cell test might complicate the comparaison for the overall battery construction comparaison..
At least that's what every mechanical engineer heat simulation do.. they try to keep the baseline conditoins on their test methods and then they add the different test conditions to every simulations.