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NiMH break-in charging
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IanB:

--- Quote from: pcm81 on January 01, 2023, 03:18:22 pm ---Has anyone seen a case where battery temperature goes up but -dV does not get triggered even though it should?
I am charging at 1.5A, have -dv set at -3mV and have few cells that terminate due to over-temp, set at 45C rather than due to -dv. Most cells terminate good at those same settings by -dV.

--- End quote ---

Generally, they would be bad quality or underperforming cells. They might be rescued by a break-in cycle (charging at 0.1C for 16 hours, discharging down to 1.0 V at 0.2C, then repeating). If they are not rescued this way, then you should probably put them in the reject pile. You don't want to use them.

This failure to terminate normally would tend to occur if the cells have an abnormally high internal resistance due to age (if old) or some problem in manufacture (if new). The minus dV will only occur if the cell is fully charged at the time the temperature goes up. If the temperature starts to go up before the cell has reached a full charge then the voltage will continue to rise due to charging and the over temp limit will be reached first. Cells like this with a high internal resistance will not only fail to charge normally, they will also have poor performance in a battery.

It goes without saying that when selecting cells for a battery pack you want to reject any cells like these that do not perform to a good standard.
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