# Peukert effect during charge as well as discharge



## EVfun (Mar 14, 2010)

There is not really any Peukert's effect when charging. You have to replace the actual amp hours used plus 5 to 10 percent to make up for the charge efficiency being less than 100% for lead acid. If you amp hour counter is displaying a Peukert's adjusted amp hours available or percentage SOC then it is indicating you have removed more amp hours than you have actually removed. You will need some type of correcting factor to scale up the amp hours returned during charge. 

I feel it would be better to determine the actual amp hours you have available at EV discharge rates and enter than for the battery capacity and set the Peukert's exponent to 1.0 (no Peukert correction.) This will typically be only 50 to 60 percent of the nameplate capacity. The meter will scale your SOC based on that part of the capacity that is actually available. Since it will be showing actual amp hours you don't have to do any number fudging when you charge.


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## Siwastaja (Aug 1, 2012)

PStechPaul said:


> they [LiFePO4 cells] still have significant internal resistance which may affect the accuracy of SOC gauges using coulomb counting


Why would any internal (series) resistance affect coulomb counting?


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## PStechPaul (May 1, 2012)

Maybe LiFePO4 cells are different from other chemistries in this regard, but the portion of current that results in heating does not really contribute to the actual ampere-hours stored in the battery. I know that NiMH cells continue to conduct current at full charge and the result is a significant rise of temperature, and in lead-acid cells it results in heat and gassing. 

The effect is probably much less for lithium cells but I think a 10 Ah cell charged at 100 amps for 0.1 hour probably gets fairly hot and will have less capacity than the same cell charged for 10 hours at 1 ampere. If the internal resistance is 0.01 ohms (and no temperature coefficient), there will be 100 watts of heat at 100 amps, while only 10 mW of heat at 1 amp. And the energy loss will be 10 watt-hours compared to 0.1 watt-hours at the slower rate.

Rate of charge may only affect efficiency, which may not be a big deal, but there is definitely an effect on the life of the cells comparing charging rates of 10C, 1C, and 0.1C. The actual state of charge may not change much in these cases unless the cell is overcharged, in which case I think it will overheat and deteriorate rapidly, and at that extreme, coulomb counting will certainly be inaccurate.


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