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Battery balancing - when is it completely finished?


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Sorry if this has been addressed, but I couldn't find a definitive answer with a search so I thought I'd ask some of the experts here.

I have a Tesla V2 1500Wh, and I have two chargers for it: the 'stock' 1.5A charger (which I've measured the output to 84.2v, although it does move around a bit), and a cheap chinese 'fast' 5A charger (which seems only to output 3A max, and the output measures 83.7V). I also bought a Charge Doctor; I liked the idea of charging to 85% most of the time.

If I use the 'fast' charger, it will eventually charge to 83.6 volts, at which point it shows a green light and the charge doctor will settle down to 0.01A output. It will stay like that overnight; it never completely turns off, but the voltage does not increase either. The same is true for the 1.5A charger, although it will charge to 83.9V and stay there. EUC world shows 84.0V afterwards, so I'm not overly concerned about the last 0.1V difference; I'm sure that could be a difference in measurement accuracy anyway. But what I'm not sure of is, will the cells properly and completely balance at less than 84.0V (say, 83.6V)? And if they finally do, how will I know - will the CD show 0.0A? Do the chargers ever completely turn off? FWIW I measure about a 0.2V difference between what the CD shows (if it's only plugged into the EUC) and what I measure with my Fluke multimeter.

One last note; I've had a look inside the chargers, and the 5.0A charger doesn't seem to have any adjustment pots to increase the voltage output. The smaller (1.5A) charger does though, so I could increase that to a little higher voltage. Would that allow the BMS to 'decide' when it's completely balanced? That is, would there be any disadvantage of setting the charger to 84.4V or so? My understanding is that the BMS wouldn't allow the packs to actually reach that voltage anyway, but that they can't completely balance if the battery voltage doesn't actually reach 84.0V. Giving the charger a little extra output voltage would (in my mind) give the BMS a little extra to work with to ensure the packs are properly balanced. Does that sound reasonable?


Edited by Mantraguy
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