I have 132 60AH batteries in 2P66S. So I am going to call this 66 batteries at 120AH. Specs call for 3.6 volts max, so 66 in serial is 237.7 volts. I don't want to push them so I set the max voltage at 231volts charge which brings me to approx 3.5 volts per battery. Now in real life once it is at this 231 volts for the string each individual battery voltage is approx 3.34 volts +/- 0.10 volt. Even at the plus side of that each battery would be 3.44 volts or 227.04 volts for the string. So how is it that my charger string voltage is reading 334 - 335 volts while each battery is reading 3.34? Does it matter if the total voltage is over the max (66 X 231) as long as the individual voltage is less 3.5 volts? Should I set my BMS charge voltage cutoff higher and just leave each cell set at the 3.5 volts max.
You say that when you charge to 231V each individual pair of cells is actually at 3.34V +/-0.10V, so I assume you did indeed measure the voltage on all the pairs, and measured them with the same voltmeter you measured 231V with so if the voltmeter has some % error, it should be similar in both measurements. If so, there must be a source of resistance causing the voltage difference of about V = 231 - 66*3.34 = 10.56V near end of charge, or, perhaps you are measuring the cells' rest voltages a bit after charging, and not at the end of charge while the charger is still running? But then you say the charger reads 334 - 335V, which is way different than the 231V you say the string is at, so I'm confused. What charger are you using? Does it read 334 - 335V at the same time you measure 231V across the charger leads at the pack? -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/LiFePO4Charging-tp4671761p4671774.html Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com. _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
