What portion of cells in the pack are at significantly higer SoC? I assume it is a small portion, or you would be individually charging the smaller portion of cells which are at lower SoC. I've done both. For higher SoC cells I connect a 3 Ohm 10W resistor between the terminals with spring clips so it shunts more current once the red LED lights on the minibms. This usually keeps it from going over 3.55V while the other cells are charging, but if you have severe imbalance it may not keep it below that voltage long enough for the others to charge up. In that case I stop charging the pack and continue bleeding the high cell for "a while" which is a guess at how many Ah I need to remove from it. I put the resistor inside a piece of pvc pipe so it is suspended inside by the wires, not touching the pipe since it gets fairly hot. Pipe ends are left mostly open for some ventilation. The timer would be a good safety device, but its setting is still just a guess for how long you need to discharge. Might be too long or too short. I like to just monitor cell V with a DVM. I have discharge curves I took years ago using a celllog8, so I have some idea of how much charge I need to remove to bring that cell into balance - but only roughly since the cells vary in V versus SoC. I hang a kitchen timer/alarm around my neck to remind me to check every x minutes, depending on how severe the imbalance is.
I've also done the converse, charging individual cells with a DC voltage supply. After charging the higher SoC cells fully (to 3.5V for me), I set the supply to 3.5V and let it charge each low one, one at a time. Don't have to watch it like you do bleeding with a resistor since it won't charge above 3.5V, but it lowers current as it approaches that value so can take several hours to charge a cell if it is at significantly different SoC than the others. I've only had significant imbalance like this when changing from no bms to the minibms years ago, or when replacing a cell. Since I don't have to watch charging with the DC supply, I found it easier to just leave the 3 Ohm resistor on the high cell long enough to bring it below the other cells in SoC, then charged the pack, then individually charged that cell. -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Suitable-Load-tp4678485p4678511.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 Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
