I have my battery for some time now, I monitor often since, today when charging I noticed that one of the packs drops 1.5v, when the charging stops it comes back to normal. What could cause this? Please check attached photos
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The BMS might be faulty.
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Broken nickel strips associated with that P group and balance wire connection.
Make sure the battery and BMS is physically in good condition, check the voltage with a meter while charging, at the balance connector. Find out if the voltage at the BMS on that cell actually is going low. It’s either the BMS, the battery, or the software playing up. I doubt it’s the software if it used to work fine and nothing’s changed.
Also don’t slip or do anything dumb unless it’s the 5th of November.
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opened it up, cables look ok, to take a better look at balancing cables i have to tear down the wrapping. Voltage was dropping instantly for 1-2s and it came back to normal, i had 0.1-0.08 + on that pack for some seconds as well.
After it charge over 3.6V everything looks to come back to normal, delta is 0.01.
Thing is, if I stopped the charger, the voltage readings would be back to normal. Uff
@TimR
Later edit: I noticed that my charger wasn’t plugged in fully, i don’t believe this to be the cause but who knows
Sounds weird. If it were mine, I’d be tearing into it.
I often get asked if I have had a battery fire yet. The “yet” bit is the bit I don’t deal with too well, especially as all my batteries are from recycled scooters.
If the balance wire is high resistance, and the passive balance shunt comes on, that would cause the displayed voltage to drop but I would have thought it would fluctuate repeatedly between high and low voltage. An unlikely fault, but who knows.
Assuming the software is reporting correctly then there has to be something faulty.
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Thanks. Next step is to tear it down but I need to order some shrink wrap first. Will watch it closely from now on.
When putting the battery back, the drops started again. So my guess is that it’s the balancing wire, i’ve rode it 15 km and everything on the BMS was withing 0.01 delta.
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This looks like a bad balance wire. Needs to get fixed asap or the bms could read the wrong voltage and “balance “ one of the groups to death. Don’t charge it and pull that group apart or you may need to replace it. It could be just the balance cable is broken but held in by tape ir it could be the welds though if it was the welds you could be getting cutouts and other symptoms that you didn’t mention so probably not.
Fix it asap - no rides just incase it is the welds but definitely do not charge it until you find the break. I have run into a few cases of the balance wire at the solder joints breaking - the fis is to resolder it and put some adhesive on there at the joints and well down the wire to act as a strain relief to prevent flexing where the solder has wicked up into the wire. That point is weak and susceptible to vibration breaking it.
Hit it with some hot glue way back onto the wire to help with this
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As expected, it was a balancing wire. Soldered it back and it’s good.
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