I'm having some trouble with two lithium ion packs that shut off too soon. One is a 9 Ah pack that shuts off after 2 Ah and a resting voltage of around 52. The other is a 12 Ah pack that shuts off around 9 Ah and a resting voltage of 47. They both had sat around for a while without being used, stored at full charge. The 9 Ah I balanced twice with an independent charger, and they both charge up to 54.3 volts. Is this fixable? I think the 9 Ah has been cycled about 200 times and the 12 Ah about 50, both over about 2+ years, though hard to say for sure how many times I don't keep track.
BMS shuts off far too soon on two Li ion packs
- Thread starter quuxman
- Start date
Alan B
100 GW
Are you able to measure the individual cell group voltages? Packs sound way out of balance.
So far I've only extracted the BMS on the 9 Ah, and yes the balancing is not surprisingly horrible. Two cell groups are at 3.6, the rest are overcharged to 4.3. Apparently my BMS is a POS. I hope that hasn't caused too much damage. I'm starting to think the BMS is causing me more problems than it's saving, and I wish I had a hobby-style 14 cell charger. I also wish I had a way to do a controlled discharge of the battery. I tried plugging it into a 100 watt incandescent bulb with 12.6 Ohm resistance, which I figured would draw about 4 amps from the battery, but nothing happened.
Alan B
100 GW
It is not uncommon for BMS to shut off at 4.3V per cell. Check the specs if you can. It might be working as designed.
BMS's generally have weak balancing function and depend on frequent full charge cycling to keep balancd. They cannot balance a pack quickly once it is way out.
You may find that balancing the pack with a good balance charger (like a BC168) will fix them and return them to "normal" operation. Perhaps. That's what I would try first. Get those cells down from 4.3 as soon as you can, and then get them all to 4.15 or 4.2 and then try the standard charge/discharge to see if they maintain.
All Packs really should have connectors on them for checking balance and re-balancing when needed, regardless of having a BMS. Unfortunately they don't do that.
The BMS may draw some power from the bottom cell groups, are they the low ones?
BMS's generally have weak balancing function and depend on frequent full charge cycling to keep balancd. They cannot balance a pack quickly once it is way out.
You may find that balancing the pack with a good balance charger (like a BC168) will fix them and return them to "normal" operation. Perhaps. That's what I would try first. Get those cells down from 4.3 as soon as you can, and then get them all to 4.15 or 4.2 and then try the standard charge/discharge to see if they maintain.
All Packs really should have connectors on them for checking balance and re-balancing when needed, regardless of having a BMS. Unfortunately they don't do that.
The BMS may draw some power from the bottom cell groups, are they the low ones?
999zip999
100 TW
A single cell charger. I have a voltpheak stops at 3.6v. I bet you can find one for your voltage.The point if using a cell phone like charger do check, because I read 5v on the side and it puts out 7v. Always check with multi meter. You must watch as it rises voltage climbs very fast at the end. Or don't walk away. Bms can just use first 2-3 cells. 3.5 volts on those cells is little harm.
Just balance.
Just balance.
I have a single cell charger already, because of this 9 Ah pack. After balancing it, I did an approximate 50% discharge on a ride, and thought I was good, but then on the next trip it started shutting off after 2 Ah or less, which is where I'm at now. Either I didn't balance it properly, or this pack needs to be rebuilt / retired.
For my next pack I'm planning on building, has anybody put together a BMS that actually keeps the cells balanced as well as a balancing charger? I imagine battery packs for cars are built this way.
For my next pack I'm planning on building, has anybody put together a BMS that actually keeps the cells balanced as well as a balancing charger? I imagine battery packs for cars are built this way.
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