Smart ANT BMS incorrect cell voltage causes shutdown

Hello guys

At first I thought it was my own doing of not having my cells balanced or tightened properly that led to one or 2 cells misbehaving (even on discharge) last night when our power went off within 30 seconds I could hear the BMS peep and a few seconds later it disconnected the pack.

I checked on the ANT BMS iOS App and cell 6 was reporting 3.02V (IIRC) about 250mV lower than the other cells but when I tested it with my multi meter it was showing 3.27V
My next port of call is confirming my multimeter is reading correctly, if you guys have any suggestions on fixes I can try I am all ears, if its the BMS itself then it will be a little disappointing since its not even a year old.

Cheers!

Yeah, I have same drama with one cell. Have to give it a lot of TLC till it is balanced with the rest again.

I have two multimeters by now. I bought a fairly inexpensive clamp meter a while ago, and it came with probes and extra features. So I can usually compare at least one with the other. The odds of two multimeters (even cheap ones) being bad in exactly the same way is just about zero :slight_smile:

Yeah that’s what I thought as well, I will test every cell tonight with a extra multimeter I have here at the office, if it too picks up the difference I will probably disassemble the pack check the soldering work on the BMS lugs, clean off all the contact points and try again?

My problem is not with a cell being low (well TBC)
Either the BMS or my multimeter needs replacing, one of them got this wrong by about 250mV :slight_smile:

Dry joint on the BMS board perhaps. Break in the wire. Ideally, if possible, I’d like to measure the voltage at the joint on the board and also compare to at the battery.

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You need one more Plonkster :wink: hahahahah!!! well, that nice scope unit of yours can count as a 3de one. I got 3 multimeters and the one I use the most is my Fluke V88. Will love to get scope Oscilloscope and to learn how to use it.

To add to what plonkster is saying, check your crimping joint where the wire is going in to the lug and where the lug connect on top of the bush bar and battery, I had a problem like this a while ago where the crimp was lekker and with bush bars starting to oxide lightly. I cleaned it and sprayed some q20 to film the copper with oil.

Other option is to get lifpo4 charger to and to charge that cell in your lifepo4 bank to check what is doing and to see if the reading is picking up on the smart ant bms screen and your multimeter and what the charger screen reading is.

One simple way to check your multimeter is to see how it’s measurement compares to the BMS on other cells as well. i.e. Not just the cell with a low voltage reading on the BMS. If it is reading 250mV high on all the cells then it could be the multimeter. If it is only reading high on that one cell then it is certainly the BMS.

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