Help Diagnosing BMS failure

Batteries, Chargers, and Battery Management Systems.
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DrInnovation
100 W
100 W
Posts: 115
Joined: Jul 28, 2014 7:27 pm
Location: Colorado Springs, CO

Help Diagnosing BMS failure

Post by DrInnovation » Jan 14, 2018 10:53 pm

My BMS has failed (and took a headway cell with it). There was a broken sense wire as well so not sure if that cause it or happened when I disassembled the pack. Normally I plug the bike in every day (its my daily commuter). The bike was working fine before vacation but I left it unplugged as we were going to be away for 12 days. When I returned the battery was dead. Disassembled it and a cell was dead. I got a replacement cell charged to 3.36 (about what the other cells were at). I replaced the cell and rewired the sense wires and hooked things back up. The BMS LED lit up instantly. I checked, cell was still at 3.35. Not being sure what the BMS cut off was, I let it sit on the BMS a bit while I was checking all the other cells and sense wires were connected. After about 15min the cell was down to 3.3, and everything else was correctly set. I'm guessing something is bad on a voltage sensing circuit or something else in the BMS circuit.

Pictures below. Include some where one can read the chip numbers.
Bottom two rows of chips on front seem to beEL817 series Photo-coupler, so not likely them.
The big chip on the back seems to be a TI quad nan gate, so not likely the issue if only 1 channel is misbehaving.
Small 6-pin chip on the back is label 361A.. no manufacture and so I don't know what it is. From its placement on the circuit I'd guess its a voltage comparator or something, and likely the culprit, but cannot really debug it without knowing what it is.


Any tips how to diagnose this?
Attachments
BMS-20180114_164752.jpg
Closeup of chips where you can see part #.
BMS-LED_20180114_164556.jpg
Pic showing LED lit.
20180114_164556.jpg
Overall Pic of board -- I don't know the model.
20180115_083557.jpg
Back Chip (Voltage Comparator?)
20180115_083557.jpg (220.59 KiB) Viewed 98 times
20180115_083539.jpg
Back Chip
20180115_083539.jpg (150.77 KiB) Viewed 98 times
20180115_083353.jpg
Back of board
Back of Board
20180115_083353.jpg (211.62 KiB) Viewed 98 times
Owner of a Crystalyte 4012/409 with 10aH 16s Headway on a old huffy frame. Its not fast but it climbs my daily commute up 8% and 10% grades nicely. Previous bike was a 24v Lashout 600w with RCLipos but I kept blowing the gears. I upgraded that one to a front-drive hub with a home-built 18650-based 20ah-36v. My bigger "E-ride" is a chevy volt.

User avatar
DrInnovation
100 W
100 W
Posts: 115
Joined: Jul 28, 2014 7:27 pm
Location: Colorado Springs, CO

Re: Help Diagnosing BMS failure

Post by DrInnovation » Feb 09, 2018 11:24 am

Well with a good bit more searching I still did not anything about the unknown 361A chip, so ordered a different model of BMS to replace it. Still hoping I can fix this as a backup so any tips/ideas welcome. Anyone with an old dead BMS with that part on it they want to get rid of I'll cover postage and maybe small$ for the parts.
Owner of a Crystalyte 4012/409 with 10aH 16s Headway on a old huffy frame. Its not fast but it climbs my daily commute up 8% and 10% grades nicely. Previous bike was a 24v Lashout 600w with RCLipos but I kept blowing the gears. I upgraded that one to a front-drive hub with a home-built 18650-based 20ah-36v. My bigger "E-ride" is a chevy volt.

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