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JBD, overkill, generic chinese 4s 80A BMS voltage goes crazy after periods of storage.

BoatGuy

New Member
Joined
Jan 9, 2022
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3
Hi All.
Hoping to ask for your help with my problem. I have built a 120 AH, 12v 4s Lifepo4 diy battery for deep cycle (trolling motor) use that is about 3 years old now. Sorry not solar but I am banking you guys know how to help.
The battery has been working fine but when I put it into storage (between fishing trips or over winter) the voltages displayed on JBD/overkill/Chinese (these all appear to be the same form factor) bms app (xiaxiong 3.1.1026) voltages go crazy. By crazy I mean all cells are happy...within say .05v for days or weeks. Then all of a sudden with no load BMS goes crazy (see pictures taken minutes apart with no load applied) and the bms shuts down and will not allow charge or discharge. Probing each cell they are all within .05v at the target 3.2v storage soc as measured with a multimeter.
If I can get it to accept a charge just a second or two and the bms returns to normal showing good and consistant values. (Back to 3.2 with .05 max deviation)
Do I have a faulty BMS or is this a known issue?
Since it's a pain to get inside the battery on the water I am thinking I may put a switch on the first (red) balance lead so I can "disconnect" the bms from outside the battery. Seems a disconnection reboots the bms and good values return. I've wired in a physical on/off switch to the bms but this doesn't power down the bms, just toggles discharge function so crazy remains. Anyone had this issue? Any issues with switching the balance lead on say a momentary push button...reset switch of sorts?

Thanks for your opinions and asssitance!
 

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I'm curious. If you go to the "Battery State" page, and then go to "Protection of information"(sic) on the 3rd tab within the Battery State page, does it show any fault types as non-zero? On first blush, this looks almost like your balance lead connector is loose, but I've not actually seen what you are describing. I have 2 4S 150A and 1 8S 100A running in my garage right now, and all are working great. The 8S 100A BMS has not been in storage per se, but it has not had any charge or meaningful discharge in about 3 months.
 
Thanks for the quick reply horsefly!

There are no faults currently showing as I just disconnected the balance cable to reset. Before that I believe I had both over and under voltage protections. Hence the inability to charge or discharge.
I will check the loop terminals on the balance lead to see if any are loose. Terminals are tight but wire crimps may not be....good suggestion.
Funny thing is the batter has been sitting in my basement for the last couple months....all good for a while then all of a sudden bad. It was not jostled or moved at all so finding it strange to be a loose connection as no physical disturbance would have jarred it free.
Ive had this issue for about 1 year now...coming and going. Disconnect and reconnect the bms seems to work every time, do you foresee issues with a push button on first cell positive? Wondering if neg balance cable may be better.

Thanks again for the thoughts...let me know if you have any additional suggestions.
Regards!
 
Ha good timing. To test horsefly's theory, I opened the app and started lightly tugging on each balance lead. All seemed secure but when I tugges on cell 3 the craziness began. I removed and replaced the ring terminal and now all things are good. If they go crazy again I will start pulling off the bus bars.

Thanks again for all the help guys. Hoping one poor crimp was causing my issue.
 
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