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Issues with JK BMS

Diesel Pro

New Member
Jul 21, 2021
JK-B2A8S20P This unit has been in and working well for some time now, but recently I have had a couple of hiccups. The latest is that it said the sample resistance wire is to large and cut off the discharge. The previous time that I was up to visit it was in protect and I checked al the balance wires, reset it, and had issues with it shutting down when I switched on the inverter. I ended up turning off the breaker panel starting the inverter, then turning the panel (load) back on. All seemed well after this. The load in this case is pretty much nothing but some parasitic loads.

Balance wires all seem fine. Screen shots attached


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I would start by making sure all the connections associated with the balance wires are in good shape. Take it apart, inspect the connecting surfaces, clean them and reassemble. Check the cables to ensure that have been no cuts in them.
Try to remove and replace the balance lead plug from the bms. Also tug on the terminal eyelets, those are some of the worst things to crimp are those little balance leads. I’ve found those bad on factory batteries. I’ve got a special crimp tool just for those.
I'll have a look, but all was fine for a year and a half and if I reset it the resistance looks good. In the past I've seen odd alarms for cell over voltage also that did not show on the screen. Contemplating replacing the BMS. This is an unoccupied cabin so I'm only there briefly many times.
I have been finding that it shuts off on me when I am not there. The only way to get it to go is to switch off the load, then the charge controller will fire back up run. If I flip the load back on it shuts down. There were some odd errors a while back I think possibly about ARC but those screen shots are long gone now.

It seems to handle the inverter standby load fine, but does not want to run the super small standby load. It's frustrating to say the least. Either my battery bank is bad or the BMS is bad would be my guess. Voltages all show fine, but after I leave it shuts off. This time I left the panel off altogether and just the inverter.

I was unable to view the app due to phone issues and now I need to find the proper app for Android and load to my new phone.
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Just wanted to follow up. I did order a replacement BMS. I also went to work on the balance wires starting with the ring eye terminals right at the cells. I had good luck then it quit again. Then I remembered the responses here and unplugged then replugged the BMS end. Not sure the how and why, but it seems to be working now. It ran a few days without issue and also ran the microwave (inverter) for 3 cycles at 5 minutes each power level 5 without issue. Guess I will have a backup BMS.
And last visit the unit was shut down again. Pointing at Cells 1 and 2 balance wire resistance again. I restarted the BMS, disabled balancing, and we'll see what happens. Screen shot from before reset

Take the battery apart, moving the cells around. If the balance lead issue stays in the same positions then you probably don't have a cell issue.
Well what’s in common with before? The batteries(not the problem) and the balance harness. My guess is the connector in the harness has weak tension in #one or two sockets. When I install, I usually remove a few leads from the connector in case I messed up then cut off and seal the others that are unused. You can’t remove all the unused because the connector will pull out too easily from the bms. You could remove a few leads from the new harness by gently pushing down on the little tab and pull it out. You now have two leads to replace the two suspect in the old harness. Or you can just use the new harness. Be careful with loose ends around the top of those cells. Once the leads are connected to the cells then you can plug in to the bms.

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