Need help with Overkill Solar BMS

[Gunnar]

OK, so I had my setup running for over a year with no issues. It's two 560ah batteries (eve cells), run in parallel with an Overkill solar 120amp 12v bms on each battery. Last fall, my inverter started kicking out on charging, and inverting. Just a few times, and I thought my inverter was going out. Got my trailer out of storage last month to try and see just what was going on with the inverter, since it can log everything to an SD card. Well, it wouldn't invert for more than a few seconds, but would charge OK. Weird. So I look at my bms app, and one bms doesn't show any current, charging or inverting. Aha. It's kicking out for overcurrent on the one working bms. I need about 140 amps to run the micro. So it was the one bms going out last fall, and now it completely died. Or so I thought. Ordered a new bms, and just installed it, and I am getting the same thing. I did reuse the balance wires from the old bms, and it shows the voltage of the cells. The other weird thing is, even though it says it's not got any current, the cells voltage go up when charging. One last note, the working bms shows 140 amps on it when inverting, so it's just not that the bad bms isn't reading current.

Anybody that can help, it is greatly appreciated!

 

[Gunnar]

Just to add a little more info - saw that overkill had someone hook up just the bad bms, so I did. It works fine. As soon as I hook the second one back up, it stops working again....

 

[HRTKD]

Each battery is 2p4s?

Have you checked the voltage of each cell individually with a voltmeter?

 

[Gunnar]

Each battery is 2p4s?

Have you checked the voltage of each cell individually with a voltmeter?

Yes 2p4s each battery. Voltage checks out fine.

 

[JJJJ]

This is a wild guess. I was having problems with the Bluetooth module and it stopped transmitting. Probably not that simple.

 

[HRTKD]

Can you clarify? If you run with just one BMS, either one, it runs OK. But when both BMS are in the circuit it fails?

 

[HRTKD]

I recall a vague reference to the BMS acting funny when the Bluetooth was wonky. Pull the Bluetooth cable out of the BMS and retest.

 

[Gunnar]

Can you clarify? If you run with just one BMS, either one, it runs OK. But when both BMS are in the circuit it fails?

Yes. Either one works fine on its own, but if I connect both, one doesn't pass current. It's the same one every time, and I bought a new bms, and it does the same thing.

 

[JJJJ]

How are your individual cell multimeter readings? Have you tried a full charge discharge cycle on each individual battery?

 

[HRTKD]

Yes. Either one works fine on its own, but if I connect both, one doesn't pass current. It's the same one every time, and I bought a new bms, and it does the same thing.

Don't reuse the balance charge wires or the connector. Maybe that's the problem.

 

[JJJJ]

The reason I asked my previous question is to see if internal resistance may be interfering with equal charging. I agree about the recommendation to change the harness. It is best to rule out the simpler things first and a bad harness or terminal connection can make for a bad day.