Overkill BMS problem

[Bedhead122]

Newby here I have 4 batteries each with 8 cells 24V and 280ah all with Overkill 24V BMS.
1st battery BMS working fine. Everything looks accurate.
2nd battery shows 7 cells accurately. The BMS shows cell #7 at 0.47V and cell #8 at 5.867V these two voltages are in accurate all cells are approx the same.
Why would two cells voltages be showing wrong voltages?
Im pretty sure that the problem is something om doing wrong. I say that because I bought another BMS identical to the other 4 and when I hooked it up to that battery it gave me the same issue. I checked the wiring and it is correct same as the wiring on the battery that is accurate and works well.
I have been trying to make this work for weeks. I have all my solar panels installed and wired to the battery box. I'm so frustrated any suggestions or help finding the problem would be greatly appreciated.
Thanks in advance
Charles Ware.

 

[Tomthumb62]

The BMS shows cell #7 at 0.47V and cell #8 at 5.867V

So if you remove these cells from the pack and test with a a multimeter, what voltages do you get?

 

[rodrick]

Double check your wires you may have them crossed you can check at the connector that plugs into the bms it should start at 3.3 or close and go up the same approximately each pin until the 26-27 volts on the last pin

 

[SeaGal]

I have 3 suggestions...

1... like @Tomthumb62 said...

So if you remove these cells from the pack and test with a a multimeter, what voltages do you get?

But you can measure the cells with a multi-meter without removing them from the pack - a multimeter is isolated.

2... like @rodrick said, I suspect wrong wiring. (0.47V + 5.87V) / 2 is 3.17V which is a correct average voltage and probably not a co-incidence.
Hence - as you have more than one Overkill BMS, I'd swap just the BMS with a known working one (i.e. keeping the balance wires in situ) so just plugging the wires into the BMS connectors. If the problem remains with the battery pack, it's the wiring at fault. If the problem shifts to the previously working battery, it is the BMS at fault.

3... contact Overkill. They are known for good tech support.

 

[Topper]

"I suspect wrong wiring. (0.47V + 5.87V) / 2 is 3.17V "
I think we've all done this at least a couple times along the way. So easily done when wiring in small spaces.

 

[Brett V]

I concur with those who suggested you've miswired the BMS Tread lightly...you can easily destroy the BMS by connecting it wrong. Unplug the cable from the BMS, check and correct your wiring. then check battery voltages on the pins of the connector before plugging it in.

 

[Dynoman]

Newby here I have 4 batteries each with 8 cells 24V and 280ah all with Overkill 24V BMS.
1st battery BMS working fine. Everything looks accurate.
2nd battery shows 7 cells accurately. The BMS shows cell #7 at 0.47V and cell #8 at 5.867V these two voltages are in accurate all cells are approx the same.
Why would two cells voltages be showing wrong voltages?
Im pretty sure that the problem is something om doing wrong. I say that because I bought another BMS identical to the other 4 and when I hooked it up to that battery it gave me the same issue. I checked the wiring and it is correct same as the wiring on the battery that is accurate and works well.
I have been trying to make this work for weeks. I have all my solar panels installed and wired to the battery box. I'm so frustrated any suggestions or help finding the problem would be greatly appreciated.
Thanks in advance
Charles Ware.

Suggest leaving connector on BMS to cell leads disconnected until issue found on problem battery. I agree check the voltages on the cell terminals with a good volt meter after removing BMS connector. Should be able to leave cells connected when checking voltage. As stated Overkill solar has good support and will replace or refund the BMS even if you destroy it.

Check for a bad connection. This is probably the most common problem. Bus bars, wire lugs etc.

If certain wired correctly, check for a bad crimp on BMS leads lugs, or bent pins on BMS connector or messed up socket on BMS connector

As shown in Will's video check connector making good contact with all the pins using a voltmeter (starts at around 14:20). Be careful not to touch volt meter leads together when checking connector as this would short cell. If voltage not correct check continuity of wire(s) with ohm meter after disconnecting wire(s) from battery cell(s). I used this video when installing two 8s 24V 271ah cell batteries with 2 Overkill 24V BMS and found it very helpful. The fist half of the video he uses a 4s BMS on a 12 volt battery. Starting at around 12:40 he uses the 8s BMS on a 24 Volt Battery which is the part of the video I used. Suggest watching the entire video.

Also a link latest BMS manual from Overkill. Suggest reading if have not already.

8s BMS 100a LifePo4 with M6 Threaded Terminals – Overkill Solar

overkillsolar.com