C- on BMS reading 2.2V but B- reads 13.3V. Ideas?

[Dodging Normal]

Hey guys, been following the forum for a while but it's my first post. I am converting a camper van and have set up a temporary electrical system just to charge my tools and run a grinder and stuff, nothing over 4 amps 120V. I have a 4s2p (8 cells with 4 pairs) setup for now with an Overkill solar 12v (will change to a 2 bms later). I have only a Renogy 20amp B2B charger. I basically have not yet had the batteries fully charged, but I basically charge what I use each day.

My setup was working great for 2 weeks but yesterday my inverter wouldn't turn on. I checked the bms app and it was saying 13.3 volts with no issues. I checked the battery voltage on the actual battery and it was 13.3, but when I checked the battery voltage from the positive and the bms C-, I am only getting 2.2 volts. There is no warnings in the app, so I don't know if my bms is fried or what is going on.

Any ideas? Any help would be greatly appreciated. Let me know if you need more info, or a screenshot of the app. I have a lot of 12v automobile knowledge, but this is my first battery build.

Thanks,
Mike Dodge

 

[ereams65]

Have you tried reloading your app and reconnecting as new? I'd be curious to see if it continues to read that way, or if it's now just pulling up stored information.

 

[Dodging Normal]

Have you tried reloading your app and reconnecting as new? I'd be curious to see if it continues to read that way, or if it's now just pulling up stored information.

Thanks for the reply. I just deleted the app and it's data and redownloaded it. Same results, it says it's at 13.36volts.

 

[ereams65]

Sounds like your BMS is a problem. Connections are all good, I'm assuming? Any chance the C- wire got pinched and may have broken? Outside of having a bad meter, which is highly unlikely in this case, then I'm afraid you need a new BMS. Reach out to the guys at Overkill and explain whats going on. He's pretty good at responding.

 

[Dodging Normal]

Sounds like your BMS is a problem. Connections are all good, I'm assuming? Any chance the C- wire got pinched and may have broken? Outside of having a bad meter, which is highly unlikely in this case, then I'm afraid you need a new BMS. Reach out to the guys at Overkill and explain whats going on. He's pretty good at responding.

C- is good. It's reading 2.2V from each C-terminal, so no wire needed. The wires for the other ports look good. I was pretty meticulous with the wiring and it worked for 2 weeks. Not sure what would have caused it to fry, I was using less than 10ah per day. Maybe something happened with the Renogy charger. ?‍

 

[Bob B]

I think we need to see some screen shots from your App. All the data values and parameter values would be good.
Seems like the BMS has triggered a shutdown for some reason ... or has just gone bad.

 

[Dodging Normal]

I think we need to see some screen shots from your App. All the data values and parameter values would be good.
Seems like the BMS has triggered a shutdown for some reason ... or has just gone bad.

Thanks. Here is a screen shot before I re-installed the app. Again, I have not had a chance to do a full cycle until I get some solar or plug in battery charger.

 

[Pierre]

I am sure you have already unplugged / replugged the balance lead connector and shorted out B- to C- ?

 

[Bob B]

Thanks. Here is a screen shot before I re-installed the app. Again, I have not had a chance to do a full cycle until I get some solar or plug in battery charger.

I don't see anything in that screen shot that indicates it has shut down .... have you tried to toggle the battery on and back off?

 

[Bob B]

Actually, I do see that there is no temperature reading .... that is kinda odd. It doesn't show any temperature faults, but also no temperature value.

 

[HRTKD]

Actually, I do see that there is no temperature reading .... that is kinda odd. It doesn't show any temperature faults, but also no temperature value.

If the temp sensor isn't plugged in, the BMS assumes a very, very low temp and turns off charge/discharge.

 

[Bob B]

If the temp sensor isn't plugged in, the BMS assumes a very, very low temp and turns off charge/discharge.

Yeah .... that's what I would expect .... but in his picture there is no temperature reading at all .... and the system isn't showing a low temperature disconnect.

 

[Dodging Normal]

Yeah .... that's what I would expect .... but in his picture there is no temperature reading at all .... and the system isn't showing a low temperature disconnect.

Thanks for the replies guys! I don't know why the temp isn't showing in the screen shot. It has always worked and is currently working so I think that was just a weird fluke. It's working fine.

I did cycle the battery on and off. I skipped over the bms completely and my inverter turned on fine. I spent the last 2 hours double checking every connector with an ohm reader and went over the diagrams on Overkills instructions. I also unhooked every cell and have 3.3v on each. ?‍ Definitely thinking it's the BMS.

Let me know if you think of anything else but I guess I will have to contact support. I appreciate all the responses!

 

[HRTKD]

Such a low voltage on the output side makes me think the discharge circuit is OFF.