2x 12v 100ah in series different voltages

[SeanWatts]

I have 4x 12v 100ah batteries in 2s2p for 24v.

Today my inverter set off an alert, so I checked the battery voltages, and putting a volt meter on each battery, the voltage is different. On both of the 2s batteries that make the 24v one is 14.1 and the other is 13.3.

How is that even possible?

Two batteries are connected together to make 24v. Those two are connected in parallel. The positive term on the left pack goes to the + bus bar, and the negative on the right pack goes to the - bus bar. From those bus bars goes to two scc and the inverter.

All battery cables are 2awg copper.

The only thing I can think of is that the parallel + and - cables are not equal length. The - cable is longer.

 

[SeanWatts]

 

[Craig]

Ok so please report the voltage of each cell from left to right so we can get a better understanding but if I am looking at it correctly I can see all4 batteries being a different voltage.

 

[SeanWatts]

I have disconnected all batteries at the moment, but left to right was 14.1, 13.3, 13.3, 14.1.

 

[SeanWatts]

I disconnected everything and using a thinner gauge wire, I got them all to 13.48, and connected them all in parallel and let sit for 30 minutes. They all where at 13.48v, so I disconnected everything again, and wired them in 2s2p. Outside left is + and outside right is -. Hooked it back up to the bus that is connected two the scc and inverter. Turned everything back on, and it is doing the same thing. The outside two batteries are showing a higher voltage than the inside two.

If it was a bad connection, this difference would only show up in one of the 24v pairs, but it is both.

 

[Craig]

Well my first thing to try is putting them in 2p2s configuration. I would put a white with a black for each pair. I have no reason but it seems to me that there is something going weird with paralleling the 2 batteries after being in series. Was there a load or a charge going on while you were testing?

 

[SeanWatts]

Well my first thing to try is putting them in 2p2s configuration. I would put a white with a black for each pair. I have no reason but it seems to me that there is something going weird with paralleling the 2 batteries after being in series. Was there a load or a charge going on while you were testing?

I may try that. Yes, there was power coming in from the scc and going out through the inverter when testing the voltage.

 

[Craig]

I may try that. Yes, there was power coming in from the scc and going out through the inverter when testing the voltage.

This could have something to do with it. Test the cells with everything off if you can

 

[SeanWatts]

The sun is down now, so no power going in, and now all 4 batteries show 13.2v.

Was there nothing wrong to begin with, and only showing higher voltage on the outside two batteries because they are the ones connected to the scc?

 

[Craig]

The sun is down now, so no power going in, and now all 4 batteries show 13.2v.

Was there nothing wrong to begin with, and only showing higher voltage on the outside two batteries because they are the ones connected to the scc?

I do not know for sure but I am thinking it is something like that. Especially since both sets had the same voltages.