Voltage irregularity

[-robw-]

Hi folks. I was surprised this morning when my battery alarm started beeping at 25.6v even though SOC was 45%, so I had a look:

I disconnected all interconnects and look voltages after an hour.

Would someone explain why these top 3 batteries have voltages between 13.05-07 and the lower 3 have voltages between 12.57-8? Lithiums are 2 years old. 24 volt interconnect is 2/0. Other interconnects are 4 AWG. Batteries are inside and all terminals are clean. The wiring should be perfect. 24 volt system. Thanks.

Batteries.png

[littleharbor2]

You need to use quality bus bars and equal length matching cables from each string

[-robw-]

Thanks. All interconnects are equal in length, as is all 3 wires coming off copper bus. Not sure that would be this issue though, as there is voltage consistency between the 1st batteries in strings and 2nd.

[-robw-]

Grok has recommended I reverse the positive and negative main lines to the 3 strings, thinking that the foot difference in those primary cables led to the imbalance (although that makes little sense to me). Have done so and will check voltages again in a month.

[SunEagle]

Parallel wired batteries run the risk of seeing different voltages even if the wiring is the same length.

[-robw-]

That's true, Suneagle, but what is most confounding in my observations is how the 1st batteries in the 3 strings are equal as are the 2nd batteries, but there's a large difference in voltages between that 1st and 2nd batteries in string. I've not seen that before, but then again these are my 1st lithiums (BMS?). I uploaded an edit of original image to clarify.
Batteries.png

[littleharbor2]

Lithium batteries have a tendency to diverge from one another Especially in parallel. The BMSS can't communicate between individual batteries and once they get a good size differential between them your charge controller is going to assume they're full when some of them are not full and others have higher voltage and are full and possibly even shutting down because they're full to the brim get yourself a battery balancer to go to each string of batteries and charge them all full reassemble them with a balancer and that should take care of you

New illustration was very vague as to what was going on there. I see no bus bar I see no equal cables and I see no indication of lithium batteries so hence the answer I gave before

[SunEagle]

That's true, Suneagle, but what is most confounding in my observations is how the 1st batteries in the 3 strings are equal as are the 2nd batteries, but there's a large difference in voltages between that 1st and 2nd batteries in string. I've not seen that before, but then again these are my 1st lithiums (BMS?). I uploaded an edit of original image to clarify.
Batteries.png

I stand by my answer. Batteries not wired in series can see different charging voltages especially if they are lead acid. If they are lithium they each must have a BMS (battery management system) to keep them balanced.

[littleharbor2]

I'd suggest you look into rewiring that battery bank. You have way too many connections including the two center batteries each have three lugs per post this is causing excess resistance and surely is contributing to your balance issues.

image.png

[-robw-]

Thanks. Yes, some lugs have 3 wires, but I have made sure to base the primary wires so that only the equalizing interconnects (which do a great job, as per voltage readings after 2 years) are stacked. I think I'd rather not add not only 3 balancers but also 3 equalizers, that's a bunch of add-on devices that could go bad. Adding 3 balancers alone is a great idea though. I thought the batteries BMS's would do that job without help but obviously that's not the case.

I like Victron, has anyone had a problem with their balancers? Are the .8 amps they push really going to make a difference with a 200ah string?

[-robw-]

Well, so much for that. Victron won't answer if their balancer works with lithiums, nor can their dealers I called, and every other balancer I see is Chinese - which is a nope from me. Also, per this image I guess only 1 balancer is required for my 3 strings? So that's .8a/3 or .27 amps per leg? How can that possibly correct 200ah strings?
victron.jpg

[bcroe]

Good advice above, I will add this. The problem could be one battery
is either under charged, or not capable of matching the other 5. I
would take them apart and try bringing each up to a charged state.
They should all end about the same, then try them together again.

If individual voltage of one does not match the others well, it might be
the problem. good luck, Bruce Rice

[-robw-]

Logical, which is why I isolated each battery and checked their voltages after an hour+. But that wasn't it, the top and bottom batteries were amazingly balanced among other 1st and 2nds in string.

After being dicked around around by victron and my having to find another solution, I realized a duh moment in thinking there was some difference between a balancer and equalizer. There's not. I found and ordered 2 equalizers pushing 10 amps that should resolve. It still would be nice to understand why this is happening but I guess commentary focused on how lithiums just do this will work.