Help I have an unbalanced 2S3P 24V battery bank.

[Shadowhawk]

I have a System with 2S3P Lifep04 Batteries 4 have Bluetooth 2 do not. They are all purchased within 6 months of each other.
I have been having a problem with over volt on one side of my series connection, So i lowered my charge profile until I figure out a working solution.
Currently I am charging Boost/equalize at 27.6V and float at 27V on both controllers. This seems to have stopped the cell/battery over volt so far.
I am running an Ecoworthy 24v balancer and with 2p2s It was working perfect, once I added 2 more battery I started getting this issue.
So should I add a 2nd 24v balancer and run one on each end of the battery bank? Or should I have 3 of them one for each set? Or other idea that might help?
Any help will be appreciated.

This is my basic layout, batteries are not all Weize as stated above.

 

[sunshine_eggo]

Break your bank down and individually charge each to 14.4V for a couple hours. Then do it again in parallel. Then rebuild your bank.

12V batteries of any type must be fully charged individually and preferably again in parallel before using them to string into higher voltages.

 

[Shadowhawk]

Break your bank down and individually charge each to 14.4V for a couple hours. Then do it again in parallel. Then rebuild your bank.

12V batteries of any type must be fully charged individually and preferably again in parallel before using them to string into higher voltages.

Just got done doing that, I charged them 2 days at 12.8v and then lowered them a bit then charged at 14.4v for 24 hours.
I hooked them up yesterday, today after draining overnight to 70% when I got full charge I looked and one parallel bank of the 2 in series is 14.2v the other is 13.6v. I was charging to 27.6V so I didn't get another cell/battery overvolt. And it appears I might have gotten one if I went to 28.8v.
I am wondering if 1 or 2 more balancers would help rectify this issue? Or should I drop down to 2 batteries at a time and see which battery is to blame if I have a cell issue.. would take a week to figure it out..

 

[robbob2112]

Do you have an active equalizer/balancer? It should be capable of 10amps. If you don't you need one, it will keep the the voltage of the two batteries within 10mv typically. You should have one per series string if you want to avoid having to take them apart periodically

 

[sunshine_eggo]

Just got done doing that, I charged them 2 days at 12.8v

Do you mean some other number than 12.8V? That won't charge a LFP battery.

and then lowered them a bit then charged at 14.4v for 24 hours.
I hooked them up yesterday, today after draining overnight to 70% when I got full charge I looked and one parallel bank of the 2 in series is 14.2v the other is 13.6v. I was charging to 27.6V so I didn't get another cell/battery overvolt. And it appears I might have gotten one if I went to 28.8v.
I am wondering if 1 or 2 more balancers would help rectify this issue? Or should I drop down to 2 batteries at a time and see which battery is to blame if I have a cell issue.. would take a week to figure it out..

I just realized you have parallel interconnects between the 12V. This should not be the case, and it is not a 2S3P configuration, it is a 3P2S configuration. If you remove the parallel interconnects, you will be able to measure all 6 individual 12V

 

[Shadowhawk]

Do you mean some other number than 12.8V? That won't charge a LFP battery.



I just realized you have parallel interconnects between the 12V. This should not be the case, and it is not a 2S3P configuration, it is a 3P2S configuration. If you remove the parallel interconnects, you will be able to measure all 6 individual 12V

I had removed them to and charged each separately, then paralleled them and charged them to 13.6v Sunday Night, then Tuesday night I ran them to 14.4V and let them sit until yesterday around noon. Each battery was measuring 14.4V and the 4 Bluetooth battery were within .012v on each cell at 14.4V per battery. Originally I had them in 2s3p but I was reading the web and added the interconnects thinking that might help
it didnt...

 

[Shadowhawk]

Do you have an active equalizer/balancer? It should be capable of 10amps. If you don't you need one, it will keep the the voltage of the two batteries within 10mv typically. You should have one per series string if you want to avoid having to take them apart periodically

I have a single Ecoworthy 24v balancer- I'll have to check the amp rating, and I am thinking I need 2 more...
-edit- ecoworthy balancer is 10a

 

[sunshine_eggo]

I had removed them to and charged each separately, then paralleled them and charged them to 13.6v Sunday Night, then Tuesday night I ran them to 14.4V and let them sit until yesterday around noon. Each battery was measuring 14.4V and the 4 Bluetooth battery were within .012v on each cell at 14.4V per battery. Originally I had them in 2s3p but I was reading the web and added the interconnects thinking that might help
it didnt...

Yeah. It usually doesn't, and it removes the ability to assess the individual 12V.

I have a single Ecoworthy 24v balancer- I'll have to check the amp rating, and I am thinking I need 2 more...

You will need one per string.

 

[Shadowhawk]

Yeah. It usually doesn't, and it removes the ability to assess the individual 12V.



You will need one per string.

I'll get 2 more ordered then. Its odd how when I had 2s2p a single balancer worked and everything was great. So what would be the best way to wire this up with 3 balancers? Remove the interconnects but I don't know how to wire that in, Or keep the interconnects and just strait across each series. Like this picture edited

 

[Cmiller]

For what it's worth for others reading this thread now or later, this is why I wouldn't recommend ever using a series connection with Lithium batteries. In general, get batteries that are the voltage that your bank will be, then run those in parallel.

-Edit to clarify: a 12, 24 or 48V battery unit will typically have at least passive cell balancing internally. Even if one unit goes off the rails, the other units in parallel will function fine. Whereas when using a series connection, one goofy battery will effect all others in series with it, and also potentially the whole bank when there are interconnect links yet.-

To OP: I feel like 12/24V balancers tend to not always be too dependable. To be fair, I haven't worked much with them, but from my own limited experience with them they seem to be a bit hit-or-miss on working right and/or keeping up. You could try adding another one. However, I would second what @sunshine_eggo said about removing the interconnects! Do that before anything else, as that potentially gives you the ability to trace the issue to a single battery!

Start with all 6 fully charged to 14.4V, then reconnect the whole bank WITHOUT the interconnect cables, then discharge and see if one series set of 2 batteries goes catty-wompus while the others stay balanced.

I would guess there is a fair chance of a single battery being the whole culprit.

 

[Shadowhawk]

For what it's worth for others reading this thread now or later, this is why I wouldn't recommend ever using a series connection with Lithium batteries. In general, get batteries that are the voltage that your bank will be, then run those in parallel.

To OP: I feel like 12/24V balancers tend to not always be too dependable. To be fair, I haven't worked much with them, but from my own limited experience with them they seem to be a bit hit-or-miss on working right and/or keeping up. You could try adding another one. However, I would second what @sunshine_eggo said about removing the interconnects! Do that before anything else, as that potentially gives you the ability to trace the issue to a single battery!

Start with all 6 fully charged to 14.4V, then reconnect the whole bank WITHOUT the interconnect cables, then discharge and see if one series set of 2 batteries goes catty-wompus while the others stay balanced.

I would guess there is a fair chance of a single battery being the whole culprit.

While discharging the batteries stay spot on within .012V per cell in each battery. It wasn't until I started charging that is goes out of whack.

I started with 2 12v battery on a Renogy Rover 12v system, and then you can guess what happened from there. I assume I will upgrade again in the future and those 400ah Litime are looking sexy... But I might just go 48 V and do something big, Time will tell.

 

[sunshine_eggo]

I'll get 2 more ordered then. Its odd how when I had 2s2p a single balancer worked

Did you have 2S2P or 2P2S?

The only way to use a single balancer is via 2P2S with parallel interconnects. If you had separate strings, and you wired the balancer properly, you were only balancing one string.

and everything was great. So what would be the best way to wire this up with 3 balancers? Remove the interconnects but I don't know how to wire that in, Or keep the interconnects and just strait across each series. Like this picture edited

Like this:

 

[Shadowhawk]

Did you have 2S2P or 2P2S?

The only way to use a single balancer is via 2P2S with parallel interconnects. If you had separate strings, and you wired the balancer properly, you were only balancing one string.



Like this:

View attachment 251861

I had the positive on the incoming positive, common between the 2 parallel banks, and negative on outgoing negative. All I know is it was working with 4 battery.. no I didn't have the 2nd interconnect on the positive to negative on the second series. But it was working...

 

[sunshine_eggo]

I had the positive on the incoming positive, common between the 2 parallel banks, and negative on outgoing negative. All I know is it was working with 4 battery.. no I didn't have the 2nd interconnect on the positive to negative on the second series. But it was working...

It sounds like you formed a parallel interconnect with the common wire. If there had been significant imbalance, this wire would not have survived.

 

[Cmiller]

While discharging the batteries stay spot on within .012V per cell in each battery. It wasn't until I started charging that is goes out of whack.

What about voltage difference battery to battery? Be sure to check that with no interconnections. Only 24V negatives connected and 24V positives connected.

Charge all batteries fully (to 14.4V), then connect up for 24V, then watch individual battery voltage on the way down. Perhaps one battery has some less capacity, despite supposedly being the same exact battery.

I started with 2 12v battery on a Renogy Rover 12v system, and then you can guess what happened from there. I assume I will upgrade again in the future and those 400ah Litime are looking sexy... But I might just go 48 V and do something big, Time will tell.

Yep, I know how that works. I'm sure I would have done the same thing! Thankfully I didn't have any battery/solar/inverter until I had been in the industry for 10+ years. That way I had plenty of time to dream about small systems, and once I was ready for my own system, I knew I wanted to go 48V right away.

There is always room for small 12 and 24V systems though! I've been thinking about doing something small for my barn that is 150' away from the house.... I could get the wire and conduit cheap from work..... or I could scrape together some nearly free used stuff... solar panel, battery, inverter, charge controller, etc....... hmmm, which is more fun....??

 

[robbob2112]

What about voltage difference battery to battery? Be sure to check that with no interconnections. Only 24V negatives connected and 24V positives connected.

Charge all batteries fully (to 14.4V), then connect up for 24V, then watch individual battery voltage on the way down. Perhaps one battery has some less capacity, despite supposedly being the same exact battery.

Yep, I know how that works. I'm sure I would have done the same thing! Thankfully I didn't have any battery/solar/inverter until I had been in the industry for 10+ years. That way I had plenty of time to dream about small systems, and once I was ready for my own system, I knew I wanted to go 48V right away.

There is always room for small 12 and 24V systems though! I've been thinking about doing something small for my barn that is 150' away from the house.... I could get the wire and conduit cheap from work..... or I could scrape together some nearly free used stuff... solar panel, battery, inverter, charge controller, etc....... hmmm, which is more fun....??

HAHA - I like to use free/lowcost stuff and tinker it together myself - I have more time than money to tinker