Replacing cells in a lifepo4 48v 400ah battery

[viccooper]

I have a 7 year old LifePO4 DIY battery that uses CALB 400ah cells. It is managed using an OrionJr BMS which was not setup to do any sort of active balancing. After years of daily cycling I noticed that the capacity was dropping quite a bit due to the cells being out of balance. So I purchased 6 new EG4 LL 100ah batteries and took the CALB battery off-line. Then I tested each cell using a ZKETech EBC-A40L tester, running a full charge, discharge, charge cycle. It took several weeks to run these tests. The results show that one cell, #14 only has 340ah. A few others are around 370. The rest are above 375ah.

My question to this forum is what to do next?
The options I see are:

1. Replace the lower performing cells. I tried to find a few replacement CALB 400ah cells but after an extensive search including Alibaba I can't find them. My understanding is that they are no longer being made and the industry has settled on the smaller form factor 270 to ~320ah cells.
2. Double up 200ah cells. They other option I am wondering if it will work would be to get two 200ah cells and parallel them together to create a 400ah cell. This has obvious problems in that I could no longer monitor each individual cell. Each double 400ah cell would have to be monitored as one cell. But 200ah cells are quite cheap so if they degrade faster in this configuration it doesn't seem like that big of a deal.

Open to other ideas. Since the overall capacity of this battery would still be around 18kWh it seems like it would be worth investing some money to keep it going another few years. I will be adding a new BMS (Suart Pittaway DIYBMS) and a new active balancer to the battery once I get the low cells replaced.

Thanks!

Test results

Cell number	C-CV-1	D-CC	C-CV-2
14​	369.8​	339​	356.3​
10​	374.6​	368.7​	370.8​
5​	371​	370.6​	374​
3​	379.2​	372.5​	375.7​
2​		373​
13​	379.8​	374​	376​
4​	377.7​	374.2​	374.1​
15​	378.6​	375.6​	377.8​
7​		376.3​	377.6​
11​	382.6​	378.7​	380​
6​	383.4​	381.3​	382.1​
12​	385.1​	382.7​	383.1​
16​	389.6​	387.3​
9​	387.4​	388.2​	390.3​
8​	386.5​	390.9​	390.7​
1​	327.1​

Cell product parameters

 

[Partimewages]

Any reason you can't just use the pack at a lower Ah with a new balancer and BMS?
Any pack will only be as good as the lowest cell. Trying to find cells that match your internal resistance probably won't happen.

 

[MattiFin]

Bit experimental but cheapest option: add 60Ah battery in parallei with the weakest cell.

 

[houseofancients]

I have a 7 year old LifePO4 DIY battery that uses CALB 400ah cells. It is managed using an OrionJr BMS which was not setup to do any sort of active balancing. After years of daily cycling I noticed that the capacity was dropping quite a bit due to the cells being out of balance. So I purchased 6 new EG4 LL 100ah batteries and took the CALB battery off-line. Then I tested each cell using a ZKETech EBC-A40L tester, running a full charge, discharge, charge cycle. It took several weeks to run these tests. The results show that one cell, #14 only has 340ah. A few others are around 370. The rest are above 375ah.

My question to this forum is what to do next?
The options I see are:

1. Replace the lower performing cells. I tried to find a few replacement CALB 400ah cells but after an extensive search including Alibaba I can't find them. My understanding is that they are no longer being made and the industry has settled on the smaller form factor 270 to ~320ah cells.
2. Double up 200ah cells. They other option I am wondering if it will work would be to get two 200ah cells and parallel them together to create a 400ah cell. This has obvious problems in that I could no longer monitor each individual cell. Each double 400ah cell would have to be monitored as one cell. But 200ah cells are quite cheap so if they degrade faster in this configuration it doesn't seem like that big of a deal.

Open to other ideas. Since the overall capacity of this battery would still be around 18kWh it seems like it would be worth investing some money to keep it going another few years. I will be adding a new BMS (Suart Pittaway DIYBMS) and a new active balancer to the battery once I get the low cells replaced.

Thanks!

Test results

Cell number	C-CV-1	D-CC	C-CV-2
14​	369.8​	339​	356.3​
10​	374.6​	368.7​	370.8​
5​	371​	370.6​	374​
3​	379.2​	372.5​	375.7​
2​		373​
13​	379.8​	374​	376​
4​	377.7​	374.2​	374.1​
15​	378.6​	375.6​	377.8​
7​		376.3​	377.6​
11​	382.6​	378.7​	380​
6​	383.4​	381.3​	382.1​
12​	385.1​	382.7​	383.1​
16​	389.6​	387.3​
9​	387.4​	388.2​	390.3​
8​	386.5​	390.9​	390.7​
1​	327.1​

Cell product parameters
View attachment 201717

I'd add a needy active balancer, and keep using them.
Possibly replace that one cell, but these cells done look to be at their usable lifespan yet

 

[viccooper]

Thanks for the responses. I think I will start with upgrading the BMS and adding an active balancer and see what happens. Even with one cell limiting the pack to 340ah per cell, I would still get ~17kWh.

 

[Partimewages]

You can get a BMS that has active balance included.

 

[Raul a/3]

GWL in Czech Republic sell winston cells identical to those Calbs.

 

[toms]

I remember seeing a lot of those cells on the market around seven years ago. When I dug a bit deeper they were all coming from cell brokers that were known to deal with factory seconds and refurbished cells.

Fully charge that battery, then subject it to the highest load you can and measure the individual cell voltages while loaded. That will tell you which direction to go. If there is a big voltage difference under load it won’t pay to invest much in keeping the battery going.

 

[zcskywire2]

If you want to replace the old CALB SE400 cells there are still a few manufacturers out there that I belive still make the 400ah plastic cased cells. They are Sinopoly, Thundersky Winston and GBSystem. The hardest part will be sourcing them. Though as stated above GWL distributes the Thundersky cells. I've added links to the manufacturers websites for all of the cells. I would still recommend modern aluminum case cells. They will be more energy dense in wh/l and wh/kg. They will also will likely have better cycle life than the plastic case cells.

http://www.sinopolybattery.com/userfiles/files/SP-400AH.pdf

Thunder Sky Winston Water Based Lithium Yttrium Power Battery-Energy Storage-thundersky-winston.com-

GBS-LFP400Ah-A - Battery Cells - Zhejiang GBS Energy Co., Ltd.

 

[hwy17]

7 years ago, wow. Was there a forum or community doing this stuff back then or did you just pioneer it?