Is my 12v LiFePO4 Battery dead?

[joelshort]

No, it is very important you finish out at 3.65v.

Then disconnect the block and leave them for 24h.
Then measure the voltage on each block. If they are identical you are good.

Got it. Thanks.

What happens if after 24hrs the blocks are different?

 

[999zip999]

Sorry earlier I wrote 13.3v I meant 3.3v normal.. But 80ah is big and never believe what printted on side of charger and always test pos and neg.

 

[joelshort]

You weren't kidding. The charging went really fast once it got to 3.50v.

I charged until it read 3.65v then disconnected the 4 blocks from each other. After about 10min I check the voltage and they read:
3.52v
3.58v
3.6v
3.61v

The 3.52v block is also the one that had been discharged the most when this started. I'll wait 24hrs and report back.

 

[999zip999]

It depends on rate of self discharge ? It could be one out of four of the block or two and a another block could havre all good . then one have one bad. As yoy also have 16 20ah cells as bluiding blocks for a 12v battery. A self discharging cell is limited for use. You could make 4 12v 20ah batteries. Just saying.
Good job.

 

[999zip999]

So 3.65v each bank ok. If all stayed above 3.5v New battery if all above 3.45v after a few days golden. If if let us knonw . 3.45v is a great number as could be. May need more probes or multiple probes if you're ready at one time like a four-way probe we'll talk about that later first just worry about what you got.

 

[joelshort]

Just an update after 14hrs. The voltages are:
3.32v
3.48v
3.55v
3.59v

So the trend isn't good. The 3.59v and 3.55v packs have remained quite steady. The 3.32v and 3.48v fairly quickly reached those voltages but have remained steady for probably 8hrs now.

I'll report back after the full 24hrs again.

 

[joelshort]

No, it is very important you finish out at 3.65v.

Then disconnect the block and leave them for 24h.
Then measure the voltage on each block. If they are identical you are good.

I'm not sure that I understood this correctly. After the charge of the whole block reached 3.65v, did you mean that I should simply remove the charger and leave it as one big block for 24hrs, or did you mean that I should disconnect the 4 blocks from each other and leave each one separate for 24hrs?

 

[999zip999]

They are fine for now as the are connected we can separate and break down the block for the low voltage later 3.48 is not a game breaker. You may just have one bad cell in one block

 

[flippy]

No, it is very important you finish out at 3.65v.

Then disconnect the block and leave them for 24h.
Then measure the voltage on each block. If they are identical you are good.

I'm not sure that I understood this correctly. After the charge of the whole block reached 3.65v, did you mean that I should simply remove the charger and leave it as one big block for 24hrs, or did you mean that I should disconnect the 4 blocks from each other and leave each one separate for 24hrs?

No, remove all 4 blocks from each other and let them be for a day.

If the voltage lowers too much you have bad cells.
Then you can crack the blocks for their individual cells and charge them again, then disconnect the individual cells and see which ones keep their voltage best.

 

[joelshort]

It's been 21hrs now. The voltages haven't moved in the last 15hrs (3.32, 3.48, 3.55, 3.59).
So what constitutes a voltage that is too low and is suspect?

 

[999zip999]

In the 3.32v block there can be just one or two bad cells. The rest look fine. My lifepo4 battery charges to 3.5v andas soon as I go around the block goes to 3.4v or 3.38v and stays there for miles. Very flat dis charge after that.

 

[flippy]

It's been 21hrs now. The voltages haven't moved in the last 15hrs (3.32, 3.48, 3.55, 3.59).
So what constitutes a voltage that is too low and is suspect?

the .32 is way too low. the .48 is borderline.

the 2 other blocks are fine.

recharge the 2 low blocks to 3.65 again and then take out ALL the connections so you end up with a bunch of separate cells. see if there is only a few bad ones or whole blocks.

 

[joelshort]

It's been 21hrs now. The voltages haven't moved in the last 15hrs (3.32, 3.48, 3.55, 3.59).
So what constitutes a voltage that is too low and is suspect?

the .32 is way too low. the .48 is borderline.

the 2 other blocks are fine.

recharge the 2 low blocks to 3.65 again and then take out ALL the connections so you end up with a bunch of separate cells. see if there is only a few bad ones or whole blocks.

I did as you said and charged the two low blocks again and separated the cells.

After 20hrs, the cells in the block that read 3.32v before now read 3.3, 3.3, 3.4, 3.4. So that whole block appears to be bad.

But the surprising thing is that the cells in the block that originally read 3.48v, after 20hrs, ALL read 3.55v. So I think I'm good there.

 

[flippy]

i think the cells were not saturated enough. they need to be kept floating longer at 3.65V in order to recoup more capacity.

 

[joelshort]

i think the cells were not saturated enough. they need to be kept floating longer at 3.65V in order to recoup more capacity.

So I need to find a way to maintain 3.65v. How long should I float charge?

 

[flippy]

i think the cells were not saturated enough. they need to be kept floating longer at 3.65V in order to recoup more capacity.

So I need to find a way to maintain 3.65v. How long should I float charge?

6~8 hours or until it wont accept any more charge (less then .5A for a block.)

 

[joelshort]

6~8 hours or until it wont accept any more charge (less then .5A for a block.)

So I'm not very confident that this block will recover. I started the float charge about 2hrs ago. I'm not sure that I'm reading everything correctly, but at first the power supply was reading a 3A draw while charging but it quickly went down to about 0.3A draw. After the charge reached 3.65v the draw went down to 0.1A. I'm going to leave the charger on for 8hrs and see what happens.

Assuming that this cell block is bad, will I be able to simply replace those cells and add them to the existing/good cells and get my 12v battery back? And can anyone recommend a good supplier (China or otherwise) for low cost but good cells?

 

[999zip999]

How old is this battery ?

 

[joelshort]

6 years old. Used 5-6 times per year.

 

[jonyjoe303]

You can use active balancers and just keep using it. My 12 volt lifepo4 also has one cell that has always been low, when charging it reads 3.40 volts while the other 3 read 3.60 volts. I wasn't going to rebuild the pack with new cells. Last year I bought some active balancers, and the battery has stayed in perfect balance ever since, I use it every day.
Cost is about 100 dollars for a 4s active balancer module. You just connect them to the 4s balance connectors. They are always balancing in the background. They transfer amps from the high cell to the low cells, and can handle up to 10 amps per cell, you can fast charge your battery pack.

electriccarpartscompany sells them. I think it will be cheaper then rebuilding your pack. Even though your battery pack is 6 years old, it looks like it still got plenty of life left in it.

 

[joelshort]

You can use active balancers and just keep using it. My 12 volt lifepo4 also has one cell that has always been low, when charging it reads 3.40 volts while the other 3 read 3.60 volts. I wasn't going to rebuild the pack with new cells. Last year I bought some active balancers, and the battery has stayed in perfect balance ever since, I use it every day.
Cost is about 100 dollars for a 4s active balancer module. You just connect them to the 4s balance connectors. They are always balancing in the background. They transfer amps from the high cell to the low cells, and can handle up to 10 amps per cell, you can fast charge your battery pack.

electriccarpartscompany sells them. I think it will be cheaper then rebuilding your pack. Even though your battery pack is 6 years old, it looks like it still got plenty of life left in it.
active balancers.jpg

Interesting. So what is the difference between this active balancer and the battery BMS? I thought one purpose of the BMS was to balance the cells.

 

[joelshort]

i think the cells were not saturated enough. they need to be kept floating longer at 3.65V in order to recoup more capacity.

So I need to find a way to maintain 3.65v. How long should I float charge?

6~8 hours or until it wont accept any more charge (less then .5A for a block.)

I left the block on the charger for about 8hrs and let it rest overnight. After resting for perhaps 12hrs the block read 3.44v. So I left it on the charger for another 8hrs. The block has now rested for 8hrs and it reads 3.49v I'll let it rest another 12hrs and see where it's at then.

 

[jonyjoe303]

active balancer are always balancing whether charging or discharging, it keeps battery from drifting out of balance and the balancing amps per cell is up to 10 amps peak (6 amps constant). This will keep up when you charging at high amps(fast charging). I can charge my battery at 15 amps until its almost to 100 percent.
The battery BMS will only start to balance when the battery voltage reaches 3.60 volts, then it bleeds the amps until the other cells catch up.
And most only balance at 60 ma, which is nothing. If the battery is out of balance you will get no balancing done because the BMS will always shutoff charging when the high cell reaches the limit. If you charge at more then 1 amp, it will usually not get a full charge, 60 ma wont be able to bleed it off fast enough.
Some of those lifepo4 batteries have some balance modules on each cell, it looks like this picture, these can balance at up to 1.4 amps. A 4s battery will have 4 of these modules, 1 on each cell. Even these will only start to balance when the cell voltage reaches 3.60 volts, if you charge at less then 4 amps, they will keep up. These cost about 7 dollars each.

 

[joelshort]

i think the cells were not saturated enough. they need to be kept floating longer at 3.65V in order to recoup more capacity.

OK, to recap what I have done:
I took the block that originally read 3.32v and I float charged it at 3.65v for about 16hrs. After resting for 20hrs it now reads 3.44v. Should I keep float charging to see if it will saturate more, or is that pointless?

And I still would like to know if I can simply replace those bad cells/block and add it to my existing cells?

 

[flippy]

i think the cells were not saturated enough. they need to be kept floating longer at 3.65V in order to recoup more capacity.

OK, to recap what I have done:
I took the block that originally read 3.32v and I float charged it at 3.65v for about 16hrs. After resting for 20hrs it now reads 3.44v. Should I keep float charging to see if it will saturate more, or is that pointless?

And I still would like to know if I can simply replace those bad cells/block and add it to my existing cells?

yes you should and no you cant because then you are putting brand new cells next to older cells so the problem shifts again to the older cells.

i would order a couple balance boards and put those on each bock to keep them in check.