Is my 12v LiFePO4 Battery dead?

[999zip999]

Funny trick about batteries voltage is one thing capacity is different and throwing internal resistance in which causes heat. A mixed bag of tricks.

 

[999zip999]

Of course they were in parallel. You need to separate and charge each 20ah cell to 3.65v. Batteries are as one in parallel. So if you charge those 4 and let set you might find one or two. May be weak.

 

[joelshort]

The balancers arrived today, and I have the full pack put together. The BMS was hooked up just like in the picture above, and each block has a balancer connected to it. I put it on the 10A charger and it's charging as we speak.

So just how much heat is acceptable for those balancers? They are quite HOT to the touch. All 4 balancers are hot. Should I be concerned?

I'm constructing the pack so that the balancers are surrounded by air,but only by about 1/4 inch.

 

[999zip999]

Give a hand is a fair judgement. It's good to get warm is good run if it is hot it's not good at all giving you a high internal resistance. Most solder melts at 360F. 212F boils wster so 140F is getting a little warm. If it burns your fingers is hot.

 

[flippy]

If all of them are hot then the battery is full and/or the charger voltage is too high so you are just burning up power directly from the charger to the balance boards.

 

[joelshort]

If all of them are hot then the battery is full and/or the charger voltage is too high so you are just burning up power directly from the charger to the balance boards.

The charger puts out 14.6v. If I disconnect the balance board from any one block then the charger shuts down when that block reaches 3.78v

Is there any way to cut off the charger when the battery is full with the balance board connected?

The resting voltage of the 4 blocks with balancers connected appears to be 3.58v, 3.52v, 3.52v, 3.48v. I thought the point of the balance boards was to keep the blocks at the same voltage?

 

[flippy]

Then the charger does not put out 14.6 but something more.

 

[joelshort]

Then the charger does not put out 14.6 but something more.

The output of the charger measures 14.58v as measured with a multimeter.

I'm currently doing a load test of the battery. I'm pulling about 5A and I've noticed that under load each cell block is measuring 3.28v. We'll see how long the battery lasts.

 

[flippy]

if a block reaches 3.78 then something is fucky. is that with the active balancing devices?

 

[joelshort]

if a block reaches 3.78 then something is fucky. is that with the active balancing devices?

No, I did something kind of stupid I think. I disconnected the balancer on just that one block of cells and left the other balancers on. Then I hooked up the charger. That block went up to 3.78 then the BMS or the charger cut off the charge.

With all the balancers connected to the blocks the charge on each block never went above 3.64v (some were lower) but the problem is that the charger never shut off and the balancers got really, really hot.

The good news is that I did a load test. I was pulling 5-6 amps for 11 hours before the battery went down to 12.8v, at which point I disconnected the load. After resting overnight the charge on each block reads 3.27v. So that should be about 80% discharged which is what I would expect and I'm thrilled that the battery has recovered that capacity.

Now I'm going to remove the balancers and try to charge it and see how that one low block behaves. When I started the load test, that block read 3.48v while the other blocks read 3.53v As soon as I put the load on all 4 blocks read 3.28v (with the balancers on).

I don't feel like I can leave the balancers on if the charger won't shut off and the balancers get super hot. Hopefully now that the blocks are better balanced the BMS will be able to keep up with the balancing part.

 

[jonyjoe303]

On my lifepo4, it needs the active balancers all the time, I disconnected them before and the unbalance condition returns. The active balancers I use never get hot, but in your situation, a good idea would be to put a fan blowing on the balancers that turns on whenever your charging. They only heat up when charging.
They seem to be doing the job, the heat won't damage the balancers, but will heat up the area they are in.

 

[999zip999]

I have a 5yr old pack of cells from 2009. I balanced yesterday after 17ah out of a 18ah pack @ 80amps 1288 cycles. So balance craghed and still 3.49v - 3.51v oh A123 cells. So heat is a warring sign. Lifepo4 can take 3.90v Not recommended and we'll go down to (3.7. Sorry )lower fairly fast if disconnected. You can always add a 12v 30ah battery. And watch the dodgy cells. Or add one lifepo4 cell to the weak . 10 or 20 ah. Then the low cell has more capacity. Or add one to the low group. I think what I meant 3.4v 10ah or ? Sorry Im being eaten by gnats

 

[joelshort]

I've got good news and I think the pack is sufficiently recovered. After discharging the battery approximately 55AH, I removed the balancers and charged the battery with just the BMS connected. Then rested the battery overnight. The voltages read 3.53, 3.53, 3.52, 3.48. These voltages are pretty much exactly the same as with the balancers connected.

I'm going to do one more load test with the balancers removed and see how the battery cell blocks behave, but I believe that the BMS is capable of balancing sufficiently and I won't need to leave the extra balancers on.

 

[flippy]

very nice.

always good to see good stuff happen.

 

[joelshort]

very nice.

always good to see good stuff happen.

Thanks SO MUCH for all your advice (and others in the thread too). I certainly appreciate it.