Capacity difference

[dventu]

Upon scavenging a bunch of cells to build a 72v pack. I have a varied of LG and samsung cells. What would be the Mah tolerance between the cells? I was reading at most the should only be a 30 Mah difference.

Of course the cells with similar capacity will be match in parallel. I was curious if a cell is 3000mah can you be paired with 2950 or so. Each cell is being load tested to ensure the actual capacity.

 

[hemo]

Any battery will be dominated by the capacity of the lowest cells, more importantly is battery sag. The IR's need to be very close as does the voltage, test cells and weed out the poor ones. Charge cells first and then weed out any that self discharge. A mix of 2950 & 3000mah cells, the pack will always be a 2950mah capacity pack.
The mixing of cells isn't advised but if you have to do so make sure there is an equal number of each in the P groups, so all P groups might discharge and act similarly.

 

[Hillhater]

You cannot build a pack with dissimilar used cells and expect to simply use it casually without a lot of attention and monitoring.
So, you could throw any mix of cells capacity , chemistry, age, etc...together in a pack and use it successfully,...providing you understand what it is capable of, what its limits are, and you monitor it appropriately..
IE... You have to know your own abilities and limitations.

 

[flat tire]

You can mismatch capacities in parallel by a pretty big amount and get away with it. You are worrying about nothing. But as mentioned you you need to pay attention to the pack health.

 

[DogDipstick]

You guys wanna see some shit?

 

[DogDipstick]

The fight between good and bad.

This battery has a 5s 1p configuration. One cell is very good, and one cell is very bad, along with three average ones.

You can see the ballet. The balancing charger is doing its best to throttle the high and the low at the same time, while keeping the pack voltage under control at the requested charge current. This is what happens. The cycle repeats, amplifies, and the charger hunts to keep balance.

 

[yusufselimkaratas]

The fight between good and bad.

This battery has a 5s 1p configuration. One cell is very good, and one cell is very bad, along with three average ones.

You can see the ballet. The balancing charger is doing its best to throttle the high and the low at the same time, while keeping the pack voltage under control at the requested charge current. This is what happens. The cycle repeats, amplifies, and the charger hunts to keep balance.

Are you doing active balance?

MI 6 cihazımdan Tapatalk kullanılarak gönderildi

 

[dogman dan]

My advice would be to match up cells by both capacity and resistance, then build packs from similar cells.

That way when you charge, the pack can charge without needing extensive balancing, or any, if you discharge them conservatively.

But once charged, you CAN parallel dissimilar packs, discharge, then charge them separately. They still should be same chemistry and voltage, but you can run your weak pack in parallel with the strong.

Even pretty shitty batteries can extend range a lot, and have decent sag, if you parallel enough of them.

 

[DogDipstick]

The fight between good and bad.

This battery has a 5s 1p configuration. One cell is very good, and one cell is very bad, along with three average ones.

You can see the ballet. The balancing charger is doing its best to throttle the high and the low at the same time, while keeping the pack voltage under control at the requested charge current. This is what happens. The cycle repeats, amplifies, and the charger hunts to keep balance.

Are you doing active balance?

MI 6 cihazımdan Tapatalk kullanılarak gönderildi

It is a powerlab, active balancing with 1A max balance current. 4Ah pack. It is a DeWalt pack.

You know, come to thnk of it, it cant be a 5s1p.. It is a 5s2p, I think.

 

[dventu]

Thx. I'll be actively monitoring the pack via bluetooth bms and controlling my outputs carefully. I just found closer matching battery batch. Same brand and rated capacity. I'll be testing 100 cells and keeping the capacity, and IR close.

After each cell is tested it is fully charged then I'll monitor the voltage drop.

Do anyone of you have a recommend mutiple single 18650 tester? I found a 8 cell charger and tester but that is all. I'll be testing batteries the next 2 weeks at that rate.