Compression, Balancing, Reconfigure the pack

Njord

Solar Enthusiast
Joined
Mar 14, 2021
Messages
19
I've been reading around on the forum about compressing LiFePo4 batteries but my question isn't about how to compress the batteries specifically.

When you're top balancing the cells (all in parallel, 3.65v) and the charge is complete, one would want to disassemble the compression, rearrange the cells to a more useful voltage (~12v) for discharging or using.

I came across a video that I'm hoping was being over the top, but it went on to say that once the cells are above 3.4v, the compression should not be removed as the cells could start to swell.

So my question, Once the cells are top balanced (3.65v), how does everyone go about reconfiguring their pack to their nominal voltage (12/24/etc..).
Do you, after top balancing;
  • dissasemble the compression, and rearrange as the cells wont swell in the 5 mins it takes to reconfigure
  • Arrange the pack to its final configuration and use wire/jumpers to parralell. Once charged its just swapping in bus bars
  • No compression because its something that wont happen until the batteries age and 1-2 cycles is fine.
Thanks!
 

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,342
A third option would be to arrange the cells as they will be in their final configuration ..... but make up wires that will electrically be parallel.

A fourth option would be to arrange and wire them in series and then use a combination things to manually balance the cells once you get them charged to the knee. This might involve manually bleeding off the high cells with a resistor .... or charging the low cells with the power supply connected to a single cell.

But .... I don't think you will have any problems using the approach you outlined either. You are probably ahead of most people by compressing the cells while you have them in parallel.

My cells were well enough balanced that I never did have to put them in parallel to get them balanced.
 
Last edited:

jwelter99

Solar Addict
Joined
Dec 6, 2020
Messages
552
I like to:

Parallel balance (won't get into the topic of how as many opinions/threads on that)
Discharge pack to about 80% of capacity
Parallel balance again to ensure cells really are balanced/stable
Discharge pack about 50% of capacity
Disassemble and assemble into the final topology

I do not like to assemble the pack if below or above 50% SOC

If you have swollen cells you need to solve that before assembly. It can not be "compressed" away. You need to take the cells down to 10%; hope the swelling goes away, compresse, and charge back up.

Very bad things happen if you try to compress significantly swollen cells.
 

Stepandwolf

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Nov 14, 2020
Messages
635
I didn't get out my micrometer, but I don't think my Lishen or EVE cells swelled when top balancing. I read that I should have compressed them, but didn't.
 

Stepandwolf

Solar Addict
Joined
Nov 14, 2020
Messages
635
What voltage and charge rate?
I only have a 10A PS and when connected to 8 batteries, that is pretty slow. I have also used it on individual cells when I was load testing them. Always 3.65V and I have overrun to 3.71 and 3.73.
 

self_sufficient_25

Solar Enthusiast
Joined
Nov 10, 2020
Messages
48
Cool beans....I can't do 16 at a time since I am still load testing the first eight. I am OK charging the second eight at once which I am doing now.
I actually typically charge them up with a BMS first
And than do a top balance. Because without my little 10 amp variable power supply it would take days😊
 
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