Top balancing tail current? How low?

[Jet]

I'm charging sets of 4 100aH cells fortune/frey in parallel (3.2V 400aH cell packs) to capacity test them. They started out at around %65 SOC. I am using a 10 amp bench charger. Using the cheap leads that came with the power supply I can only get 4.6 amps. Even after adding ring terminals on the battey cell end. And will proses video. He says the current drops near zero. What exactly does that mean? I assume the current will be higher depending on the number of cells in parallel.

The tail current for the cells is 0.05C or 5 amps. Multiplied by four cells that 20 amps. The Bench charger'd constant current limit is 10 amps and I'm getting less then half of that. I did buy some heavier duty banana connectors and will be making some 10 awg cables.

 

[SeaGal]

@FilterGuy's top balancing guide may be helpful - see page 5

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

 

[chrisski]

The 10 AWG cable should bring it up to 10 amps.

I went from from 3.6 amps with the cables that came with the BMS to 10 amps when I made my own 10 AWG cables.
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For the tail current to stop at, I stopped at less than .1 amp.

Yes you can reach 0 amps but IME, limited compared to @FilterGuy , I found that there’s a point where waiting is not worth it. I had my 25 ah Top Brand cells tail current taper off so slowly at the end of the “knee” the amount of energy going into the battery was not worth eating for 0.

I had waited for a couple hours and the cells were still taking less than .1 amp. For me to get it to 0, I went to sleep and woke up and it was 0.

 

[RCinFLA]

Additional series resistance from cheap cable leads will greatly increase the charge taper current time.

 

[Jet]

The 10 AWG cable should bring it up to 10 amps.

I went from from 3.6 amps with the cables that came with the BMS to 10 amps when I made my own 10 AWG cables.
=============
For the tail current to stop at, I stopped at less than .1 amp.

Yes you can reach 0 amps but IME, limited compared to @FilterGuy , I found that there’s a point where waiting is not worth it. I had my 25 ah Top Brand cells tail current taper off so slowly at the end of the “knee” the amount of energy going into the battery was not worth eating for 0.

I had waited for a couple hours and the cells were still taking less than .1 amp. For me to get it to 0, I went to sleep and woke up and it was 0.

Thanks for your help! For some reason I wasn't getting notifications on the form even when I clicked on the notification icon. Not that anyone has to answer my question but I appreciate it.

Will Prose said almost zero and other places talked about tail current. I wanted to make sure I didn't ruin the cells. I bought them 2 years and they were stored in a warm shed one summer. They were still within 0.002 Amps of each other before charging 3.289 - 3.291.

 

[Jet]

Additional series resistance from cheap cable leads will greatly increase the charge taper current time.

Even with the full 10 amps it'll take a week to charge all 16 cells. I do have a multi-plus but I don't want to go to all the work of setting the BMS up and then taking it all apart to rearranging the cells again to top balance all the cells with each other. I'm top balancing sets of fourth for capacity test. They've been sitting for 2 years. If they're still good I might go with the company again when and if I do solar for the whole house. Thanks for your help.

 

[Jet]

The 10 AWG cable should bring it up to 10 amps.

I went from from 3.6 amps with the cables that came with the BMS to 10 amps when I made my own 10 AWG cables.
=============
For the tail current to stop at, I stopped at less than .1 amp.

Yes you can reach 0 amps but IME, limited compared to @FilterGuy , I found that there’s a point where waiting is not worth it. I had my 25 ah Top Brand cells tail current taper off so slowly at the end of the “knee” the amount of energy going into the battery was not worth eating for 0.

I had waited for a couple hours and the cells were still taking less than .1 amp. For me to get it to 0, I went to sleep and woke up and it was 0.

Thanks for your help. The way the charger is designed using ring terminals on it wouldn't work well. It's just bigger then a #10. I tried drilling the ring terminal but it always got very bent up or broke by the time I got it there. Also tried filing it with similar results. I don't have a drill press. There is a threaded post if you call it but it tapers small at the bottom so any ring terminal would be really loose. There isn't much of a contact patch at the base of it. I took the charger to home Depot and couldn't find a nut that fit it either. I bought some big banana connectors online that is set 8-12 awg wire.

 

[Jet]

@FilterGuy's top balancing guide may be helpful - see page 5

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

Thanks for the reply. I had read that when I was first getting started it is very helpful. It says to change the cells at 3.625. Other places say 3.65 as does the seller of the cells I'm using. I'll turn the voltage down to 3.63 (my charger doesn't have 3 decimals) if I have to leave them unattended for a short time. Thanks for your help.