Top Balancing - this will take ages?!? Did I miss something?

[cmpct_cmpr]

Hello all,

I'm starting building my first LiFePo4 battery from 4 prismatic cells.



Having watched Will's video on top-balancing, I connected my cells in parallel and hooked them to my power adapter at 3.65 V.
Within 3 hours, it went from 3.553 down to 3.392 A, but it has to go down to 0, won't this take ages?
Did I miss something? Did I do sth wrong? How can I speed up the process?

 

[Jordi]

At 3,5 A (to round it up) and If charging voltage matches the battery full charge voltage, means you are providing 3,5 Ah per hour. If your cells have 120 Ah each (example) and are connected in parallel then total battery capacity is 120x4 = 480 Ah. Then 480/3,5 = 137 hours (at least!!) required to full charge. If current goes down over this process, then expect some extra hours.

 

[Deleted member 9967]

This is why Will uses a heat gun to lower his cells. And even then it can take many hours.
Me, I just used them like I normally would and when they got close to 2.7 or 2.8 per cell I called it good and then boxed them and then charged them up to 3.65 by charging first in series to 3.55 and then in parallel to 3.65.
Then I let them sit for 24 hours and they went down to 3.4ish.
After this they were top balanced and ready for real and proper use.

Hope this helps.

Also I have 8 - 280 Ah cells and yes it can take a while.
Took me a week to use them up on my mobility scooter. But it was fun doing it.

 

[Bob142]

How can I speed up the process?

Download this top balancing tutorial from the forum Resources section and follow the instructions exactly. Quick summary is that you'll assemble your pack in series and connect the BMS, then you charge the whole pack to 14.6V allowing the BMS to cut off charging when a cell hits 3.65V. Then you disassemble and go back to exactly how you have it now to finish off the balancing. During the series portion of the charging you'll be going 4x faster than in parallel so this method speeds it up considerably.

Alternatively you can buy a much bigger power supply and keep doing a parallel top balance as you are now.

Edit: a bigger power supply would be helpful either way you try to balance. I've been using this 15V 40A power supply. Top balancing 4 280Ah cells has taken about 7 hours each time I did it following the tutorial and using that power supply.

 

[Bob B]

Make sure you adjust the voltage BEFORE you connect the leads to the batteries .... Otherwise, as the cells approach full charge, the voltage will increase and ruin your cells.

Also not a bad idea or replace the cheap alligator clips that come with those power supplies with something better.

 

[cmpct_cmpr]

Thank you everyone! It took me some time to get back to the cells. Followed the tutorial, built them up serially with bms and charged with 14.6 V, then paralleled the cells and continued at 3.65 V. Amperage went down to about 0.020 after a full day. Disconnected to power supply after some more hours and let it sit another few hours. The paralleled pack was at 3.626 V and wouldn't seem to go beyond, I guess I let it be like this.

Thank you all again! And I'll definitely get better clips!