Correct Charge Current for Lifepo4 Cell battery banks

[8e7Design]

Good afternoon all,

I'm after a bit of advice on calculating the correct charge voltage and current for my new build Lifepo4 Battery. I've read too many differing bits of information and I am now really confused!

I have a load of K2 Energy 26650 cells (3.7ah - 11.84wh- data sheet attached), 120 of them in fact. I'm intending on creating four parallel banks of 30 cells to hopefully give me a 111ah 12v battery (3.7ah x 30) x 4 in series)

The recommended charge current for each individual cell is 1.8A (Max operating charge current of 3.7A) and the recommended charge voltage cutoff is 3.65v (Max of 4.1)

So the voltages are simple (I think), and I should set the controller to charge each cell bank to 3.65v before connecting the four cell banks in series to create the '12v' battery. After that (and the battery having been discharged) I change the charge controller charge to 14.6v... Someone please confirm if that is correct? : )

It's the charge current I am confused by... I presume the charge current gets shared by each of the cells in the parallel cell bank? So I should charge each cell bank of 30 cells at 54A (max of 111A) and 3.65v? Am I correct on that?

What about when the battery is then put together and then discharged? Do I carry on charging at 54A and 14.6v??

I would really appreciate if someone could help me out with confirming the correct levels in order for me not to damage the cells & battery! : ) I've spent a bit of money on this now and don't want to damage anything.

PS. I have a 120A BMS on order to manage the battery once built.

Thanks for reading!

Charlie

 

[John Frum]

Typically lifepo4 batteries are recommended to be charged at 0.2c=22.2 amps.
The spec sheet says you can go as high as 0.5c=55.5 amps.

 

[Forbisher]

I have a load of K2 Energy 26650 cells (3.7ah - 11.84wh- data sheet attached),
120 of them in fact.
four parallel banks of 30 cells to hopefully give me a 111ah 12v battery (3.7ah x 30) x 4 in series)

That is the same lay out of a 100Ah Battle Born battery. 120 cells in 4 x 30 cell groups.

 

[MisterSandals]

and I should set the controller to charge each cell bank to 3.65v before connecting the four cell banks in series

This would be a good way to top balance the cell banks. Make sure that after top balancing that they self discharge to the same level in roughly the same amount of time. If this happens, then your cell banks are likely well matched. If not, you may need to figure out which individual cells are outliers.

After top balancing, "my preference and beliefs" are that since most of the voltage charts (yea, i know, a terrible indicator) show 3.6v and above to be 100% charge, that charging above that is unnecessary and maybe taxing on the battery longevity.
I charge to about 3.45v (where my SCC cuts out is 13.80v) - I think that everything over that is unnecessary.

Try different charge scenarios and see how your batteries perform. Please share what you learn as part of the collective.

 

[8e7Design]

That is the same lay out of a 100Ah Battle Born battery. 120 cells in 4 x 30 cell groups.

That's handy to know, hoping it performs somewhere in that region then! : )

Cheers!

 

[8e7Design]

This would be a good way to top balance the cell banks. Make sure that after top balancing that they self discharge to the same level in roughly the same amount of time. If this happens, then your cell banks are likely well matched. If not, you may need to figure out which individual cells are outliers.

After top balancing, "my preference and beliefs" are that since most of the voltage charts (yea, i know, a terrible indicator) show 3.6v and above to be 100% charge, that charging above that is unnecessary and maybe taxing on the battery longevity.
I charge to about 3.45v (where my SCC cuts out is 13.80v) - I think that everything over that is unnecessary.

Try different charge scenarios and see how your batteries perform. Please share what you learn as part of the collective.

Thanks, I will do. Thanks for the advice guys!

Charlie