Charging question for 38120 Headway batteries. 4s5p

[Mark_B]

I have a question about amps to charge a 4S5P battery made up of 38120 Headway cells. These are used cells from battery hookup. My first solar experiment.
I'm building this to learn about all this stuff, my first project. I want to use it for camping and whatnot around the house.
So the advert says: "EACH CELL IS RATED AT 200A DISCHARGE AND CAN BE CHARGED AT 80A. "
The question I have is, does a 13.8v 40amp charger seem ok with the battery I am building?
I want to charge via solar, but am also tweaking an HP server power supply to the 13.8v 40 amp output and want to be able to use that to charge as well.

For solar, I am just learning about panels. I am thinking 2 or 3 175W panels. I already ordered a Victron 100/50 controller.
Any advice is greatly appreciated!
Thanks

 

[snoobler]

4S5P of 8Ah cells should be a 40Ah battery.

Assuming the cells meet spec, CC/CV at 13.8V/40A will be fine; however, to get the battery fully charged, current will likely fall off very rapidly at 13.8V, and charging will be complete once the current has dropped to about 2A. This might take a few hours.

 

[Mark_B]

Thanks so much! My batteries and other stuff should arrive this week. I might post to this thread as I work on the build and balancing/charging before putting them together.

 

[Mark_B]

4S5P of 8Ah cells should be a 40Ah battery.

Assuming the cells meet spec, CC/CV at 13.8V/40A will be fine; however, to get the battery fully charged, current will likely fall off very rapidly at 13.8V, and charging will be complete once the current has dropped to about 2A. This might take a few hours.

I am getting my bus bars together today and have my HP power supply built and tweaked. The supply is at 13.8v and 60Amps, not 40 like I originally said. Is that still ok for charging my 4s6p bank? (I decided to go 6p instead of 5).
I have discharged each battery with a discharge tester like the one pictured below, to 2.1v each. I kept a spreadsheet on original voltage, discharge voltage, and resistance levels for each.
My question now, assuming 13.8v 60Amp CC/CV charger is suitable is this: Do I connect the positive to the main positive on the bank, then the main negative of the charger to the P- on my BMS?
I think that is right, I just don't want to blow anything up.
Second question: Will this balance my batteries? These are used LifePo4 cells and not all had matching stats on the discharge test.

I was thinking of charging them up in this 4s6p configuration, then running the discharge tests individually again and see how the numbers look.
I have no idea if they were matched in SOC when I got them.

 

[snoobler]

I should have commented on terminology. 4S5P implies 5X 4S batteries wired in parallel. If the intent is to parallel 5 cells and then string groups of 5 parallel cells in series, 5P4S is correct (or 6P4S).

Again, if the individual cells are rated for 80A, 6 in parallel can handle 6 * 80A = 480A provided the load is perfectly distributed.

BMS goes between battery (-) and loads/chargers.

A good BMS enabled for balancing during charge only and above 3.4V, then it can SLOWLY balance your cells provided they are all healthy. This could take months.

 

[Mark_B]

I plan to series connect 4 cells (12v), then parallel 6 groups of these. So 4s6p is correct? Total battery voltage goal is 12v (13.???v)

I am using copper bus bars. Is there a trick to evenly distributing the charging current other than the BMS?

I have watched so many videos, but there aren't a lot on the 38120 cells specifically, and I am too green to know what else might apply, other than something related to LifePo4 specifically.
Is there a better way to balance these, like charging each one individually, or maybe groups of 4 as an individual set and see how the pan out?
Since they are used batteries I expect there will be differences in each or in the 4 cell groups and I want to try to identify the really bad ones and not include them. I have 4 extra batteries above the 4s6p set, and if I have to, if there are more bad ones I can do 4s5p to get a good set. Hopefully.

Many thanks for your expertise. I'd be lost without your advice.

 

[Ampster]

So 4s6p is correct?

Yes but you would need 6 separate BMSs if I understand you correctly. Sometimes a picture is clearer.
To answer your question about distributing charge current, the trick many use is to parallel first so you only have 4 groups of parallel cells to balance and monitor with one BMS.

 

[Mark_B]

This photo is what I understand to be correct for 4s6p.

I plan to run bars down 6 cells, so 4 groups of 6 parallel cells, then jumper bars to series them together.
So 6 parallel connected batteries connected together in series (4groups of 6). Is that what you mean?

I am having trouble understanding if there is a difference in parallel connecting 6 groups of 4 series connected cells vs the other way, 6 in parallel, then connecting 4 of those together. Isn't that the same thing as far as circuitry?
It seems to me that either way you have 4 series connected groups of 6 parallel cells. ?

My BMS is 4s. Dely

 

[Ampster]

Electrically they are the same. Some will argue that one should make the series connections first as in your second diagram. I don't have an opinion especially with a small pack like that even though my experience with Headways years ago is very respectful since their discharge capacity is huge.
Thanks for the pictures. Both of those are described as 6P4S
EDIT: After looking at your picture more closely I realize it is the same scheme showing the top and the bottom so my comment above needs to be clarified. Because Headways have terminals on top and bottom your picture is the only way to make a 6P4S pack.
I think your question is with regard to a pack described as 4S6P in which six individual 12 volt batteries of
four cells each are paralleled at the 12 volt level. That situation would require six BMSs

 

[snoobler]

Since I don't want to draw it all, here's a representation of 4S2P



Batteries are only paralleled at the end terminals and require a BMS for each battery.

You are pursuing 6P4S.

 

[Mark_B]

OK, I think I got it. So a 6P4S pack will require a 4S BMS, as pictured below?
Also, would it make sense to do a one time balance charge with a 4s (4cell) pack and do that six times to get them balanced and tested to make sure they are good? I would hook up my 4S BMS to the 4 cells, charge them, then probably discharge and charge again to test them out.

If this is the case I can do that. What are the red flags I should be paying attention to so I can find the bad batteries?
High resistance? Too high or too low at full charge? ??
Again, many thanks!

 

[snoobler]

You really need to test all cells for capacity and internal resistance. Otherwise, you can't really be confident that you have good cells.

 

[Mark_B]

You really need to test all cells for capacity and internal resistance. Otherwise, you can't really be confident that you have good cells.

I'm doing my best with my limited understanding to do that.
I figure discharge them all to 2.10v, which I have done. Now I want to charge them up to full roughly, but evenly, and then do another discharge test. That is about the extent of my knowledge of finding bad cells.
My tester will discharge and shut off at a set voltage. It shows amps, AH, Volts, Resistance.
Right now I am trying to figure out how to charge them effectively.

 

[Mark_B]

I hooked up my battGo meter and power supply and have started charging. They show 15% right now.
They ranged from 3.223 to 3.31 at the start. Now they are all 3.232 +/- .001
Not sure what #8 is on the meter. ? :/
It is throwing the total voltage off as you can see.
Any comments, thoughts etc appreciated.

 

[Mark_B]

So I've been charging several batches of 4 batteries as shown in the pics below.
I have them hooked up to my 13.8v 60amp CC/CV charger through the BMS with a battery monitor as well.
Some are definitely different than others in the same 4 battery group.
The ones that show they are charging at a higher voltage and more quickly, are those the ones that are weak or strong in the group?

 

[KC7NOA]

I cant speak to the question of week or strong ... lots of possibilities...

You can modify the HP server power supply to output 14.5v if you need to ... the current regulation needs addressed if used only ... im still looking for a good adjustable CC/CV device