280Ah cell top balancing

atti

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I purchased some (not so good quality) cells from Aliexpress and I am struggling to top-balance them due to their large capacity (280Ah, allegedly).
I wish I had something like 50-100A charger at 3.2v. Can I use buck converter charger like this and make it charge faster? Any experience of using these sort of products?

I used imax b6 charger after fully charging the cells in the inverter, I first charged them to max capacity in batch of 4 and then connected them in parallel, but leaving B6 charger at max current (6A) for few days didn't do much, cells voltage didn't go past 3.35v after many many hours. How can be possibly top balance them all to 3.6v?
 
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How many cells do you have?
What nominal voltage will your battery be?
Do you have a charge source for the nominal voltage?
 

atti

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How many cells do you have?
What nominal voltage will your battery be?
Do you have a charge source for the nominal voltage?
16s, 48v pack, 51.2v charged state (AFAIR), Seplos 100A 16S BMS and it is installed with Sofar Solar ME3000SP.
 

S Davis

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A set of four EVE 280 cells takes me 72-76 hours with a 10 amp power supply. You have to remember the cells are 280ah @ 3.2 volts so if they come half charged you are stil looking at 140ah per cell to charge. You need to chill, if you aren’t careful you can ruin your cells in a flash. Unless I was standing in front of them every second I would not use higher voltage.
 

Hedges

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I used imax b6 charger after fully charging the cells in the inverter, I first charged them to max capacity in batch of 4 and then connected them in parallel, but leaving B6 charger at max current (6A) for few days didn't do much, cells voltage didn't go past 3.35v after many many hours.

"after fully charging the cells in the inverter, I first charged them to max capacity in batch of 4"

That is the way to speed things up (with BMS monitoring each cell and protecting them by stopping charging of battery). But I guess if one was received 90% and one was 30%, you'd be left with 60% to charge slowly with 3.6V low current charger.

If you have many and can batch them in groups of say four cells of similar SoC, you could series charge (with BMS) as a 12V battery using (12V) inverter. After multiple sets have been series charged to similar SoC, then they can be paralleled. Less remaining charge Ah needed.
 
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16s, 48v pack, 51.2v charged state (AFAIR), Seplos 100A 16S BMS and it is installed with Sofar Solar ME3000SP.
Configure the cells into a 16s battery complete with bms.
Charge the battery to 54.4 volts(3.4 volts per cell) with a charge current of ~28 amps.
If the bms trips report back with the cell voltages after they settle for 2 hours.
If they don't trip increment the charge voltage to by 100 milli-volts and repeat until you get to 56.8 volts.
Depending on how far out of whack the cells are and at what voltage the bms trips we will decide the next move.
 
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Ampster

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You have to remember the cells are 280ah @ 3.2 volts so if they come half charged you are stil looking at 140ah per cell to charge. You need to chill, if you aren’t careful you can ruin your cells in a flash. Unless I was standing in front of them every second I would not use higher voltage.
Just to be clear, 3.2 is the nominal voltage. I used an output voltage on my power supply of 3.7 volts and charted the Amperage. When the current started tapering I shut off the power supply. The cells never got past 3.58 volts.
 

atti

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I have spent good amount of money to buy these cells and since last 2 months they remain unused due to this balancing problem. It is difficult to take it off and put it on the bench to balance, I am wondering if buying a 5A balancer is a better choice at this point instead of faffing with tiny cells and waiting for ages for the top balancing. What do you suggest?
 

atti

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Must add that I would have lost more money as the system is not in practical use, so any cornering cutting seems pointless to me.
 

Hedges

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The most important thing (after human safety) is to not overcharge any cells.
A power supply set no higher than 3.65V, or a BMS able to terminate charging of a battery, is necessary for that.

If you make a list of all cells, give a number to each and list resting voltage,
plus list of available equipment (power supply voltage/current capability, BMS model and number of cells supported, charging sources),
one of us might be able to recommend how to get all fully charged in less time.
(I'm thinking of small groups of cells of similar SoC being series charged until BMS disconnects, then parallel charged.)

Perhaps as you suggest a higher current balancer will bring them more in line over time, while allowing use.
But people here have had some issues with active balancers, either balancing when they didn't want them to or vice versa, can't remember exactly.

If already installed wired series (or series/parallel, or parallel/series), topping off individual low cells with power supply may also be an option.
 
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I have spent good amount of money to buy these cells and since last 2 months they remain unused due to this balancing problem. It is difficult to take it off and put it on the bench to balance, I am wondering if buying a 5A balancer is a better choice at this point instead of faffing with tiny cells and waiting for ages for the top balancing. What do you suggest?
I've already told you how to preceed.
Depending on the outcome of the process I outlined an active balancer may be in your future.
 

Ampster

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What do you suggest?
At this point I would not waste the money on a 5 Amp active balancer. The 2 Amp version I have works fine on a 3P16S pack. Once balanced it should not take much current to keep it balanced. If you do that be sure and disable balancing on the BMS.
Ironically in two months even your small power supply could have top balanced your pack.
 

time2roll

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As long as they are fully assembled with a BMS it is fine to charge in series to the point of high cell voltage disconnect.
Set your charging voltage low enough to where there will be no disconnect. You can boost any low cells individually while the battery is connected in series. Or get that 5A active balancer and let it work. Still may take an extended time but you can use the battery while this works itself out.
 
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Very low, it is 175mA as far as I can remember.
175mA isn't too shabby.
From memory JBD is 150mA and Daly is 30mA.
With a decent charge profile and judicious bandwidth management folks are making commodity cells work with the JBD BMSs.
You may or may not need an active balancer.
Are your cells swollen?
Are the QR codes ablated or otherwise obscurred?
Did you capacity test?
 

noenegdod

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I have spent good amount of money to buy these cells and since last 2 months they remain unused due to this balancing problem. It is difficult to take it off and put it on the bench to balance, I am wondering if buying a 5A balancer is a better choice at this point instead of faffing with tiny cells and waiting for ages for the top balancing. What do you suggest?
Yes, If you have the money, get a high current active balancer and just move on and forget about it. Parallel top balancing is a complete waste of time unless you dont have the $120 to buy an active balancer.
 

atti

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While I try to top balance manually, I can use the time and order an active balancer from China if someone can recommend me a good one. It is taking eternity to receive good here from China.
 

Just John

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Must add that I would have lost more money as the system is not in practical use, so any cornering cutting seems pointless to me.

These work reasonably well:


They are the same, one is just on Amazon for lots more money and also will arrive fast.
They also offer different (faster) shipping speeds on Aliexpress, you just pay for it.

When you get near the top, just use low current and you can be top balanced quickly.
 
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