Runner or not runner ?

[Zivva]

Here's my issue :

15S 200ah power bank (Rosen ...) with Seplos V1.

Cell 3 discharging faster than the 14 others. Reaching 2.8v when others are still @ 3.1 / 3.2v.

When charging, all cells get pretty well balanced (withing 5mv) in the middle of the curve, from 3.2v to 3.38v..

Then Cell 3 reaches 3.4v first before cells 14, 15, &16 take the lead and end up to 3.5 / 3.6v when the rest is around 3.4v. Once target voltage reached, cells 1,2 & 3 quickly drop to < 3.35v, cells 14,.15 & 16 remain pretty close to 3.5 / 3.6v.

If cell3 was a runner it would simply discharge / charge ahead of others but it's not the case here, so what would you think ?

Been trying different charging parameters with not much improvement.

Charging from 51v to 54v (default Seplos defsult setting / Rosen recommendation. Too high ...)
Charging amps from minimum (5A).to whatever available (50+). Seplos.limits to 10A when 1 cell reaches 3.4v
Float from 50.5v to 53v
Passive balance from 3.35v to 3.4v

Thinking about installing an active balancer or swapping the Seplos for a JK inverte with its own 2A balancer. Worth the hassle ?

Can't swap cells or try a top balance : busbar laser welded ...

 

[Suijkerbuijk]

My battery have a active balance i think one with a 2 amp model.
It really do fast balance the cells
On the moment 0.15 volt differences and it shutdown the charge and go balance the systeem and than reconnect back to charge.

On this moment its now set balance the systeem.
You see how fast it go just see time stamps on the bms.

Totaal time 15 min

 

[SeaGal]

Can't swap cells or try a top balance : busbar laser welded ...

Then if it were mine and you have half a day to spend on it, I'd charge up as far as possible to around 3.5V per cell. Then do a manual discharge of runners using a 12V auto light bulb, recharge to 3.5V per cell and then do a manual charge up of any laggers using a bench PSU.

See my postings in this thread for details...

One EVE 280Ah cell tripping BMS high voltage at top end

I have a self-built 280Ah 48v battery pack, that was working great. I initially did a top balance, parallel to 3.65v For a couple weeks now I've been having issues with one cell, #16 which happens to be my main positive for the entire battery. At the top end when the inverter is pushing the...

diysolarforum.com

One EVE 280Ah cell tripping BMS high voltage at top end

I have a self-built 280Ah 48v battery pack, that was working great. I initially did a top balance, parallel to 3.65v For a couple weeks now I've been having issues with one cell, #16 which happens to be my main positive for the entire battery. At the top end when the inverter is pushing the...

diysolarforum.com

 

[Zivva]

Then if it were mine and you have half a day to spend on it, I'd charge up as far as possible to around 3.5V per cell. Then do a manual discharge of runners using a 12V auto light bulb, recharge to 3.5V per cell and then do a manual charge up of any laggers using a bench PSU.

See my postings in this thread for details...

One EVE 280Ah cell tripping BMS high voltage at top end

I have a self-built 280Ah 48v battery pack, that was working great. I initially did a top balance, parallel to 3.65v For a couple weeks now I've been having issues with one cell, #16 which happens to be my main positive for the entire battery. At the top end when the inverter is pushing the...

diysolarforum.com

One EVE 280Ah cell tripping BMS high voltage at top end

I have a self-built 280Ah 48v battery pack, that was working great. I initially did a top balance, parallel to 3.65v For a couple weeks now I've been having issues with one cell, #16 which happens to be my main positive for the entire battery. At the top end when the inverter is pushing the...

diysolarforum.com

Thanks but I can't really see how to charge / discharge cells individually because of the welded busbars.

Actually a 15S4P setup with 4 cells of 50ah making 15 groups of 200ah ...

 

[Suijkerbuijk]

Thanks but I can't really see how to charge / discharge cells individually because of the welded busbars.

Actually a 15S4P setup with 4 cells of 50ah making 15 groups of 200ah ...

If you can not do it
Same with me i can not open the battery.
Its seal and marine battery .

What is do is slow charge it on a lower volt and bult up from that .
Just by adjust the float charge.
So really you need about 3.45volt on a cell
So what i have done go under it and than slow charge it up with just 0.5 volt extra on the Float.
This way i have balance my other battery .
Foto is from my other battery bank.

 

[SeaGal]

Thanks but I can't really see how to charge / discharge cells individually because of the welded busbars.

The points where the balance leads are connected will be the points between each individual "cell group"

 

[Zivva]

If you can not do it
Same with me i can not open the battery.
Its seal and marine battery .

What is do is slow charge it on a lower volt and bult up from that .
Just by adjust the float charge.
So really you need about 3.45volt on a cell
So what i have done go under it and than slow charge it up with just 0.5 volt extra on the Float.
This way i have balance my other battery .
Foto is from my other battery bank.

Float @ 50.8v allows the few highest cells to hit 3.45v, but the rest stay < 3.35v and the passive balancer barely do anything. +/- 2mv per day at best ...

 

[mikefitz]

and the passive balancer barely do anything

Under these conditions manually pull down the high cell with a dc load across the cell. Use a car filiment headlight bulb. Apply for several seconds whilst observing cell volts. Adjust duration as needed. Deal with each 'high cell' is turn.

 

[Suijkerbuijk]

Float @ 50.8v allows the few highest cells to hit 3.45v, but the rest stay < 3.35v and the passive balancer barely do anything. +/- 2mv per day at best ...

I do not know if you have to use it ?
Shut it down and leave it for 24 hours .
So it can slow do its job
Or use a multi meter and test the cells.
And use a light bol to pull it down
Nothing gone happens if you test the point you need with a multimeter.

If its open go for a active balancer .
And set that in.
That are all the tips people can tell you.

 

[Bob B]

Seems to me that if that cell is the first to hit the upper knee .... and is the first to drop off on the low end .... You have welded bus bars .... that cell is weaker than the rest.

 

[Zivva]

Seems to me that if that cell is the first to hit the upper knee .... and is the first to drop off on the low end .... You have welded bus bars .... that cell is weaker than the rest.

It's the first to drop to 2.8V, then the first to reach 3.4V (sometimes) ... before 3 other cells take the lead up to 3.6V when that cell and others stay @ 3.4V.

Typically when charging @ 52V or higher, all cells stay balanced up to 3.35V before one or more steadily get to 3.6V when the rest of the pack stays +/- @ 3.4V. End up with 250 mV deviation with 3 cells @ 3.65V, the rest @3.4V. That first to drop cell sometimes is the first to get to 3.4V but it has not reached 3.6V for a while. Just stays around 3.4V or few mV lower.

Trying charge @ 50.6V for now, in order to keep deviation low and hoping passive balancer to do (very slowly) its job.

That weak cell & 11 others @ 3.34V
Got 3 cells that reached 3.42V then lost 3 mV in the past 2 hours thanks to passive balancing ...