Are these cells top balanced?

[LucianM]

Hi,
I have built a 24V / 280Ah battery with JK BMS that has 2A active balance.
Initially I wanted to charge it to almost full, then put the cells in parallel and charge them at 3.6V.
But then I noticed that they seem quite close regarding SOC and got lazy, so I've let it charge at 28V and balance for a few days.
Now it looks like this, there is almost no current going in.
Do I still need to put them in parallel or this is enough?

 

[brum]

These seem balanced. Several days with the 2A active balancer would be pretty sufficient to fully balance them.

 

[chrisski]

I would still top balance because measuring voltage is unreliable for seeing SOC.

You're 8 hours away from having this top balanced, including setup, tear down, and charge time.

My profile will only balance above 3.45 per cell and needs to be charging. How many amps it balances is a mystery. I charge to 3.475 volts per cell, so not much time is spent balancing cells. I have no idea how long it would take me.

You have a better balancing profile having a top balancer installed. I don’t have that.

All depends how much 8 hours now is worth possibly tearing down and top balancing later.

 

[LucianM]

I would still top balance because measuring voltage is unreliable for seeing SOC.

My understanding is that voltage measuring is unreliable when you are on the flat part of the charging curve, but 3.5V is already on the steep end part.
As an experiment, I increased the charging voltage to 28.2V and the cells quickly stabilized around 3.5V, with almost no current going in.

 

[chrisski]

My understanding is that voltage measuring is unreliable when you are on the flat part of the charging curve, but 3.5V is already on the steep end part.
As an experiment, I increased the charging voltage to 28.2V and the cells quickly stabilized around 3.5V, with almost no current going in.

View attachment 130588

Honestly, with a 2 amp active balancer, it would probably be good, but to me it’d be worth the 8 hours of my life to complete a Top Balance for peace of mind.

Just the way I’m wired.

 

[HighTechLab]

My understanding is that voltage measuring is unreliable when you are on the flat part of the charging curve, but 3.5V is already on the steep end part.

Your understanding is correct and your cells are indeed close enough. Top balancing is good when you are much further apart than the BMS can handle initially... which is not the case here. if it were my pack, top balancing wouldn't give me even a fraction more peace of mind. I've messed up more times top

 

[TomC4306]

My understanding is that voltage measuring is unreliable when you are on the flat part of the charging curve, but 3.5V is already on the steep end part.
As an experiment, I increased the charging voltage to 28.2V and the cells quickly stabilized around 3.5V, with almost no current going in.

View attachment 130588

4 mv at 3.5 volts= well balanced.
Done