Too late to top balance with BMS?

[kolek]

Why don't you just have all 16 connected in parallel?

I think you can only parallel cells if they are within a certain number of volts to each other. If someone else who knows can chime in....

 

[alcook62]

I think you can only parallel cells if they are within a certain number of volts to each other. If someone else who knows can chime in....

To achieve a good top balance you should have all 16 cells in parallel while doing the top balance. You may be confusing this with paralleling multiple batteries. If you parallel two or more batteries they should be as close to the same state of charge as possible to avoid a large inrush of current (big scary spark!) as the batteries seek to enter a state of balance.

 

[Ampster]

That won't achieve a top balance

If you define a top balance as balanced at 3.65 volts I suppose that would be correct. However 3.45 volts is far enough up on the steep part of the charge curve that it will be sufficient for most purposes. There is very little capacity to gain from charging to 3.65 versus 3.45. They are going to settle at 3.33 anyway.

 

[Checkthisout]

If you define a top balance as balanced at 3.65 volts I suppose that would be correct. However 3.45 volts is far enough up on the steep part of the charge curve that it will be sufficient for most purposes. There is very little capacity to gain from charging to 3.65 versus 3.45. They are going to settle at 3.33 anyway.

You want to top balance to 3.65 volts.

After putting into service, you can daily cycle to 3.45.

 

[S Davis]

I've been trying to top balance a 16 cell battery in sets of 4 (in parallel, using a charger), but it's taken 1 week and I've made little progress on the first set of 4.
Here are the voltages of the 4 cells I have tried to charge:
3.343V
3.340V
3.333V
3.332V
(They didn't charge evenly because for the first 5 days of charging, I had the both the positive and negative charging wires on the terminals of the first cell, rather than splitting it between the 1st and 4th cell).

All the other cells are about 3.292V.

The charger is a 60A charger but it's charging at about 4.5A, I'm using 18AWG wire. LF280 batteries.

Is there too big a difference between these cells to just use my JK-BMS to charge all 16 cells together?

At this stage what's the best course of action? Charging in sets of 4 is going to take a month or more at this rate.have put together 8-4s

If these are 280ah each set of 4 cells will take between 68-72 hours, I have put together eight with a 30volt 10amp supply charging at 10 amps.

So around 280 hours.

 

[kolek]

You want to top balance to 3.65 volts.

After putting into service, you can daily cycle to 3.45.

@Checkthisout
I'm not doubting you but could you please explain why it's better to top balance to 3.65V?
Seems like some people believe charging to 3.65V and letting the amps drop to zero is doing damage to the cells.

 

[time2roll]

60 amp charger with some fat cables can get all cells together in parallel 3.400 - 3.500 zone fairly quick to assemble the battery.
I assume the JK has active balancing and will take care of the rest while in service.

 

[kolek]

@time2roll
Yep, I'm working on it. Thanks for the tip!

 

[Checkthisout]

@Checkthisout
I'm not doubting you but could you please explain why it's better to top balance to 3.65V?
Seems like some people believe charging to 3.65V and letting the amps drop to zero is doing damage to the cells.

So that each cell gets full. Think of it as the same thing as equalizing cells in a lead acid battery.

Except with the lithium cells, you only do it once.

Do it however you want. If you want to top balance at 3.4, do that.

 

[kolek]

Guys, you were right. I switched from 18awg to 8awg wires, and now I'm charging at 17 amps. An increase of 13amps over what I was getting with the thin wires. Thanks to everyone for the advice.