Overkill BMS - quick question regarding balancing

[John Frum]

Just re-read the thread and you’ve highlighted that I should only be balancing while charging and above float voltage. I don’t recall what the charge voltage is but absorption is 14.2 so assume that to mean it charges to that point. Now, float is set to 13.5 but the BMS balancing is set to start at 13.4. Might need some fine tuning.

First picture is the BMS configuration, second is the charge controller.

Ok you are charging to 14.2 which is good.
Try incrementing by .1 volts every few days to to see if the balance improves.
14.6 is dead full and you will probably get a high cell disconnect if you try for 14.6.
I would stop at 14.4 volts.
Set the charger to float at 13.4 or lower and set the bms to start balancing at 13.5.

 

[Gould]

Done, I’ll report back in a couple of days.
Thanks again!

 

[Pierre]

Unfortunately cell balancing in most BMS ‘ s , including the JBD , is a non event. They are mostly passive balancers and reduce voltage in higher cells but not giving to lower cells like active balancers - so do not hold your breath while the JBD ‘balances’ at 30mA.

 

[Gould]

Been watching closely as they charge up this morning, they just reached absorption with the new 14.3v setting. There is balancing going on, as you can see cell one is quite a bit off.

 

[John Frum]

Been watching closely as they charge up this morning, they just reached absorption with the new 14.3v setting. There is balancing going on, as you can see cell one is quite a bit off.

Just want to confirm.
You are no longer balancing at float voltage?
And your are not balancing on discharge?

 

[Gould]

Correct, there is no balancing at float nor is there balancing at discharge. There is balancing at absorption but I think that’s fine.

 

[Gould]

That said there doesn’t appear to be any further balancing going on now.

 

[John Frum]

Correct, there is no balancing at float nor is there balancing at discharge. There is balancing at absorption but I think that’s fine.

That is as good as it gets.

 

[John Frum]

That said there doesn’t appear to be any further balancing going on now.

Is there any charge current going into the battery?

 

[Gould]

no, nothing going in

 

[John Frum]

no, nothing going in

Your bms only balances during charging.
That means current going into the battery.

 

[John Frum]

Anyways your top balance is fubar.
Remedial action is required.

 

[Gould]

That’s what I figured. Make sense to tear down the pack and rebalance? I am working with with the distributor to see if it’s a bad cell.

 

[Gould]

Until then am I right in my thinking, that the battery will be limited to the capacity of the one cell? And because it’s paralleled with another, the entire pack will but just as limited? I have a number of trips planned in the coming weeks so don’t know when I’ll be able to re-balance. Just want to confirm I won’t be hurting anything if I continue using.

 

[John Frum]

Until then am I right in my thinking, that the battery will be limited to the capacity of the one cell? And because it’s paralleled with another, the entire pack will but just as limited? I have a number of trips planned in the coming weeks so don’t know when I’ll be able to re-balance. Just want to confirm I won’t be hurting anything if I continue using.

Worse than that.
In a properly top balanced pack the capacity is that of the weakest cell.
In your case it will be less than that.

 

[John Frum]

That’s what I figured. Make sense to tear down the pack and rebalance? I am working with with the distributor to see if it’s a bad cell.

If it was me I would not tear down the pack.
I would top off each cell individually while still in the pack.
Current flows back to its origin so if you attach the leads via alligator clips so that the path to source only goes through 1 cell you can do this.
Make sure you get the polarity correct though.
If you are uncomfortable doing this then break the pack though.

 

[Gazoo]

I have turned off "Balance While Charging" and set the BMS delta to 5mv's with good results. This will only work if the cells are resting. Once the cells are balanced, then I turned on "Balance While Charging" and then charged the battery. Once the battery was charged, I set the BMS delta back to 15mv's. I wanted my delta to be as low as possible at 3.40 volts, so I set the BMS balance to start balancing at a lower voltage...I think 3.35 volts. The only problem is when a BMS parameter is changed, it will throw off the capacity reading and then a full cycle must be done to get an accurate reading.

Until then am I right in my thinking, that the battery will be limited to the capacity of the one cell? And because it’s paralleled with another, the entire pack will but just as limited? I have a number of trips planned in the coming weeks so don’t know when I’ll be able to re-balance. Just want to confirm I won’t be hurting anything if I continue using.

I would do as smoothjoey suggested. Turn off BMS balancing while doing this. It's going to be the quickest way to get your cells in balance.

 

[Gould]

Appreciate the direction here for sure. Admittedly I’m a little nervous charging a single cell, really have no idea what I would be doing and see too much that can go wrong. I may run off of the single battery for now until I can tear it down and re-balance.

 

[Gould]

Last note on this. With the charge voltage increased to 14.3 two of the cells were steadily climbing, sitting at 3.625. I’ve dropped the charge voltage back to 14.2.

 

[John Frum]

Last note on this. With the charge voltage increased to 14.3 two of the cells were steadily climbing, sitting at 3.625. I’ve dropped the charge voltage back to 14.2.

So if 2 cells are climbing does that mean the delta is decreasing?