Cell voltage imbalance only when fully charged

[MisterSandals]

My problem may be just settings, perhaps not the cells.

Did you do a "read" before changing values and trying to write?

 

[Levo]

Okay, firstly I need to adjust the "start voltage" on the app. I enter the revised start voltage on the balancer (3420mv) but the app will not let me write the value to the BMS - does not retain it. I don't know how to get by the error message. I did purchase the app for $10 CA (iphone). Last year I could only find the overkill app for android.

I just checked; looks like overkill now has an app for iphone. Shall try that rather than wrestle with Xiaoxiang. Thanks

My problem may be just settings, perhaps not the cells.

 

[Levo]

Did you do a "read" before changing values and trying to write?

Yes, have read and re-read many times. Just can't figure out the "cycle count"error. I am not very good with this iphone sstuff!

 

[MisterSandals]

Shall try that rather than wrestle with Xiaoxiang. Thanks

I hate receiving this advice myself but... have you tried removing the app and downloading a new version?
The number of times this has helped me on iOS is very low. The number of times on Android is very high.

 

[Levo]

Yes, have read and re-read many times. Just can't figure out the "cycle count"error. I am not very good with this iphone sstuff!

Okay, just switched to overkill, (which I could not find for iphone last year). It was easy to adjust the start value and is actively balancing now. Maybe it'll do the trick. Thanks for mentioning that

I hate receiving this advice myself but... have you tried removing the app and downloading a new version?
The number of times this has helped me on iOS is very low. The number of times on Android is very high.

Okay, just switched to overkill, (which I could not find for iphone last year). It was easy to adjust the start value and is actively balancing now. Maybe it'll do the trick. Thanks for mentioning that. I appreciate your help.

 

[Warpspeed]

With that inbalance at only 27 battery volts I suggest using a DC resistive load across the high cell and manually discharging energy whilst observing cell volts via the app. An automotive 50 watt automotive bulb is a useful load. Apply across the high cell for 10s of seconds at a time.

Mike

That is the way to do it.

Let the cells charge up normally, to whatever voltage you have decided will be the full normal daily charging voltage.
When charging current has fallen to zero, place a resistor across the highest voltage cell and bring the voltage down.
Only do one cell at a time, and only use low current, so the discharge is very gentle.
I use a one ohm resistor (nominally 3.45 amps or so discharge).

When you have done that, leave it alone, and let the whole battery go through another normal night time discharge and another daily charge.
That high cell will still be high, but not as high as it was before. Rinse and repeat.
Always go for the highest voltage cell for the next controlled discharge, and only correct the one cell each time.

While you are doing all this, if one cell is much lower than the others, do the same thing by charging just that the one cell at a very low rate to bring it up equal to the others.

All this can take some time, but once the whole string is balanced, it will pretty much stay that way for a very long time (many months).

The secret to success is patience and only very gently correct one cell at a time.

Let the battery work normally through several charge discharge cycles, and the whole thing will gradually settle down.
If you try rushing it, by charging and discharging several cells at the same time, your voltages will be all over the place after a couple more charge discharge cycles, and it will all be a complete waste of time.

You want your cells balanced at the normal daily full charging voltage, NOT at 3.65 volts, which is the absolute safe maximum voltage.
I charge to 3.45v and what happens beyond that is of no concern, because the cells never see a higher voltage than that.

Be patient, be very gentle, and let the cells settle into their normal daily working routine and if you balance at full normal charging voltage, they will then pretty much stay that way.