At what voltage to begin balancing and why?

[ironhalo]

I’ve seen differing opinions on what voltage to allow your BMS to begin balancing while charging. Can someone explain to me the theory behind making the that decision for your custom packs?

My current pack is a 20s12p pack of Samsung 50E2. So 72V/60ah. My charger is a 72V/10A (84V) charger. The default value in my BesTech BMS for when to begin balancing is 2.5V/cell but that seems really low from the conversations i’ve read here. Most people say north of 3.0V. There is another setting i believe which starts balancing if the maximum delta between any cells is .5V. Both settings are adjustable.

How do I decide the optimal settings for my scenario? Thanks in advance.

 

[jonescg]

Bestech BMS modules are pretty basic. I think they start balancing at 4.15 V. So if you charge to 4.2 V per cell, it will eventually balance down to 4.15 V.

 

[ironhalo]

Bestech BMS modules are pretty basic. I think they start balancing at 4.15 V. So if you charge to 4.2 V per cell, it will eventually balance down to 4.15 V.

Not this one...HS-017. Has a ton of options, including the two I mentioned above.

http://www.bestechpower.com/communicationbms/HS-017.html

 

[john61ct]

Balancing can work just fine at any voltage.

Usually just below or just above your chosen normal working range.

If top balancing, while charging, then starting lower gives more time, since the balance current rate is usually piddly small

and it is not good to sit at high SoC longer than necessary.

But manually balancing at the midpoint is good too, so long as you're using per-cell voltage for dis/charge termination at both ends.

With good quality healthy cells, may not need to do it very often, few times a year.

 

[jonescg]

Neat - they've come a long way.

In that case I'd still leave the commence balance voltage as 4.15 V. Unless you can do a dynamic balance, where it looks at the average voltage at any state of charge and only balances those which are more than 0.05 V above the mean.