bms (by definition) not allowing for low(er) voltage charge

[timmy66]

I've looked through a few functional diagrams for BMSs -

it seems that if one desires to charge to 4.1V (on INR18650s), that it's basically impossible to ensure that the voltage spread will be correct.

Further, if wishing that the proper CC/CV curve be followed, this definitely won't be happening - neither the summed voltage of a 13s4p pack would represent the "weakest" parallel cell group, so all bets on the proper termination current would be off for that group that didn't hit the total_voltage / num_cells (eg, 4.1 / 13s = 53.3 V).

And in general - even if charging to a "full charge" on a bulk voltage, it seems that it's also unlikely that the proper individual cell-group currents are falling into the proper C/10 current rating given to a cell group in the CV state.

Am I missing something? So if trying to get reach data sheet theoretic charge cycle maxes, a BMS (ones I've reviewed) are never going to allow this, as the batteries are never being treated according to how they should be charged.

 

[Sunder]

Get a programmable BMS and you can basically do what you want.

The BMS will never do the CC/CV part for you though. That's not its job. Your charger will have to do that.

 

[dogman dan]

The easy solution is a more multi charge voltage charger. The satiator from grin is one, but others like EM3ev sell bulk chargers with a three position switch.

One position half charged, for storage, another is a slight undercharge, the last a full charge.

The way I used mine, was to charge to 4.1v most of the time, and occasionally charging to 4.2v to have longer range, and balance the pack. If you use your battery in a conservative manner, it will retain balance a long time despite charging to just 4.1v. Balance it any time you run it till the bms shuts it off though.