Active Charging to replace Active Balancing

[Riplash]

Hello All,

There has been a lot of discussions recently about passive balancing versus active balancing with a B.M.S. But I haven't seen any discussion about balancing a pack by charging only the lower cells. Do any of the B.M.S.'s or charging systemsthat are used for Powerwall's do active or smart charging?

For instance if I had a 14S battery and all the cells except number 5 were at 4.10 volts, and cell number 5 was at 3.90 Volts. I would attach a localized charger to charge cell bank number 5 to 4.10 V and not charge the rest of the cells. If I design a BMS and Charge Controller, I would have it measure all the voltages of the cells, and if a cell is so far lower than the average voltage of the cells in the rest of the pack, I would have the bms/charger just charge the lowest cell till it is brought up to the average cell voltage.

Do you know if any of the systems that are used for Powerwalls do this? Or what some of the advantages or disadvantages of doing thiswould be?

Thanks,
Ryan

 

[Crimp Daddy]

At first I thought of a hobby charger but unfortunately hobby chargers wont do that job autonomously.

That said, you could connect that device to a cells, and bring up the cell voltage like you mentioned manually. Some of my packs do not include a BMS, but occasionally I would connect a hobby charger for pack maintenance and balancing if the cells started to drift a significant amount.

Alternately, if the packs very large, you could probably just initiate a balance charge and walk away for days on end and if it never terminates, it would just keep running almost be like a full time active monitor / balancer.

I think it would be possible to build what you are talking about even with something like TP4056 modules and some type of isolation device, and an Arduino or similar PLC for control but its beyond my paygrade. Check out these videos series charging with TP4056 modules might put you in the right direction.

 

[completelycharged]

Some "active" balancers effectively do that but are powered from the pack as a whole to charge the lowest voltage cell in the pack, switching each cell onto a common bus one cell(p) at a time. I had an active balancer unit, although it failed and the design resulted in a cascade switching short circuit across each set of cells... still waiting for the return dispute to be fully resolved 2+ months on...

 

[Riplash]

At first I thought of a hobby charger but unfortunately hobby chargers wont do that job autonomously.

That said, you could connect that device to a cells, and bring up the cell voltage like you mentioned manually. Some of my packs do not include a BMS, but occasionally I would connect a hobby charger for pack maintenance and balancing if the cells started to drift a significant amount.

Alternately, if the packs very large, you could probably just initiate a balance charge and walk away for days on end and if it never terminates, it would just keep running almost be like a full time active monitor / balancer.

I think it would be possible to build what you are talking about even with something like TP4056 modules and some type of isolation device, and an Arduino or similar PLC for control but its beyond my paygrade. Check out these videos series charging with TP4056 modules might put you in the right direction.

Hey Crimp Daddy,

I do this by hand right now, meaning I am a human BMS and I hook up isolated TP4056 modules to the low cells. I am working, but very slowly on converting this to an automaticArduino and LTC 6804 or LTC6822IC chip. I am curious if any other powerwallers, or commercial products have worked on this.

-Ryan