you can (and I have done this) use isolated DC-DC convertors to run floating charger ICs to charge each individual cell in a series string. I can give you a block diag if needed.
Wow, i have been wondering if there's some way to DIY a balanced charge on series batteries, using separate chargers! I would love to see that block diagram! That would be great!
You're using the DC-DC's to isolate the cells, so to the load they appear to be series instead of parallel, right? I mean, we're not really needing to convert to a different voltage-- we just need isolation, right? So, could we simplify further, and just use a single power transistor on each cell to isolate?
Cost is the main issue (hence why i'm compromising with the linear charger, above).
- My current scenario is 1 linear ~16V pcb, no balancing, about $6.50
- I could also get a single pcb, 4-cell balancing charger for $10
- This scenario is 4 ~4V linear pcbs + 4 DC-DC's. I can find the pcb's for about $0.70, and the DC-DC's for about $1.30, * 4 cells = $8. Too high, compared to above options. But if i can get away with just a power transistor for <$0.75, then i could beat the above methods on cost, and get balancing. That would rock.
We'd still want our common supply V to be Number of Cells * 4.2V+, right?
Incidentally, i realized that even if i use protected cells, that will not give me the charging slope that li-ions require, so i believe still need to use a charger pcb-- in which case, the protection is superfluous. Is that correct?
thx!
(should we start a new thread for this?)