TS quote 4.2v as the fully charged maximum. This circuit turns fully on at 4.13v with the pot setting I use - the voltage gain is enormous with two darlingtons - so the voltage can't go any higher than that. Others are using a lower voltage for maybe two reasons: their circuit doesn't turn on so quickly, or, they are just being more conservative on the upper voltage limit. If you look at the TS charge graphs, the voltage is limited to 4.2v and held there for 70-odd minutes as the current falls to zero. At the time point where 4.2v is reached and the current starts to drop, the % charge is only 70.
The main reason I dropped it from 4.2v to 4.13v was that I read Tesla Motors have dropped their max charge voltage for 18650 cells from 4.2v to 4.15v "in the interests of increased battery life".
I have noted that if I charge the cells at 3.7V until the current drops to zero, then increasing the voltage to 4.2v causes a current flow (at the 6A limit) for only another 10 minutes or so, so they must be close to fully charged at that voltage.
the difference in recoverable AH, between charging to 3.4v and 4.2v is 2.5%, based on the bench testing i did on a single cell (TS 40AH) a while ago.
from a BMS design perspective, charging only to 3.6vpc with a 4.2v limit reduces complexity somewhat (dont need to shunt full charge current).
you can also use more cells on the same peak voltage rated controller
it also increases charge efficiency, as you wont *have* to balance on every single charge.
as far as the effect on cycle life, im still figuring that one out (ive been charging to 3.6v for more than a year now).
Nevilleh wrote: As far as my car is concerned, I also wonder if I use 4.2v per cell as the max charge voltage, the whole pack of say 46 cells now produces 193.2v instead of the nominal 3.2x46 = 147.2. Sure it's only for a few minutes, but can my 156v rated controller handle that?
I'd be interested to other opinions.
if the logisystem guys are still using 200v parts, then starting at 193.2v is indeed a little dangerous. a little overshoot on the powerstage and BANG.
that takes about 1 sec.
if you let your bms pull the pack voltage down before starting, you should be fine.
Id ask the logisystem guys what the max operating voltage of their controller is.