Myles,
I am still struggling through understanding batteries, but after struggling with a sick pack for a couple of years I think what we really want is a balancer that works on discharge.
Even if you equalize all the batteries to the same voltage - that doesn't mean they will perform equally on discharge. A sulphated battery will have greater sag and internal resistance and as the pack discharges the delta between it's voltage and the other batteries in string will get higher and higher. Eventually, it will get into the cell-reversal range.
So I think we need the Anti-Lee Hart shunt - one which open connections to good batteries when a weak one is detected and that current then used to boost the weak ones.
Somewhat by accident I think I have this - my batteries are arranged as 4 banks, 3-batteries in parallel for each (node?) in the string. If any one battery is weak, the other 2 in parallel ought to be holding it up to their combined voltage (right? I hear stories about odd current paths and wonder..). So it's the average of the paralleled batteries which "appears" in the combined string voltage. The odds of a single battery taking the whole pack down are reduced.
Similarly...I am now using a 48V charger - and the good batteries will be constantly drained by any weak one in the parallel bank.
The alternate wiring - that of 3 48V strings in parallel - would not be able to do this as the good strings wouldn't "see" the weak battery since the strong ones will just take a slight excess charge (the charging problem all over again).
I have seen some "laddering" techniques where the 3 parallel strings are cross-connected at multiple points (vs just the ends) - this would seem to be another route to the same effect (won't work as well on my boat due to cable-length issues)
With occasional re-balancing this seems like it ought to work, but there are people like yourself with way more actual knowledge (vs guesswork) thinking about this on the EV/Solar forums.
So I guess what I am asking is...critique this method of wiring. Is there a benefit to parallelism within the serial strings? Or is it really causing problems due to weirdness that I can't foresee?
Thx
-Keith
--- In electricboats@yahoogroups.com, "Myles Twete" <matwete@...> wrote:
>
> As an alternative to multi-chargers:
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