Keith,
Unfortunately, charging a 48v series string of batteries undercharges the weakest one and overcharges the fullest one. Something about internal resistance being proportional to voltage, but in the wrong direction for naturally balancing batteries.
This is true for lead-acid chemistry, but reportedly not true for some lithium chemistries. Lead acid cells naturally and slowly diverge over charge-discharge cycles. That is why flooded lead acid batteries are "equalized", or more accurately, severely overcharged, so that each internal cell of the battery is absolutely full, or equal in voltage to it's neighbor.
AGM lead batteries should not be severely overcharged... it drives off the irreplaceable moisture. That is why AGM smart chargers are required for long-term AGM battery health.
It would be marvelous to have a BatteryManagementSystem that took what little regen was available, and stuffed it into the weakest battery.
Gonna sail Constance (e-H55) monday.
Mark Stafford
--- In electricboats@yahoogroups.com, "aweekdaysailor" <aweekdaysailor@...> wrote:
>
> Thinking about the case of a weak battery in a string (say 4x12)...
>
> In the above scenario (and there is _always_ 1 weak battery in a string...) - isn't any 48+V charging source selectively charging the weak battery (more charge acceptance)?
>
> Sailing around in good wind this weekend and getting 1-2amps regen pretty consistently according to my CycleAnalyst...it ain't much, but when I did have to motor up, it seemed that my voltage stayed higher, for longer, than this small about of charge would account for...which got me thinking....
>
> Since the weak battery ultimately determines the effective voltage of the string (and hence your range) - is it possible that just looking at overall watts in isn't telling the whole story? Can we capitalize on that (BMS system, etc)?
>
>
> -Keith
>
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