Thx Mark,
I thought the series charging problem was more a "rising tide floats all boats" - so the string gets up to full voltage only by over-charging the 3 good, but the charger cuts out before the bad one gets up to full voltage. But charge acceptance in the bulk phase is higher in the weak battery (right?)- so it perhaps does get more watts proportionally, but not before the (conventional) charger cuts out, leaving it at a lower voltage than it's peers (I have a weak understanding of all this at best...corrections appreciated)
I also think I remember someone (Arby?) stating that the method of regen charging from brushless controllers is a high-voltage pulse - in which case there's no 'cutoff' voltage.
But...I didn't expect to get anything "free" out of this - just got me thinking that if we could use regen on the weak batteries, the effective increase in range might be "good enough" to justify some effort and expense in having it work. (but a discharge BMS provides the same benefit...)
Maybe enough Leaf's will crash out of the fleet in the next year we don't need to worry about it :)
-K
--- In electricboats@yahoogroups.com, "Mark n Angela" <mstafford@...> wrote:
>
> 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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