> The point here is that batteries can't be recharged at the levels
> that rapid braking generates.

I previously calculated that the braking rate that you specified would 
require a 1/2 hour charge rate on a 40 AH battery.

You may wish to look at "AGM" (Absorbed Glass Mat) lead acid 
batteries. (Google knows). These have (I read) a real world charging 
capability of typically 3/4 of their rated AH value. eg a 40 Ah cell 
can be charged at the 1.333 hour rate. Still not enough. But going in 
the right direction.

It would be interesting to see how safe and reasonably sized a 
flywheel would be that took short braking peaks and stored them just 
long enough to lower the peak charging rate to something reasonable. A 
heavyish braking episode may last 10 or so seconds and for battery 
charging the power needs to be spread out over about 8 times that long 
(C/0.5 --> C/4). There MAY also be practicable short term chemical 
energy stores that would do this. eg a melted salt system with a heat 
engine to transfer the energy to the battery. Not nicely efficient 
alas. Carnot efficiency at 900K/600C is 66% and actual will be (well?) 
under 50%. You MAY be able to do crash electrolysis to Hydrogen but 
the currents seem excessive for the requisite mass and size.

Note that the model car racing fraternity crash charge their NimH in 
about 15 minutes - how much life they get, not matter how well 
controlled, i don't know. This is twice the rate required IF the 
battery is the whole system capacity.






    Russell McMahon

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