MR> I think that it's not worth it according to my calculations. For example
  > say one used 4 x AA's of 100mA/Hr capacity... to just run the light
  > during a 2 minute traffic light (2/60 x .5A = 16mA/hr) one would have to
  > recharge at a safe 20mA/Hr (C/5) over more than 50 minutes!!!

MR> To use a larger capacity say 4 x C at 500mA/Hrs also adds a lot more
  > weight. The calculation for C size changes a bit since we can now charge
  > at 100mA but the recharge time still takes over 10 minutes PLUS the extra
  > muscle power (almost 1 watt).

You may be right about it not being worth it, but I'm wondering about the 
source of your battery capacity numbers. Most AA NiCd's that I've seen 
claim 600mAH, and I have a few better than average ones that claim 800. 
My NiCd C cells claim 1500mAH. These might also be slightly above average, 
but are still not the more expensive "high capacity" cells.

So, for garden variety NiCd AA's, a C/5 charge is 120mA, C/10 is 60. And 
if your charger is smart enough to know when to quit, you can push them 
harder for short times. Not that you'd actually want your charger sucking 
up several watts of pedal power. But a really smart system that can jacks 
up the charging current when braking or going down hill could be good. 
Now that I think about it, it really wouldn't have to be all that smart. 
Maybe a switch on one or both brake levers, such that the switch closes 
before the brake pads make contact. Squeeze just a little, and the charger 
cranks up the current and creates a bit of drag. Which, of course, is 
usually what you want when you lightly squeeze the brakes. This should 
work for both hills and stops. Changing your riding habits to make 
longer, slower stops could improve it a bit. Charging at a less noticeable 
rate during daytime riding is another possibility, or better yet, with a 
solar cell.

Of course, NiMH's are much better still. AA's I've seen range from 1300mAH 
to 2200mAH with most common ones of recent manufacture falling in the 1800 
to 1950 range. The 2000+ ones can be significantly more costly. AAA's are 
700 to 800mAH. C's are a whopping 3.5 to 4.5AH. And D's are 8 to 9AH.

MR> I was toying with the idea of a small 5 volt dip relay that would switch
  > to a set of 4 x alcalines during stops but the extra bother doesn't seem
  > so worthwhile the more I think about it.

MR> One would be better off with a small rechargable 2-cell Lithium pack and
  > a wall wart... forget the dyno! After the night ride just plug in the
  > battery pack and that's all.

I agree. Or even ordinary NiMH, since those are still pretty decent power 
to weight ratio and will drop right in to any bike light that accepts one 
of the more common cell sizes. 

Heck, even carying around a 2 pound SLA battery would probably be less 
work than pushing a generator. That's about the weight of the 6V, 5AH SLA 
batteries sitting on the shelf next to me. Bad power to weight ratio. 
Good power to cost ratio.

And you can always use a solar powered charger if you're feeling green.


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