alt.energy.homepower

"(PeteCresswell)" wrote in message
news:c5ijs39mg1hg6flkr4upf6ioev26g267jm@...
> Posted here bco the obvious expertise of group members in matters
> electrical.
>
> Bicycle-mounted front wheel generator (alternator?) hub - puts
> out AC.
>
> Numbers on the hub say 6 volts, 4 watts.
>
> Putting a volt meter on it, I get 3v at walking speed ( mph),
> 6v at 5 mph, and more as speed increases. With me on it, I
> don't see it ever getting up to 20v, but 10-12v could be fairly
> common.
>
> From what I've heard, there is a problem with using bulbs wired
> direct. You get a bulb that won't burn out at the higher
> voltages, and it's dim where most of the riding happens - at 5-10
> mph. It also goes out when the bike goes really slow or stops.
>
> I'm basically clueless re/electrical stuff, but what I've gleaned
> so far is this:
> ------------------------------------------------------------------
> 1) Something called a bridge rectifier will convert AC to DC.
>
> 2) If I put a couple of NiCad batteries end-to-end, but
> across the rectifier's output, they'll be charged when the
> output exceeds 3 volts and supply 3 volts when the output is
> less than 3 volts - limiting the voltage that any bulb or
> LED emitter is subjected to about 3 volts.
>
> 3) There are myriad 3-volt LED lights out there that I can choose
> from for the lighting part. Red, white, steady, flashing....
> you name it, somebody's selling it.
> ------------------------------------------------------------------
>
> Bottom line, I want maximum brightness when just noodling along
> at 3-7 mph, but don't want tb burning out bulbs if/when I go down
> a hill fast.
>
> My primary concern is the lighting that's visible to closing
> traffic from my back. I avoid roads with any significant amounts
> of traffic, but even in the quietest neighborhoods and parking
> lots there's some exposure.
>
> The more light and the more attention-getting on the rear the
> better, since I'm competing with cell phones, text messages,
> email, and navigation screens.
>
> I use a hand-held flashlight for the front lighting and it works
> well. (Lowe's TaskForce 4w LED... one *brave* little flashlight)
> .. but I also want a token front light attached to the bike and
> wired into the system in case some cop wants to get technical or
> the hand-held fails when I still have to get back to my home.
>
> Am I on the right track? Seems like the capacity of the
> rectifier would be a half amp max (4w/20v + fudge factor).
>
> One more time: I'm clueless about electrical stuff.

You could just use the diode output feeding to the battery, with a switch to
disconnect the generator when the batteries are charged to avoid overchargeing.
Overchargeing can destroy the batteries. If your light dims, flip the switch on.
You would need to measure the generator output into the battery to determine the
chargeing rate, to know how long to charge each time.