"Tim Wescott" wrote in message
...
E. Walter Le Roy wrote:

We have a 7 foot water wheel in a mountain stream and would like to hook
up
an alternator, and light up the fish pond. Can anyone tell me what RPM
it
needs to turn to run one headlamp?
Thanks
Walt


The alternator, or the wheel? What sort of headlamp?

Given that most automotive alternators seem to be driven at about 2x the
crankshaft speed, and the engines idle at least 500 (probably more like
750 or 1000) rpm I'd say you need to give it at least 1000 rpm.

I'm not sure how your average automotive alternator would do without
working into a battery -- I'm sure a regulator could be built that would
allow you to run without one, but it'd be a bit of a science project.

[snip]

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Actually, most alternators are not self-energizing and as such, without
a battery, you don't get anything back out (in a normal alternator, the
battery voltage is applied to the rotating field coil and the resulting
output is rectified and fed back into the battery). There are some
self-energizing alternators (I have seen them in a marine environment),
but I don't think you will find them on cars. That is a big difference
between the alternators and the older cars with generators -- if the
battery was totally dead, you could push the car up to speed and the
generator would kick in and you could drive. With an alternator, if
the battery is totally dead - you're dead.

mikey