[links] OT

On Tue, 17 Apr 2007, Karel Kulhavy wrote:
> What computer are you using? I am building an exercise bike generator and I
> want to connect a PC or laptop to mitigate the unhealthy lifestyle connected
> with computer-based occupation. 
...I was talking about an old 486 VESA bus no-name, but I think the go
would be a laptop so that its battery would act as a UPS between pedal
strokes.
> 
> At the moment I have a 60W SEIG (self excited induction generator) from an
> ordinary 60W three phase asynchronous motor, which can light a 60W light bulb
> (though not full shine) when powered by an electric drill.
> CL<
...Amazing! I built just such a rig many years back. I did not know that
you called the generators SEIG, even after doing years of research work on
them.  see http://www.flowtrack.com.au
The biggest problem I had was that the pedal generator had a horrible
speed/torque curve and tended to go through excitation/de-excitation
cycles as you pedalled harder and softer. This could be sorted out by
either having more flywheel on the cycle, or by fiddling the generator
voltage with a transformer or star/delta rewire if possible. 
The permeability of the generator magnetic circuit starts low
(1000) then gets good at operating voltage (10,000) then falls off
again. This means excitation voltage is very unstable until it gets up to
about normal, at which point you are wasting a lot of puff just exciting
the thing.

The problem will be made worse however by the switchmode power supply you
get with laptops. They will typically work on 100 to 250 volt, and be
unfussy about frequency, but they have negative marginal impedance - the
slower you pedal the harder it gets. This means they will pull down the
voltage to the lowest functional point and probably run erratically in
some brownout/start mode. I would try it on an expendable laptop supply!

Regards
Kali


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