[nSLUG] Measured wattage of atom system

Dop Ganger nslug at fop.ns.ca
Thu Sep 18 09:49:20 ADT 2008

On Thu, 18 Sep 2008, Daniel MacKay wrote:

>> a bicycle/treadmill powered home server might [...] generate even
>> more heat in precisely the place I want extra
>> heat in the winter.
> Indeed it will - your booty.
> I'm sure i'll get corrected but to get the back-of-the-envelope
> calculations going: a hunky guy can produce about 3/4 hp sustained;
> that's a little over 500W at 100% generator efficiency.

A very hunky guy, of the order of a pro racer, to sustain that. I just ran 
some numbers through http://www.kreuzotter.de/english/espeed.htm based on 
my typical cruising speed along Barrington (ie, fairly flat) of 35km/hr 
and got back a wattage of 239W. I can for short periods (intervals, for 
those following along at home) run at 50 which gives 711W which looks 
rather on the high side but I suppose just about possible - that or I'm 
drafting more than I thought.

> Without doing any estimates or experiments I will make a guess that
> an ordinary person could probably produce a tenth of that in actual
> electricity watts, sustained.

I remember going to the Science Museum in London when I was a kid and 
pedalling on a demo single speed generator bike that was powering 25W 
bulbs and having no great problem lighting up 4 of them. Sustaining it for 
any length of time is where the difficulty lies.

And for anyone interested in actually doing this, the power output needs 
to be smoothed an awful lot depending on the application, so it's going to 
have to run through a battery or something, which will lead to further 
losses. http://www.los-gatos.ca.us/davidbu/pedgen.html has a fairly 
detailed study of a homebrew version.

Cheers... Dop.

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