[clug] Exercise and pay the bills!

Alex Satrapa grail at goldweb.com.au
Tue Feb 10 00:31:01 GMT 2009

Some food for thought:

One guy's story, no recipe: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/08/23/HOKO11469A.DTL&hw=david+butcher&sn=001&sc=1000

Includes a recipe: http://www.humboldt.edu/~ccat/pedalpower/hec/hpeg/index.html

Cylec commercially available bike (Korean or Kenglish): http://www.cylec.com/

A narrative: http://www.pic101.com/solar/bikegen.htm

I love that first link - pointing out that the simple process of  
boiling the water for a cup of coffee was more work than the author  
could manage.

For reference purposes, a (white) MacBook draws 2.5W in standby (ie:  
lid closed, just charging the battery with a small maintenance charge  
for memory) and about 24W when it's running. I would assume an error  
of half the last significant digit on that meter (though my colleagues  
assure me it's bound to be within 10%).

How much power could you expect a human to generate? Depending on who  
you ask, somewhere between 5W and 100W: http://answers.yahoo.com/question/index?qid=20070907111526AAG1QF4

I'd always been told a rule of thumb that humans could produce about  
1/8th a horsepower. 1HP is about 750W, so that's pretty close.

As for alternatives to riding a bike, check out http://wiki.laptop.org/go/Cow_Power 
  - they're working on a design where you tether a cow to a long lever  
and walk the cow around in a circle pushing the lever, which is run  
through a few up-ratios to spin an alternator. I would suggest an old  
10-speed bike for the first stage, perhaps running the alternator off  
a belt looped around the rim of the 700c wheel. I expect a similar  
mechanism could work with a rope and belt or shoulder harness for  

As for dynamos versus alternators - the advantage of an alternator is  
that you can adjust the strength of the magnetic field in the rotor. A  
dynamo has fixed magnets, which means it's really only good for  
generating a specific voltage at fixed RPM.

The next step after a static exercise bike, of course, is figuring out  
how to attach a high efficiency alternator to your pushbike, storing  
the generated electricity in an accumulator of some kind (deep cycle  
lead-acid, or lithium-ion), and using that to power your laptop after  
you ride to work.

Ultimately, what you need to do is stop using electric lights, TVs and  
stereos. Just accept that it gets dark at night time, and learn to  
enjoy reading books or playing card games with your friends. The power  
you don't use is more valuable than the power you generate "for free"  
in your own backyard.

Enjoy :)

PS: There is an "airline" adaptor available for the MacBook, which has  
a connector on it that *looks* like a cigarette lighter fitting. Don't  
be fooled :)  Airplanes supply 16.6V to the connectors, while cars  
produce a maximum of about 14V. I think the MacBook can handle up to  
20V, so I'm not sure that connecting it directly to a 24V supply would  
be a good idea - though avoiding the DC -> inverter -> AC -> power  
pack -> DC conversion sounds appealing.

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