General Cycling Discussion - bike trainer/12v generator

For a winter project with my girl I'm thinking about building a bike trainer/power generator (got welder, metal is cheap, can pick up a small car electric generator for maybe $20, a used battery for another $20). I'm thinking something like the one outlined in http://www.pedalpowergenerator.com/, but without the moronic price tag (it tallies up to almost $1,000).

Has anybody here built one using a car generator? As a trainer, how well does that work for resistance?

Cars haven't used generators since I was a kid. They use alternators now, so that throws an extra complication in. You need more electronics to get back to DC.

I did the math long time ago, and if I remember right, you would have to pedal most of the day to get 5 cents worth of electricity.

But it sounds like an enjoyable project, and you never know where it could go.

I did the math long time ago, and if I remember right, you would have to pedal most of the day to get 5 cents worth of electricity.

A 1hr TT (assuming an FTP of 250W) would yield 0.25kWh of electricity. Assuming electricity is about $0.10/kWh, that's 2.5 cents (also assuming perfect capture and transfer of the electricity).

To make ten cents, you'd basically have to ride a century on the trainer.

I still think it's kind of cool. You could power small appliances up to a personal desktop computer. Though those obviously vary, a round figure is 250W. A laptop would be less. A line conditioner would also help a lot to keep it steady.

So probably better to think in terms of what you could power with the output vs the amount of money it's worth. With a good setup, you could make it happen.

German made tire driven bottle dynamo, AC in 12v is about $400..

I tried a alternator driven off a stationary bike at a Science museum..
you cannot work hard enough to make the kind of light as seen in the film
Soylent Green, in reality..
its hard to even make a 60w bulb glow more than orange , below incandescent,
for long.

you can increase the resistance with a greater electric load..
measured , yes, in watts.

This project is more so I can get a neat bike trainer for the winter, and my girl a working understanding of electricity. I have a super compact motherboard that runs off a 19v power brick. If i pair that off a LED monitor I may be able to generate enough watts to play a game :)

Modern car alternators indeed generate AC but they have a built-in rectifier to turn it into DC, that should not be a problem. Oldish ones even have a built in voltage regulator but those are not common. The norm nowadays is to shove that into the car ECU.

I'm just realizing how much I have forgotten. Is there a good website to relearn the basics of electricity?

Could you charge a trolling motor battery and run some LED lights for an extended peroid of time. I could use something oike that in the basement.