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MetroMPG 01-14-09 08:10 PM

Building a pedal power bicycle 12 volt generator, ghetto style

I've wanted to do something like this for a while, mostly because I think it'd make for an interesting and cool project.

Use my existing bike to generate DC power to charge a battery which I can then use to power various small household AC things through an inverter.
Generally to learn stuff about this stuff. My existing level of expertise with human powered generators is ... as a kid, riding one of my neighbour's bikes with one of those generator-against-the-front-tire powered headlights.

Also, I sit on my butt most of the day. Being able to hop on the bike and feed a few watts into a battery will be a good break to get the blood flowing.

Also also, it's winter, and the apartment I'm staying in has zero insulation. I can either be completely sedentary and crank up the heat up to feel nice and warm, or I can occasionally hop on the bike for a few minutes of pedalling. :)
Haha! Budget? I don't need no stinking budget!

This will be as close to free as possible. Scrounged. Ghetto. Used parts. Stuff I've already got.
So here we go...

Edit: added January 21, 2009... YouTube video of the project's success!

MetroMPG 01-14-09 08:34 PM

Here are the parts I've got:


My "classic" GT Karakoram mountain bike. Mountain Bike Magazine "bike of the year" in 1997, woo!! Still delivering lots of mountain biking fun after 12 years. My biking friends have gone through 3 or 4 bikes apiece in the time I've owned this one. I've sworn to ride it until either (a) I snap it in half, or (b) replacement parts are no longer available. Hey, it still gets me up the same climbs it did when it was new.


This is a permanent magnet 12 volt DC heater blower motor scrounged from one of the 2 cars that were used to build the ForkenSwift electric car. It used to have one of those "squirrel cage" fans on the shaft, which I have already cut away, down to a rough plastic hub on a steel "D" shaped shaft.

I don't know the motor's rating, but I'm guessing it could pull about 5 ish amps continous in its life as a blower motor. If I can get it to output 5A, that would be a useful amount of current for charging a battery.

Battery (12 volt):

Don't actually have one yet.

I figured I'm probably just going to go around to the local garages/parts stores and see if someone will give me one that's recently been swapped out. If I can find one that'll take a 12v charge, that's good enough. I'm not looking for tons of capacity.

DC/AC inverter:

I've got one pretty much exactly like this one. 150 watts peak AC output. Good enough to run a laptop, clock radio, or a small fluorescent lamp.


Just a regular inexpensive digital multimeter, with a 10 A current function as well. So I can monitor how much voltage & current I'm stuffing into the battery and how much I'm draining it down when basking in the power being used to run my vast collection of fun & useful consumer electronics!

Up next: plan of attack...

MetroMPG 01-14-09 08:36 PM

Here's the plan, such as it is:

Step 1: make a stand for the bike

Step 2: attach the motor to the stand so it spins off the rear tire somehow

Step 3: pedal like crazy, and hook the motor wires to the battery when the RPM/voltage is high enough to feed juice to the battery (rather than have the battery spin the motor). Generate lots of "free" power.

Step 4: Reap the fruits of better living through physics and chemistry! Or something.

Today I did step 1, and ended up with this:

Ghetto bike stand made out of scrap wood!

I was going to use a discarded shipping pallet for the wood, but found some other scraps, so I didn't have to spend time disassembling a pallet. Yay.

I've already test ridden it. Functional & stable! Next time, I'll post how I put it together. Though it's obviously tailored for this specific bike, you could probably adapt the approach for any bike.

SVOboy 01-14-09 10:21 PM

Don't you have a trainer you can use?

Daox 01-15-09 05:53 AM

Woooo, its prettier than I had imagined. :) What are your current thoughts for mounting the motor so it touches the tire?

MetroMPG 01-15-09 07:17 AM


Originally Posted by SVOboy (Post 1709)
Don't you have a trainer you can use?

Trainer? No sir! I'm not training for anything.


Originally Posted by Daox (Post 1710)
Woooo, its prettier than I had imagined. :) What are your current thoughts for mounting the motor so it touches the tire?

More wood! More screws!

The good thing about the motor is the big flange attached to it, so it shouldn't be too hard to mount on some wood. I think I'm going to extend one of the bike stand uprights and mount the motor on the top of the tire.

My engineering challenge is: this is a knobby tire, so while orienting the motor to run against against the tread face will be easiest, it'll also be pretty bumpy and kind of noisy. Running the motor against the side of the tire would be best for noise & good contact. I should probably design it that way...

Doofus McFancypants 01-15-09 07:32 AM

Cool idea.

as this is for generaton purposes - maybe you can find a scrap 10 speed real wheel and fit it on there with a "slick" tire.
take your bike - swap the rear wheel for the "slick" to genorate.
when you go MTbiking - swap them back.

no damage to your Off road wheel

PLus, then you could mount the generator it as best fits on the frame / wheel


Daox 01-15-09 07:41 AM

1 Attachment(s)
I was thinking about this and thought I'd share my thought on how to mount the motor to the side of the wheel. Its not too complex and shouldn't be too horribly hard to make. Here is a real rough picture of it.

MetroMPG 01-15-09 07:48 AM

Good idea, Doofus, I'll keep my eye open. Being wood construction, it'll be relatively easy to mod if something turns up.

Let's call this version 1.0.

If it works, I'd consider using some scrap bikes when I get back to Ontario in the spring to make a dedicated (non-rideable) compact version.

Thanks for the diagram Tim. Now I have to buy a hinge! There goes the budget! :D

MetroMPG 01-15-09 07:51 AM

Over at, someone commented...


Check "Livin' with Ed" on the Green channel.. he does this every morning to make his toast... 15 mins on the bike.

I don't know if the blower motor will be the most efficient source of energy... I'd think using a car's alternator might yield you better results.
Yeah, I've seen Ed makin' his breakfast before. On "Cool Fuel Roadtrip" I think.

I'm under the impression that the perm magnet motor is a bit more efficient than a car alternator. According to Wikipedia, a modern alternator is only between 50-62% efficient. Though the output of the alternator can be much more than this motor.

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