Building a pedal power bicycle 12 volt generator, ghetto style

[MetroMPG]

I forget, but I'll check when I get back to the apartment (at the library right now). I think it's a really easy 3-bolt removal type of job on the firewall under the hood.

If you have the option of getting a LARGER motor, I think I'd recommend it. The little Metro one works, but the lowest power output shown was at 65 pedal RPM, and ~7000 motor/generator RPM; to get the highest power output, I had to spin fast enough to be impractical (also the voltage is too high to feed a battery for a long time - I'd cook it.)

I'm planning to post a summary and "lessons learned" with a bit more detail. Also get a bit of video.

[MetroMPG]

Well, I had a look at the car, and the blower must come out from under the dash. Not sure why I thought it came out from the engine compartment. It's colder here (-15C), so I didn't hang around having a closer look at things.

[bennelson]

I have benn SOOO planning to do an exercise bike generator for a while.

I finally got my wife a nice, used, recumbent exercise bike. She really has been enjoying it so far - Which means it's time to Mod it!

I also happened to buy it for her the day before I bought the Mercedes for my bio-diesel truck conversion....

I know of a couple of people at an ecology group who seriously are interested in an exercise bike generator to run a laptop or two at their office. I figured I would experiment with mine at home to come up with a decent design, but it looks like you beat me to it!!!

[NiHaoMike]

Add a Schottky diode for an automatic disconnect.

[james]

So how did you wire it? I have heard that any motor can be a generator, but what keeps the battery from using its juice to spin the motor?

[james]

Hmm. A larger motor...I've seen a few trucks sitting around that may like to be donors for this sort of project. Maybe a chevy truck blower? Or would you recommend a different type of motor altogether? Would it be worth setting up a belt or chain drive? Thanks for going out there and checking out how hard it is to pull that blower motor. When I said 0 degrees I meant Farenheit, which might be close to -15 C. I cant do the conversion in my head.
-J

[Daox]

An alternator would probably be ideal. It regulates its own voltage and everything for charging batteries. Just make sure you have it geared right so its spinning fast enough.

[MetroMPG]

MISSION ACCOMPLISHED: Yesterday I recharged my camera's batteries with my legs.

Here are my thoughts:

Using an alternator: I'm not sure a conventional alternator would be a good choice because it can potentially output so much more power than you can generate with your legs. Depending on how aggressive the output circuit is, (eg. if it tries to output 20A to charge a low battery) you may not be able to keep up with it.

I know pedal/alternators have been done though (* but using a capacitor as a buffer instead of a battery), and it turns out I also have (back in the Ontario junk pile) just the type of alternator used in this example project: Build your own / do it yourself bike generators Pedal Power . I may give that a try later in the spring.

The biggest problem with using a 12v permanent magnet motor is the RPM it needs to spin to generate useful (> 12.6) voltage. The calculations: I need to spin the pedals at least 65 RPM to see the battery voltage start rising at a reasonable rate. 65 pedal RPM = 248 wheel RPM in top gear = an astounding 7090 RPM for the motor/generator (7/8 inch hub diameter).

More gears would be useful, if staying with a motor like this. Current config: 42 teeth front & 11 teeth rear.

Best motor/generator choice: would be a 24v or higher motor which doesn't need to be spun so fast to generate useful voltage & current.

It's kind of noisy. @ 7k+ RPM, the sound of the motor hub running on the tire, plus my chain touching my front derailleur (big ring crank sprocket bent from smacking into too many rocks), plus the spokes & tire treads churning up a breeze = a bit of a racket. I have to seriously turn up the radio if I want to listen to it while generating power.

Generating power is a lot of work! I tried recharging my laptop battery through the inverter, while the laptop was also running (listening to a podcast). I only managed to bring the battery SOC up from 86% to 92% in about 15-20 minutes, and it was more of a workout than I wanted to sustain to get the job done! I quit when the sweat started to run. (And I'm in reasonably good shape.) I think the laptop uses around 65 watts to both run and recharge at the same time. I have no idea what the various conversion losses are in this mickey mouse system, except that it was definitely way more than 65 watts worth of work.

It's also kind of fun. I've never been one to enjoy riding a stationary bike. I view it as something like taking medicine. But doing something useful while spinning the pedals is an interesting incentive that actually makes me want to get on the bike.

In fact, I got on this morning and fired some watts into the battery for 15 minutes before breakfast... um, just like Ed Begley Jr! I suspect this contraption is going to keep me more active this winter than I would have otherwise been.

[MetroMPG]

Originally Posted by NiHaoMike

Add a Schottky diode for an automatic disconnect.

Yeah, that would be ideal. If I had a ratshack in town, I'd probably do that. But I'll probably just keep using the switch I wired in. I just spin up to about 60+ pedal RPM, then flip the switch.

Originally Posted by james

So how did you wire it? I have heard that any motor can be a generator, but what keeps the battery from using its juice to spin the motor?

Simple: battery (-) to motor (-), battery (+) to motor (+) with a switch in that wire.

Yes, the battery will spin the motor and cause the bike's rear tire to spin if I simply flip the switch and don't pedal. But if I pedal faster than the motor would spin the tire, the power flow reverses and sends juice back down to the battery.

Originally Posted by james

Hmm. A larger motor...I've seen a few trucks sitting around that may like to be donors for this sort of project. Maybe a chevy truck blower?

Yup - I think that might be a bit better. Anything that spits out a little bit more current than the one I have would be good. Bigger magnets = more current (likely).

Or would you recommend a different type of motor altogether?

A permanent magnet motor from a 24v or greater application (wheelchair, disability scooter, computer tape drive) would be better, since you wouldn't have to spin it as fast to get 12v from it.

Would it be worth setting up a belt or chain drive?

Yup. If you can gear it down more with a belt or chain/extra gears, that's good. I could make the motor/generator hub smaller, but it's more likely to slip against the tire when the load goes up.

[MetroMPG]

PS - I'm still planning to capture & post a bit of video of the works in action... using my human powered camera.