EcoRenovator - View Single Post - Building a pedal power bicycle 12 volt generator, ghetto style

MetroMPG · 01-18-09, 07:59 PM

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.

01-18-09, 07:59 PM	#38
MetroMPG Infrequent noob Join Date: Aug 2008 Location: 1000 Islands region, Ontario, Canada Posts: 402 Thanks: 37 Thanked 20 Times in 19 Posts	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. __________________ . To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.