Building a pedal power bicycle 12 volt generator, ghetto style
 

http://ecomodder.com/imgs/bikepowerplant.jpg


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

Goal:

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.

Motivation:

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. :)

Budget:

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!

http://www.youtube.com/watch?v=tzQiurfsypI

Here are the parts I've got:

Bike:

http://ecomodder.com/imgs/karakoram-roof.jpg

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.

Motor/generator:

http://ecomodder.com/imgs/motor-blower.jpg

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):

http://tbn1.google.com/images?q=tbn:...07/Battery.png

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:

http://www.all-battery.com/ProductIm...W_Inverter.jpg

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.

Instrumentation:

http://www.cbtplanet.com/images/multimeter.jpg

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...

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:

http://ecomodder.com/imgs/bike-stand.jpg

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.

Don't you have a trainer you can use?

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

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

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...

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

Steve

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.

http://ecorenovator.org/forum/attach...1&d=1232026846

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

Over at EcoModder.com, someone commented...

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.

Am I going to melt this little motor/generator?
 

A couple of people have expressed doubt about the suitability of my little motor/generator. I have to admit, I decided to use it based on a W.A.G. of its specs. Am I'm going to burn it out?

I just tested the blower in my car (it's the same size motor I pulled from the older - same - car). On the highest setting, it pulled 9.1 amps @ 12.5 volts or 113.75 watts (car not running).

That's great, since that must be its continuous "rating".

How does that measure against the amount of power I can transmit through it? Well, based solely on remembering the readouts on the stationary bikes at the Y, 100 watts is a light-moderate amount of effort. Sustain that long enough and you'll break a sweat.

Of course it's possible to put out peaks of much more than 100w, but I'm not going to be riding this thing for long periods or doing sprints on it.

So I'm thinking it's going to be just fine.

cool idea!

heres a thought though. belt drive. take the tire off the rim, and run a belt to the motor. the shape of the rim should keep the belt in place. an old v-belt (or maybe even a serpentine) should work.

i once took the cover off my elliptical machine to see how it worked. resistance was increased by tightening a belt around the "wheel" in the back. now you got me thinking........

That's funny: I took apart my dad's exercise bike over Christmas. (Was mulling over this project, and wanted to see how it worked.) Same deal with the friction belt on what amounted to a chain-driven flywheel.

The belt/rim idea works, but then it complicates using the bike as a bike if I have to keep re&re'ing the tire. That's where Doofus' idea of finding another rim would be good.

Great idea, metrompg. We need one of these because we are off the grid, and have to use a generator from time to time this time of year. I would love to make one that is belt driven. I had a light that hooked up to the wheel of a bicycle when I lived in B.C. and I found that it sapped an amazing amount of power. you should use it to charge the battery in your metro and then run alternatorless.

Hey James - off the grid! Nice. You should post up your details.

You're right: it's not going to make a lot of power. Even if I can squeeze 10 amps @ 14 volts out of it (the output of a common car battery charger), it would take forever to completely charge a car battery. Which means I'll only be putting light loads on that battery.

If I ran my laptop from it all day (it pulls about 25 watts, and it's in use for about 10 hours a day on average), I'd then have to ride the bike for about two or 3 hours to replace that energy.

Here's how I made the bike stand
 

I wanted the uprights to contact the frame at two points on each side: lower chain stays, and the seat stays.

So I started by putting the bike on a sheet of paper and laying the boards against the bike to find the right width/angles at the base, which I traced out. As a result, the uprights have both negative toe-in and negative camber, to use some car terms:

http://ecomodder.com/imgs/stand-trace-base.jpg

To keep the thing from collapsing over sideways, I needed to buttress the uprights from the wide base. Triangulate! I checked to see how high I could attach the brace with some string (to make sure my heel cleared it when pedaling):

http://ecomodder.com/imgs/stand-check-tri-clearance.jpg

The chainstays rest in these cradles attached to the inside of the uprights:

http://ecomodder.com/imgs/stand-chainstay-cradles.jpg

Here's the finished stand, from above. Fore/aft stability is provided by that piece screwed to the base that runs underneath and inline with the tire. You can also really see the "toe-in" adjustment in this pic:

http://ecomodder.com/imgs/stand-above.jpg

It's not quite as strong in the "fore / aft" plane - no triangulation. But it doesn't feel like it needs it. I can add something if need be (I'd like to watch someone else riding it).

And from the rear:

http://ecomodder.com/imgs/stand-rear.jpg

Whole thing took a couple of hours tops, to make, and seems to support the bike solidly with the rear tire about 2 cm off the base.

http://ecomodder.com/imgs/bike-stand.jpg

Attached the motor to the stand...
 

I liked Tim's drawing, so I basically did what he suggested:

http://ecorenovator.org/forum/attach...ratorstand.jpg

Truth be told, I hadn't considered the idea of the hinge. But it's really useful for 2 reasons:

1) can easily swing the motor away from the stand and down to lift the bike out when it's time to be a bicycle again.

and, 2) the pivot means I can adjust the pressure against the tire via the bungee cord:

http://ecomodder.com/imgs/stand-motor-side-front.jpg

And here's the view of the motor hub contacting the smooth side of the tire:

http://ecomodder.com/imgs/stand-motor-looking-aft.jpg

And... it works! And... I already busted something!
 

So I couldn't resist. I figured I'd give it a try since I happened to have a one of those million candlepower rechargeable 6v flashlights sitting right beside me. Popped the bulb out, hooked it up and presto! A million candles courtesy of my legs.

Funny: I could see the light pulse on each down stroke of the pedal. I'll have to wear my bike shoes and clip in if I want to apply smooth power all the way around. :)

So then I hooked up the voltmeter to see how much the physical effort corresponded to the output. And then it immediately became a game of "what voltage corresponds to what amount of light output", which immediately became a game of "I guess 8v is too much voltage for a 6v bulb". Oops.

It was funny though: when the bulb expired, the pedal effort immediately became easier. But powering the light certainly wasn't "hard". I wish I could have taken a current reading to know how many watts I was pushing before it blew up.

Next steps:

Commence the junk car battery hunt tomorrow!

I laughed at that part. Haha, who woulda thunk?

I think its really cool you could feel the difference with even that small amount of load vs no load.

Yeah I couldnt believe how much the light I had on my bike slowed the bike down. And thats just a flashlight bulb! Really makes you think about how much energy is being used to power the typical house. You would need a team of cyclists riding 24-7 to keep it running.
Where should I post the info on my off the grid system?

too bad you are not nearby, I have many semi-operational batteries around here.

James, feel free to introduce yourself in the introductions forum. If you have any ongoing projects post em in the projects and improvements section. We'd love to hear about what you're working on weather it be the solar setup, ways to conserve or whatever.

That's pretty cool. I'm pretty sure my 6 volt 1 million CP bulb says it's supposedly 55 watts on the base of the bulb. We could use Ohm's law to estimate the current if you know the voltage just before it blew (assuming the bulb really uses 55 watts at 6 volts). 55 watts at 6volts is 9.2 amps. That puts the bulb resistance around .65 ohms. So at 8 volts it was drawing around 12 amps. That puts power levels just under 100 watts.

I just remembered that I used my spotlight to load test my pv panels while they were still 6 volt output. I think the bulb ended up being a much lower load than the stated 55 watts, but don't remember how much lower. So the calculations may be a bit generous :).

I never thought of checking the bulb: so I just did, and it says 25w.

It blew out at 8v, which works out to 3.1 amps.

Thanks! But... I just got one:

http://ecomodder.com/imgs/battery.jpg

Man, I love this town. So friendly.

Second garage I went to had a pile of batteries in the corner. The owner was happy to let me pick one out (quick voltmeter auditions) after I told him what I was doing. He seemed interested.

Found one that read 12.3v, and figured that'd likely do. He said it probably just needs charging, and that people occasionally came in and insisted on a new battery, even though they didn't really need one. He even insisted on putting it on his load/capacity tester before I left. (It rated around the "50%" mark, but it's only 50% charged, so I don't know how that affects the test).

And it's less than 2 years old! Probably in better shape than my car's battery.

I paid him the scrap value ($10), which he said he'd give back if/when I return it.

Don't sell yourself short :).
The wattage of a fixed resistance like a bulb, isn't constant when voltage changes.

If it's 25w at 6 volts, that means It draws 4.2 amps (25w/6v) at 6v, so the resistance is around 1.4 ohms (6v/4.2A). Use this resistance to find the current at 8 volts. It comes out to 5.7 amps (8v/1.4ohms), so it ends up being around 45w at 8 volts (8v x 5.7). :)

I really like this project :thumbup:. It's made from stuff most people would have lying around. Wood is my favorite prototype medium :D, and it sounds like it is turning out some useful power.

Jamie - thanks for schooling me on the basics. You'd think by now I'd know a bit more than I do, eh? :)

I agree the wood is a super quick way to get an idea off the ground.

Well, it works! (Again. This time @ 12v)

It puts out a little less juice than I was expecting/hoping, but here's what I'm seeing while pedaling, connected straight to the 12v battery (which had a starting voltage of about 12.33).

Total "system" voltage on the left, amps on the right..... fast, faster, fastest:

http://ecomodder.com/imgs/multimeter-readings.jpg

Thats awesome that it works. I am going to have to do this here. How much trouble is it to take the blower fan out of a metro? My friends have one sitting in the yard, but its 0 degrees outside, and I'd rather wait till it warms up, especially if it takes more than a few mins.

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.

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. :)

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....:rolleyes:

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!!!

Add a Schottky diode for an automatic disconnect.

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?

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

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.

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.

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.

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.

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).

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.

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.

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