Bike generator for Tufts Kid's Day Fair 2008

I'm a member of engineer's without borders at Tufts, and as part of a community outreach initiative we decided to build a bike generator for Tufts yearly Kid's Day Fair.

It was excellent demonstration of energy efficiency. The kids could either power a compact fluorescent light or a set of incandescent light bulbs. The incandescent bulbs are on the handlebars and are not completely visible in the pictures I have. :-(

The generator was a 12V dc motor from Grainger. link

The incadescent lights were automobile headlight light bulbs. The compact fluorescent was a 12 V DC model typically used for RV's.

A big old capacitor (1 F) was also wired in to help regulate the voltage.

Message me if you have any questions.

Big thanks to everyone on instructables that gave me advice in making this project!

Comments

[iainlikestocook]

Fantastic bike generator! I am somewhat of a rookie here. I am curious as to how a car alternator would work because of the massive amount of RPMs I would have to produce?? I'm more so perplexed as well as to why you are using such a massive capacitor; I am planning on charging a 12V car battery, do I need an capacitor as well in order to use an alternator as the generator?

[greatboss]

very good,i like it .it is better to put on more details .

[philipster]

hey for the dc motor could you use say a generator out of a car and would it produce more energy?

[musing mumbler]

We originally planned to use a car alternator (generator) for this project. We even bought one from a junk yard, but we just couldn't get the gosh darned thing to work! They tend to be car-model specific and it is difficult to determine how to repurpose them. Car alternators are nice because they maintain a constant voltage no matter how fast they are being spun. This is good if you have things like sensitive electronics to power that you don't want to break. However they use some of the power they generate to regulate their voltage, which decreases their efficiency and power output. If you are going for more energy per time, then I would suggest a DC motor.

[bgrasmeder]

I helped work on a bicycle powered guitar amplifier and we used a car alternator. The big snag was that alternators require electric flow INTO them before they will produce anything out, so we used a battery that fed in. You also have to have a switch to engage the device only once you've got enough rotations per minute on your bike wheel. Think about your car and how it stalls below a certain RPM. You have to get it up and keep it up above that threshold RPM before you engage the system.
(http://www.gypsycarnivaltour.org/)

[magganrchy]

I had this same question and someone answered it for me so here goes. Alternators in cars have a magnet and a copper coil just like any other generator...but the magnetic isn't permanent. It takes a little bit to generate the electricity needed to turn the magnet INTO a magnet powerful enough to generate a measurable amount of electricity. (there is a small residual charge that generates the energy at the start) if you replace the magnet with Rare earth magnets then it will work just fine...or you can just pedal really hard at the start.

[luigi2999]

The reason why you couldn't get it to work, is because you have to get the alternator up to speed, then u have to energise the fields of it to make it start to produce electricity, then, once you energised them, it should work fine.

[musing mumbler]

Yep, we realized we needed to do that, but we couldn't figure out how to hook it up to a voltage source.

[luigi2999]

U mean a load? The alternator is a voltage source, and light bulbs are a load. There may be no negative terminal, the alternator casing itself may be negative, while there may be only one pin for a positive terminal. So, you may want to solder a wire to the case, and hook up a wire to the terminal, and test the output voltage with a voltmeter.

This guy shows his set-up of a car alternator and bike, check out this vid.
http://www.youtube.com/watch?v=R_-wVuEkk2E

[lordploppy]

Hola! Complete amateur here... we are thinking of putting something together that will power a television. What are our chances of generating enough power to do that?

[omnibot]

May I suggest a large stepper-motor? These can be used as very effective AC-generators but you will have to ad rectifiers. Google for "stepper motor generator".

[musing mumbler]

You could power a small TV with a bike generator if you wanted to. (link)

This design would not be good for a television. The motor we repurposed as a generator was rated for 12 volts at 2350 rpm. This means that we would only theoretically reach this voltage spinning the bike wheel 2350 times per minute. Voltage would fluctuate widely with wheel speed, and the TV would most likely be broken.

You want to look at a design that includes a car alternator (see other comments). Look at the other designs on instructables (particularly the one by bdwhaley here) and take a peek at the link above.

[wingsinger]

Nice bike generator! The Grainger link no longer works,do you have the part number for the DC motor you used? What kind of Wattage output are you getting?

[musing mumbler]

Hmm? The link seems to work for me. . . The grainger part number is 1LWK8. I'm not sure how much wattage we were getting. Powered by the typical hyperactive 10-year-old, we were able to power a 15-watt compact fluorescent light bulb and still have some juice left over to make the two incandescent bulbs burn brightly. The motor is rated for 21 watts, soooooo I'm going to guess around 18-19 watts. Not really that much, but enough to make the kids appreciate grid electricity! :-)