only a DC permenant magnet motor/generator will develop a varying voltage with varying speed. an alternator will vary the frequency which will complicate things. since you will have to use DC you should use automotive lighting devices. CFL's CANNOT deal with varying voltage nor can they deal with DC. so CFL's are not even open for discussion. An automotive Alternator with it's built in voltage regulator feeding an inverter to generate AC will allow you to use LEDs and/or Incandescent bulbs and or CFL's and the power required to power them will vary the difficulty in pedalling the bike.

but an alternator won't vary in voltage, so the lights won't dim and brighten as he cranks.

What powers the alternator's field windings at the outset?

you have to have at least a small 12V battery in the circuit to excite the field winding. once the generator is up and running the battery no longer needs to be in the circuit.

Yes.

The one working model that I am going from did not have a 12v battery. I think it had an inverter but I'm not sure. It also had multiple lights of each kind. There were 3 or 4 LED's that would like up easily, the 3 or 4 CFL's took more work, and the 3 or 4 incandescents were nearly impossible to peddle fast enough. I do want something that will vary brightness based on how fast the person peddles.

Peddle = sell.

Pedal = power a bike.

--Ed. C.

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Roroschach; for a bicycle generator why not use perment magnets, the hell with a 12 volt battery kiss keep it simple s; perry

I did say earlier that a permenant magnet generator was a possibility, but the problem is that they aren't exactly thick on the ground. they are not all that common on the surplus circuit.

Rorschach; your are wrong , a fixed voltage on the rotor will increase the output voltage as the speed increases, and also the frequency; perry

since most automotive alternators have a built in voltage regulator that adjusts the field winding voltage in order to maintain output voltage, no, I'm not.

I will say that they DO make CFL's that are dimmable, but they are expensive and hard to find.

You could buy a cheap off the shelf generator like this and go from there.

that won't work - I need it to power incandescent, cfl and led bulbs.

12VDC CFLs:

http://www.google.com/search?q=12vdc+Compact+Fluorescent+Lamps

You can probably find them (and 12v incandescents) locally from a RV or boating accessories store.

Use an inverter, but please be aware that these expect a fairly narrow range of input voltages; typically in the (automotive) 11.5-14.3 Volt DC range. Lots of places sell them now at very reasonable prices.

You may also wish to charge a small 12V auto battery through a diode by means of the generator, taking advantage of the battery chemistry as a kind of quick-and-dirty 'voltage regulator.' The diode will prevent the battery from discharging back through the generator, driving it as a motor. Make sure the battery is charged to at least the inverter's minimum acceptable input voltage. If you start out with a dead battery, your human power source(s) are guaranteed a good workout!

Use an inverter rated in excess of the largest load you expect to connect. I'd make it twice as large as that so that you don't risk damaging the inverter through operating it too close to its max rating.

A DC, permanent-magnet treadmill motor works well - if you can find a junk treadmill. If you're in the States look on Craigslist (www.craigslist.org) in your area for deals. We built a bicycle generator at uni using one of these motors. Ours powered a small TV set, as part of the project. Wanna watch those soaps? Get peddling!

Don't be the least bit surprised at how little power a Human Being can actually generate. Running that TV was work! If your test subject is in excellent condition, he or she may be able to sustain a quarter horsepower for two or three minutes. Given that one full HP is equivalent to 745 Watts, you do the math. Not much in the way of juice, is there? Certainly will give your students a better appreciation for horses...

A neat generator for a stationary bike would be to epoxy magnets to the rim, and make a coil to mount on the frame to generate the current. It would teach a lot about getting the polarity of the magnets correct, and how different windings work.

You may even be able to demonstrate regenerative braking, and switching the setup to motor by applying power to the coil.

I'm not sure if this is an alternator or a generator, it's a brushless setup.

I had one dynamo like that in my bike when I was a kid.

If I pedaled hard enough, I could make the front light work enough to see the road at night. The front light had a small lantern bulb and needed two D size batteries; I connected the dynamo to the battery terminals in the lamp and save a little fortune on batteries!

What about the Safety Factor?

Shouldn't you stay DC as a safety? or at least below 50VAC....

Us grown ups understand, kids may not and they do like touching things that can harm them.

I would hope that your class has been given a background in Ohms and Watts laws. A little transformer theory would also be appropriate as would a study on conversion of AC to DC by use of rectification.

The old bicycle generators were regulated at 3 V by the use of a centrifugal weight mechanism that would slide the permanent magnet armature out of the field as the RPM increased.

Determining the efficiency of an electric lamp is not as simple an effort as you might think primarily because the luminance is normally projected in some preferred direction, making it difficult to determine exactly how much is actually being emitted. To make this measurement accurately requires the use of an integrating sphere.

The washing machine motor is probably a constant speed 115V induction motor of less than 1/2 HP, (invented by Tesla by the way). It will not work as a generator or alternator and may be a little bit feeble to drive an auto generator or inverter which normally require several horsepower. However since you are only trying to light lamps it might work for that application. By removing the diodes it will become the alternator for which it is named, and by supplying the field current from an external controllable source will give some interesting outputs. An oscilloscope will be appropriate for monitoring the output. To control the DC output of the original alternator (the original one which has been converted into a generator by the diodes) requires a 12V auto battery in addition to the built in voltage regulator.

I'm not sure what a Convertor will do for the project, other than it will generate 120V AC from 12VDC. I might suggest that a variable autotransformer will give you any voltage you want up to about 140VAC.