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How would I build an electric generator with variable torque? It's my understanding that P=T*rpm, but that T is const. Answered

I am interested in retrofitting a spiinner bike to produce electricity. The spinner currently uses brake pads to adjust the resistance. There is plenty of energy being 'lost' in the form of heat due to the brakes. I would like to be able to adjust the resistance of the bike without losing energy in the form of heat. I understand that gears are a possibility, but I would prefer to be able to adjust the resistance in a continuous manner. Any ideas? I've considered a CVT (continuous variable transmission) design, but this would be quite difficult. I've aslo wondered if the relative motion of a disk with permanent magnets to a disk of stationary coils would vary the resistance. I'm not sure what the range of variation would be however. Any suggestions or insights you might be able to offer would be much appreciated. Thank you.



4 years ago

Hello You,

When turning generator that is not under any load, there will be nearly zero resistance. if you short out this generator there will be a great deal of resistance. When shorted out the resistance is the maximum, when no load at all is the least resistance.

There are many ways to build what you want. I will tell you of two.

ONE: get some permanent magnet generator/motor and hook it up. Use an adjustable voltage regulator to control the amount of electric going into the thing you want to power (i.e. a battery). I think this is the easiest thing to do.

TWO: Build a permanent magnet alternator as seen in hundreds of how to videos on youtube. when they say how to wire it, ignore that part, wire it so that each coil can be turned on or off. EXAMPE; you have 8 coils, each coil is connected with the ability to charge a battery (but is in the off position). Now as you pedal the bike you can switch on one coil at a time, increasing resistance with each coil. this means you will have 0-8 setting levels of resistance.

NOTE: there are many electronic details I am leaving out, you will need to do your own research (easy with google) to find out how to wire up this stuff.

Good Day!



9 years ago

hi folks,

i have found that it is possible to vary the mechanical resistance/power output levels with a standard PWM controller. you can see the details here.


kindly leave a comment at the end of the project if you find anything of use.

cheers and good luck with your build! dave


10 years ago

At the local Science Museum, there is a display made up of a bicycle generator and 3-4 appliances like a light bulb, radio, and something else. The more appliances you turn on, the harder it is to peddle the bike. So, I would say, use up the power generated.