David Butcher has built a Pedal Powered Generator:
Every morning, I pedal to generate electricity. The Pedal Generator I ride charges batteries, that run an inverter, that produces 110v AC, that powers LED lights, the monitor on my computer, my cell phones, and many other small battery-powered things. It is the most inspiring workout you can imagine.I built the first version of the Pedal Generator in 1976. Let me describe my invention to you. As an improvement over similar bicycle generator designs, I went all-out for efficiency and versatility. While a bike generator is an alternative to my design, pedaling will be uncomfortable and inefficient, and powering non-electric equipment may be difficult. A key feature in my design was a 36″ particle board disk with a groove routed in the edge that served as the flywheel and crankshaft for the permanent magnet 36 volt DC motor seen at the upper right edge of the device. A small-pitch chain provided the power transfer system. The groove around the outer edge was lined with “rim strips” — thin rubber straps that prevented the chain from slipping and digging into the particle board. They are standard bicycle parts. The motor was obtained around 1985 from Northern Hydraulic, now known as Northern Tool and Equipment Company. It is a General Electric Permanent Magnet Motor, model 5BPA34NAA44, a very nice heavy-duty, ball bearing unit. I paid USD $29 for it if I remember correctly, and I still have it.
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The particle board disk was a key feature of this unit. The weight of the disk served as an excellent flywheel. Human legs and pedals create an extremely “peaky” torque curve, resulting in jerky motion and lots of stress on parts. The flywheel smoothes this all out by absorbing part of the energy on the power stroke, lowering peak torque, and releasing it on the “dead” part of the stroke, creating torque where Human legs/pedals cannot generate any. Another thing to remember is that Human legs do not like extreme stress. The flywheel allows the Human to avoid having to generate extreme pressure during the power stroke just to make it past the “dead” spots. Many “bicycle converters” lack the flywheel characteristic because tires/rims are designed to be so light.
Practical? Not really. A fit cyclist might maintain a 150-Watt pace over a half-hour, generating 75 Watt-hours — or 0.075 kilowatt-hours.
It’s most useful if you’re both off the grid and overfed, which is a rare combo.