Learned ones: I posted this request to another (non-usenet) forum and was referred to you by a friend in that forum. I did also cross-post this in alt.energy.homepower, at his suggestion. When I posted there, I discovered that I am using a usenet account established by my nephew several years ago. The account is his name (Brian Wood); my name is Dennis McKim and I live in western Colorado. Sorry for any confusion that causes...
It is difficult to present my current 'daydream' in a reasonably short post, but allow me to try: I plan to purchase a recumbent tadpole-design tricycle (see
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for photos). "Chain management" is often an issue for recumbent trikes, and idler pulleys are often used to control the chain as it passes under the seat. I enjoy riding before sunrise and after sundown, and will need reasonably powerful lights on my trike. I plan to install a 14.8 volt Li-Ion battery pack, with a (nominal) 12 V lighting system (HID or multi-LED headlamp and tail lamp, and a 360° amber strobe light mounted on a pole behind the seat). I wish to consider a small 12 V generator driven by a toothed idler pulley, mounted low behind the seat. It will serve for chain management and power generation. My front chainring will be 32-tooth and the rear gearing will be an internal hub, so the chain velocity will be constant (no rear derailleur). My normal pedaling cadence is 80 RPM, so the 16-tooth idler pulley will be driven at ~160 RPM. I need an output of only 3-4 amperes, and might get by with only 2-3 amps. I don't need to power all of my lighting exclusively from the generator; I need to keep the battery charged and then extend its run-down time after dark when I turn on all the lights.***** Is it feasible to try to construct a generator, using rare-earth magnets and copper wire, that will generate 15-18 volts, and have a package something close to the size of a can of soda pop (2-2½" diameter, 4-5" long)?
***** My research to date finds many designs for homemade generators, but all of them are large diameter (6-10 inches). That is great for wind turbine projects but not suitable for my dream. I've heard of using brushless DC motors as generators, but all that I can find operate at very high RPM. There are dynamo hubs available for bicycles, but they all generate 6 volts and I am committed to a 12 V system. There are "bottle type" generators for bicycles that drive against the lateral surface of the rubber tire, but I am (at least for now) set on designing something driven from an idler pulley. What do y'all think? Totally feasible? Impossible? Somewhere in between? Just to keep the discussion on track, please understand that I am also investigating the options of solar power to charge the battery, and of using a larger battery and "home-charging" it. My purpose for posting here is only to inquire about the technical feasibility of constructing a (very) small
12V generator being spun at only 160 RPM. Thanks in advance, Dennis