Gary Neal wrote: > I've got an old 3-phase 230/460V, 3/4hp electric motor that I was thinking > about using for a generator (maybe as part of a windmill). > > Here's all the details I know: > > 9 lead wires > Seems to be a wye configuration > When spinning the shaft at 900rpm, get ~10V line-line on the outputs > The Rotor has no wire connections or slip rings or anything. Just a bunch > of laminated plates that spin on bearings (not magnetic) > Rated speed is something like 1170rpm > Really very basic motor > > So, I've got a couple questions: > > 1. What "type" of motor is this? It's sad to say, but I went through an > entire Mechanical Engineering curriculum, and they taught us all about the > "theory" of electric motors, but never taught us how to identify the darn > things. Is it induction, synchronous, ...? How does it work? I'm no expert, but here goes anyway: With no connections to the rotor, it would have to be either a permanent magnet (unlikely) or an induction motor (very likely), possibly a "squirrel-cage" type if it has copper paths embedded in the rotor. > 2. If I end up using it in a windmill, I'd like to run it at low speeds > (couple hundred rpm) and charge a 12V battery. Is there an easy way to get > higher V/rpm? Not without rewinding it. > 3. I've seen discussions about needing to have "running" capacitors or be > hooked to the grid and then spin the motor slightly faster than its rated > speed to generate electricity. This was all over my head and I was getting > disappointed until I just took a couple LEDs and hooked them across the > leads, spun the shaft, taaadaaaa, they lit up = electricity out. So, > what's the deal with that? You're probably seeing a weak generator effect arising from residual magentism on the rotor. See this web page about using it as an AC generator: http://www.qsl.net/ns8o/Induction_Generator.html I doubt you'll get much output at low RPM; I think you'll need to run it at slightly over its synchronous rate to generate 230/460V and use a conventional battery charger to charge your battery from that. At low RPM, you'd need some really huge capacitors to generate the necessary phase shift to keep the rotor energized. I think you'll be happier just using a regular car alternator in your windmill and using this motor elsewhere -- perhaps as a gasoline-powered backup generator. -- Dave Tweed -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads