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914World.com _ 914World Garage _ car relater but OT

Posted by: wilchek May 14 2005, 08:57 PM

I am trying to build a home generator off of a VW bug generator and a exercise bike. Ride the bike---see the light turn on, for a sciene project for kids. Does anyone know if the generator of VW bugs had "permanent magnets" or do I need to hook up a battery to the generator to develope a field current (energize the magnets). Any help would be great. Any other suggestions would help as well. I am at the trial and error part.

Posted by: scott thacher May 14 2005, 09:20 PM

yes it needs out side current for the exciter which must be connected through a resistor or bulb to ground ( IIRC) . when you apply the source power the light will come on once you start making power the light will go off.

you might do better making a generator out a small electric motor with permanate magnets

Posted by: bd1308 May 14 2005, 09:27 PM

what the hell is that good for? so the generator needs power to produce power??? isn't that counter-productive?

Posted by: bondo May 14 2005, 09:34 PM

QUOTE (bd1308 @ May 14 2005, 08:27 PM)
what the hell is that good for? so the generator needs power to produce power??? isn't that counter-productive?

You generate electricity by moving coils of wire through a magnetic field. Both alternators and generators use an electromagnet to generate the manetic field, because you can control the output by varying that field. The energy required to make the field is much less than the output, so it is only slightly counter productive. The down side is if you have no electricity to get it started, it won't generate anything.

Posted by: wilchek May 14 2005, 09:38 PM

Thanks Scott, that is what I thought

kind of, it will produce more than the battery puts out. It will produce some power without the battery hooked up. It is generally not strong enough without being an electromagnet. Your car alternator will not work without a battery. However, there are some generators/alternators that have what is called permanent magents that do not require external batteries but have less output (noramally power window motors have permanent magents). Bottom line, spin the gen/alt faster or add more magentics = more power.

Actually most voltage regulators work by adjusting power to the magnets, creating the proper amount of supply out of the alternator of around 13.5 volts.