# Generator output frequency and rpm

jim hardy
Gold Member
2019 Award
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hmmm i thought the eddy currents in a homopolar machine flow in the plane of the disk....

can you re- state the question about rotating transformer? That's one way to think of induction motors, hence my suggestion to look at the "double fed induction" machine..

ok the question one more time , if i had a homopolar (faraday ) disc which uses a AC magnetic field instead of a DC one , could I use a rotary transformer to collect the generated current instead of slip rings or brushes ,I somehow assume this doenst work because the faraday disc was unique in a way that it required that there are two parts of the same generating loop but one is rotating while the otherone isn't?
or maybe once can overcome this by slicing the disc(loop) in many smaller portions like a pizza and then each portion passes by a magnet and a collecter transformer at the same time but then it wouldnt be a true homopolar machine anymore I guess rather a weird induction machine.

A unipolar machine relies on the Lorentz force similar to the Hall effect. A time varying magnetic field (what you call an AC field) machine relies on Faraday's law of induction.

Thus a unipolar machine relies on the physically changing position of the electrons while the AC machines uses the time changing magnetic field. So yes, you could build a machine the way you suggest. You could make it better by making the pizza slices into thin cylinders (wire) and wrapping them around iron cores in both the rotors and the stators. You could use one of several well known configurations.

However you could also probably come up with your own AC motor with a higher current capacity (at a cost in both voltage and efficiency) than a typical machine by using the principle of low resistance found in the Faraday Disc.

But it sounds like an invention looking for an application to me. If you already have the application, good luck.

ok but the question is is a homopolar , unipolar (whatever you call it) machine works on a AC field isn't there two processes now at work , both the induction from an AC (time varying) field and also the lorentz drag as in an oridnary homopolar machine , because an AC field at any given instant in time is also a DC field so it still exerts force on charged particles, just that the force reverses according to the field and also the amount of force changes in each direction as the field builds up and then falls off.?

thanks for the answer Jeff, but the even more interesing part I was hoping to hear about is whether you can still have a true homopolar machine but without brushes or slip rings when you use an AC field ? ignoring efficiency , or anything else just pure physics would a faraday disc spun in an AC magnetic field be capable of outputting current via a rotating transformer of which one part is mounted on te spinning disc and the other part is stationary?

?