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Salvador

Wed Jun 10 2015, 08:58PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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Posts: 86

Hello everyone, a while ago here and also on some other places I was asking questions and talking about faraday disc etc. to cut a long story short, the main idea was that to achieve a generator whose output frequency could be independant from the rpm it has or other geometry related things the closest candidate could be a faraday disc or alike homopolar generator with few more turns , in other words if you put a field coil on the faraday disc and supply whatever AC signal to that field coil the output from the disc should be the signal +the added current and voltage from the kinetic energy transformed into electrical energy.the main thing is that the output should have the same frequency and waveform as the signal fed into the field coil.

Now the homopolar/faraday disc generator has a drawback , one part of the same current generating loop always has to rotate with respect to the other which means mechanical contacts are needed like slip rings and brushes which adds noise and losses to the system.

So here is my idea , can we have that same property but using a brushless design so the easiest way to imagine this is with a AC asynchronous induction motor's stator, and then using a solid rotor whose geometry resembles that of a solid cylinder whose two sides are cut off along the radial direction.the field coils are on the stator and also a single output coil wound evenly around the stator. the field coils are located such that both both like poles always point into the stator and other two poles have a flux path that leads into the rotor much like the flux path on a speaker magnet is diverted through the magnet hole back to the air gap.
now the rotor has two sides were the flux is high because the rotor is very close to the stator at those places and then it has two sides where it is further away from the stator so the flux is lower at those places.
as the rotor is dragged around the places where flux is high rotate also so that should cause induction into the output coil but the flux polarity and intensity through the rotor is determined by the field coils so the output should follow the singla fed into the field coils only with a higher amplitude (voltage) and curent.

I made a silly little drawing that should help top understand my idea.the arrows in it point to the parts where the flux would meet as the rotor turns around.

Electroholic

Thu Jun 11 2015, 01:12PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

Look into DFIGs.

Salvador

Thu Jun 11 2015, 09:31PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
Location:
Posts: 86

I have looked into them and read about them , but this is well atleast I believe a little different , in part because DFIG have slip rings atleast the working designs, this one doesnt.
also as I'm learning physics while thinking about these maybe someone can comment on whether something like i describe works or not.

thank you.

Uspring

Fri Jun 12 2015, 11:25AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

Think about a standard AC generator with a rotating permanent magnet surrounded by a stator of coils. That will produce an AC frequency corresponding to its rpm. You could now replace the permanent magnet by a magnet which creates an AC field, e.g. a rotor made as a coil. You will then get an AC voltage in the stator being the sum or difference of rpm and rotor field frequencies.

That would require brushes, though. Another possibility to get an AC magnetized rotor is to use a second stator, which magnetizes the iron rotor. This second stator would need to be driven by an external AC voltage. It is somewhat a headache to work out, whether this would produce more electrical power in the first stator than is fed in from the second one.

A third possibility is to use a number of permanent magnets as the second stator. You will then have an output frequency dependence on rpm again.

Salvador

Sun Jun 14 2015, 11:22AM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
Location:
Posts: 86

yes but why have all of that , here the idea ( if it works) is that you feed a certain frequency and waveform into field coils and direct the resulting flux from the poles of the field coil through the stator at one side and through the rotor at the other , the magnetic field lines will meet at the airgap but sicne of the uneven shape of the rotor the places with higher flux density will be dragged around a stator coil so that the coil has varying amount of flux changing location to make induction possible but what matters is the induced frequency and waveform which to my mind in this case should follow the one fed into the field coils , much like an amplifier follows the input signal adding current and voltage to it.

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