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Salvador

Fri Jun 19 2015, 04:00PM

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

Hi I wanted to ask a question, I have a picture attached , a crude one but I hope you will be able to understand the idea behind it.
the overall question here is , whether it would work the way I will describe or not?

So the stator is wound in a toroidal way like toroidal transformers, it has one coil or winding on it which is the output coil, at the sides the stator material goes out to form rectangular cubes or circles on each of which a field coil wound be wound , the field coil at each side is wound in such a way so that the same poles on both sides would face inwards , the other two alike poles face outwards from the stator and are carried by an endplate (red arrow in the drawing) to the rotor, the idea is that at any given half period of AC one pole would face into the stator while the other would go through the rotor to enter the stator via the airgap.so the flux meets at the airgap at two places where the rotor is the closest , now as the rotor rotates the high flux density areas are being dragged around with the rotor, but the flux through the rotor is induced by the field coils ,

the question is would the output frequency and waveform reseble that of the current fed into the field coils or not ?
the very idea is that the conditions for induction are satisfied because of the changing flux density location , but since there is only one coil and no poles but rather just a changing flux the induced output current shoudl resemble the magnetic field that induced it and the field resembles the current that created it which is the current that went into the field coils.
in other words frequency and waveform being independatn of rpm , resembling an amplifier, rather than a typical generator.

what do you think?

Salvador

Fri Jun 19 2015, 04:02PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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P.S. I apolgize for another thread as I only now remembered that I had created one similar to this , anyways it has a better drawing so maybe you can keep it, thanks.

Ash Small

Fri Jun 19 2015, 05:48PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

A car alternator works in a similar fashion, with the rotor coil being energized sufficiently for the output from the stator coils to match the load (approximately).

Could your question be answered by feeding AC into the rotor of a car alternator, spinning it, and seeing what output you get from the stator coils?

Salvador

Fri Jun 19 2015, 06:17PM

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

i guess normally the alternator feeds dc into the rotor then poles spin past stator coils inducing current of frequency that varies with the rpm of the rotor which is then rectified , + the feedback tells how strong the dc into the rotor needs to be to match for need and rpm correct?
i guess it's called the voltage regulator or something like that.

well maybe i could try your idea Ash, but I assume the alternator still has more than one pole on the stator , by pole I mean coils, and also if remember correctly frokm last time seeing one the rotor was shaped like triangles coming from each end where each pole is located so taht makes the rotor with many poles like one after another like N-S-N-S-N and so on so i guess ti would work then , because here the idea is to maintain the frequency and waveform from the small signal that goes into the field coil to the large magnified output , and the only way I see that being done is to have one coil and a rotor that is similar to those in reluctance motors where it provides just the magnetic flux path , all other opnes have poles located on the rotor.

I dont know what do you think?

i seacrhed google and looks like all alternator rotors are pretty much the same having multiple N-S poles one after another so technically it's different from an oridnary generator which cannot produce an output based on input but rather based on the rpm of it's rotor that determine the frequency.

Ash Small

Fri Jun 19 2015, 07:55PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Salvador wrote ...

i guess normally the alternator feeds dc into the rotor then poles spin past stator coils inducing current of frequency that varies with the rpm of the rotor which is then rectified , + the feedback tells how strong the dc into the rotor needs to be to match for need and rpm correct?
i guess it's called the voltage regulator or something like that.

Yes, that's pretty much the case.

Salvador wrote ...

I dont know what do you think?

I'm not quite sure what you are trying to do. If you feed the AC in at the correct frequency, I think you might re-invent the synchronous motor

(you'd need to apply a voltage to the stator windings as well)

EDIT: Actually, I think you'd probably end up with one AC signal superimposed on top of another one.

radiotech

Sat Jun 20 2015, 07:55AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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You might want to look at the Amplidyne. It is amplifying generator.

There is a good description here.

Salvador

Sat Jun 20 2015, 09:21AM

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

I have looked at amplidyes before their interesting.Well I;m kinda tired I have talked ideas like these with multiple people on internet and rarely if anyone seems to understand what I'm trying to do even to the point where one could give me a feedback of whether it works or not.

the idea here is simple , a generator whose output frequency and also waveform to an extent resembles the input taht was fed into the field coils.seems like would be a handy thing to me atleast, one could amke smaller generators for the same output power especially where low rpm applications are used.

you are correct ash in saying that even if the rotor doesnt rotate it would still wrks as a very crappy tranbsformer since the way it is built, maybe you can explain the bit about the synchronous motor reinvention more indebt? would it function as a brushless motor also ? could it be fed with DC?

in one other forums where I asked this very question one guy is trying to tell me that the flux would produce cancelling currents in the stator coil and almoust no output would be produced but I don;'t think thats true because at any given moment only one pole goes through the rotor in other words at any given moment the flux through the rotor point only in one direction the other pole is the stator so i think this reasoning is correct ?

Ash Small

Sat Jun 20 2015, 12:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Salvador wrote ...

you are correct ash in saying that even if the rotor doesnt rotate it would still wrks as a very crappy tranbsformer since the way it is built, maybe you can explain the bit about the synchronous motor reinvention more indebt? would it function as a brushless motor also ? could it be fed with DC?

It has brushes, so can't really be called 'brushless', although the brushes aren't configured as they are on a conventional 'brushed' motor. These alternators have 'slip rings' rather than 'commutators', so they don't perform the 'switching action' that a commutator does. You would need a driver circuit like a conventional 'BLDC' motor (It 'should' spin even if you just feed it AC, but you'd need to energise the stator windings.) It would probably make more sense to drive the stator coils like a three phase BLDC and just feed DC to the rotor. The rotor would then act like the permanent magnets do on the rotor of a conventional BLDC motor.

Salvador

Sat Jun 20 2015, 01:05PM

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

Oh maybe I didn't explain every bit the way I should have. The very drawing I attached or my idea whatever you call it is a brushless design.
everything is like pictured in the drawing except the red arrows show not the path for electrical wiring or connections but the magnetic flux path as there would be something similar to an " endplate" that would take the flux from the outer poles of the field coils and provide a path for the flux to go through the rotor so that it could then reach the airgap and go back into the stator where the other pole is located.

as the rotor would turn these areas of high magnetic flux would be dragged along the stator coil and should induce current whose frequency and waveform should follow that which was fed into the field coils.

I would really like to hear whether this could work like that as the only other option I have right now is to take an old asychronous AC induction motor rewind the stator the way I ahve shown here and then cut the two sides off from the squirrel cage rotor to make it resemble this kind of rotor and then feed it with the flux the way i have shown and see what happens but thats quite a lot of work to be done so i thought to ask first for some opinions.

Ash Small

Sat Jun 20 2015, 01:15PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Can't you knock up something really basic using a toroidal core and some magnets (or simple electromagnets)?

You'd only need a couple of simple bearings and some offcuts of wood, or something (and a few other odds and ends)

You'll only need a 'measurable voltage', and any old oscilloscope will do.

You could use a small mains transformer for the AC signal, maybe, or generate it some other way.

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