Transfer of AC through rotating capacitor

  • Thread starter Salvador
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  • #26
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Why you think it's too high even for inductive coupling?
I read that many modern generators use a rotor divided in two parts, one part is is the induction part that induces current in the rotor windings so that the current traveling at the other side of the rotor to the main field windings then makes a em field which then induces current in the stator windings, some of the induced current in the statopr windings is fed back to the windings that induce the current in the rotor etc.
And the power levels there are in the order of kilowatts I believe, for comercial high power stuff.
 
  • #27
sophiecentaur
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Well then I guess if using high frequency inductive coupling is better since I get no wearing parts except the shaft bearings.

I guess theres nothing else one can do about this situation except a comutator/slip rings or em induction.
You really should not be over concerned about "wearing parts". Bigger Boys machinery than yours gets along fine with slip rings and you could go down the road to buy the right size brushes and get the rings fitted and turned by any competent operative. Design parameters for all sorts of currents and powers are all well known. Otoh, you might not know about the possible problems with your proposed ideas until the device had been been running for hundreds of hours - and then you would have a serious re-engineering problem on your hands and -down to the shop for some brushes etc.
You might find it interesting to buy a few ceramic disc capacitors (they only cost pence) and break them apart to look at the construction materials and the internal dimensions.
 
  • #28
NascentOxygen
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I'd like to hear what you are gong to do with this power once you have transferred it to the shaft. Perhaps there are economies could be made there. Maybe you don't need continuous high power?

If you have access to the end of the shaft there might be an off the shelf machine with its own bearings that could be coupled to serve as a rotating transformer.
 
  • #29
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once the necessary power is coupled to the rotor it is now in the form of current with a fixed voltage and it flows through a set os windings , few amp turns but the amount of turns depending on the frequency etc factors.
So basically its there to set up a magnetic field that would both change as the current reverses and rotate around with the rotor.
 
  • #30
sophiecentaur
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Sorry but that means absolutely nothing to me. It really is time for a proper diagram, I think. That post suggests that a simple permanent magnet, stuck on the rotating shaft, would do the job perfectly well.
 
  • #31
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Yes Sophie , it would do the job as you said. But in a faraday disc no current is induced if the disc just spins in a uniform b field alone by itself , or if the load (windings in my case) spins at the exact same rpm as the disc itself , current is only induced when the load spins with a different speed with respect to the disc or is stationary with respect to the disc.So if I dont use any brushes i need the rotor to have windings in which current flows so a b fields it set up so that once spun it woulc create a flux and current into my stator windings. Correct me if I'm wrong but a permanent magnet won't induce flux in my described situation.

Sophie , by the way , I have noticed that you have disabled PM's , is there any possibility for me to contact you to ask a few things in a more private level, guess an email would be great. If you agree you can PM.
 
  • #32
sophiecentaur
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Yes Sophie , it would do the job as you said. But in a faraday disc no current is induced if the disc just spins in a uniform b field alone by itself , or if the load (windings in my case) spins at the exact same rpm as the disc itself , current is only induced when the load spins with a different speed with respect to the disc or is stationary with respect to the disc.So if I dont use any brushes i need the rotor to have windings in which current flows so a b fields it set up so that once spun it woulc create a flux and current into my stator windings. Correct me if I'm wrong but a permanent magnet won't induce flux in my described situation.

Sophie , by the way , I have noticed that you have disabled PM's , is there any possibility for me to contact you to ask a few things in a more private level, guess an email would be great. If you agree you can PM.
This still means nothing to me, I'm afraid. If all you need to do is to find the rotation rate of a shaft, a permanent magnet will do fine, in conjunction with a single stator winding. Where does the Faraday Disc come into this? If you want a contactless way to measure the speed, how about an optical encoder?
I don't think this can progress until you state the actual problem and not just some vague ideas that you are having about a problem (possibly a thought exercise) you want to solve.

Sorry. I don't do PMs. It can all be done in open Forum afaiac.
 
  • #33
NascentOxygen
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I seem to be missing some germane posts in this conversation. Didn't this start out as how to get some kW of power onto the shaft of a motor for some ancilliary purpose? So how did the objective suddenly morph into merely measuring the shaft's RPM??

What caused this to change? More to the point---what is the precise objective at this juncture?
 
  • #34
sophiecentaur
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I agree. I suspect some wide ranging thought processes here, rather than a specific application. Imo, a bit more serious study of basics would help, rather than what seem to be random questions to PF.
 
  • #35
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Well I can't tell why Sophie thought I was thinking about rpm measuring. All I said is that the method of putting a permanent magnet and then spinning the rotor which uses a homopolar disc for the induction of current for the transfer of power wont work , because it would spin in a uniform b field and it could only induce current in the disc if it had brushes attached to it.

As you said Nascent the idea was to get a few kW to a rotor without using brushes or slip rings.So I first talked about the rotating capacitor then we concluded that it is only logical if we use some kind of high dielectric constant material and that and alos a few other things would complicate its workings , even though it would take up much less space and use much less metal than with coils.

So I guess I'm back where I first were.Two multi layer (each layer laminated and isolated from the other) discs at each end of a rotor connected with a winding that sits on some armature mounted on the rotor.two stationary coils at each end of the rotor were the discs are and a stator winding , couple the stator winding to the windings at each end of the rotor with a capacitor and I get a rotating energy producing oscillator, the frequency then determined by the value of the capacitor and the rpm.

Yes your right sophie a drawing or a schematic would benefit greatly , also there are a few things I havent mentioned , anyways the idea is to use high current high frequency low voltage in the rotor and much higher voltage , lower current and the same high frequency in the stator.
depending on the efficiency of the induction part at the discs and coils at each end of the rotor this could be a pretty good compact high frequency ac genberator , output can then be either fed into a ferrite core traffo for any desired output voltage and then rectified or simply rectified to DC
 
  • #36
sophiecentaur
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Yes your right sophie a drawing or a schematic would benefit greatly
So let's wait until you produce a picture and we will have a better idea of what you actually want. It is too much of a moving target for you to expect proper answers.
 
  • #37
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Well then I guess if using high frequency inductive coupling is better since I get no wearing parts except the shaft bearings.

I guess theres nothing else one can do about this situation except a comutator/slip rings or em induction.

Go out and find an old VCR inside you will find a rotating head that is coupled to outside power through a rotating transformer. The power is quite low but it works and is in common use. Hope this helps.
 
  • #38
NascentOxygen
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Go out and find an old VCR inside you will find a rotating head that is coupled to outside power through a rotating transformer. The power is quite low but it works and is in common use. Hope this helps.
Scavenging and repurposing should always be the source of first choice!
 

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