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## Solid States Devices => solid state devices => Topic started by: forest on January 08, 2009, 11:51:21 PM

Title: AC motor questions
Post by: forest on January 08, 2009, 11:51:21 PM
I have a couple of questions about AC motors and not only. Please do not say it's off topic here, because I'm a noob in electronics.

I think that questions are important and we ALL should rethink the answers.

This topic is continuation of my investigations (as a noob) moved here from 'Infinity coil' topic.
You will soon see however that it's related to all topics in this section.

First : I learned that we have rotating magnetic field in 2 phase AC motor. Wonderful! Could it be
the same magic like in Hubbard coil, TPU ring, Hendershot motor,Searl generator and many others ?

Second : Seems unrelated but may influence our investigations I think. I talked with my friend who is a good electrician (and a patient man)  about two currents of the same frequency.
The questions are :
1. Can we put two AC exactly of the same frequency and in phase through the same conductor ?
2. Can we put two AC of the same frequency but shifted in phase through the same conductor ?

He told me that 1 is impossible but 2 is possible and very common ? Is that true ?
Title: Re: AC motor questions
Post by: forest on January 09, 2009, 12:49:53 PM
Seems that nobody is interested. I would explain my idea.
If we could put more then one current of the same frequency but shifted in phase into electric circuit, then next question in chain  is as follows :

do we have each current separately and can extract each of two and use it's power ? I think the answer is yes.
two currents (each representing a part of electric power) flowing in circuit but each of them is separate.
but can we join them to sum their power ?
normally we can't because of phase difference, the current in one is small when the other is big and so on, the result is a mixed  mess something like noise or average power cut.

Apparently we have no hope, and even we will work out how to shift phases again what it would do for us ? Somebody will say : not much . I disagree...

Think a moment please and support my conclusions with open mind and knowledge I'm lack of.
Title: Re: AC motor questions
Post by: Charlie_V on January 09, 2009, 07:35:41 PM
Quote
First : I learned that we have rotating magnetic field in 2 phase AC motor. Wonderful! Could it be
the same magic like in Hubbard coil, TPU ring, Hendershot motor,Searl generator and many others ?

I don't follow any of these motors so I couldn't help you in the comparison. However, I know a little bit about motors in general.  A rotating magnetic field means you have coils lined in a circle with one pole facing inward and you are energizing each coil in a particular pattern in time.  For a 2 phase motor then there are 2 different groups of coils being alternated on/off.  While one group is on, the other is off.  For a 3 phase or 4 phase etc. the groups are turned off and on with on/off times slightly overlapping the next group.  This is the rotating magnetic field they are talking about - its not magic at all.

Quote
Second : Seems unrelated but may influence our investigations I think. I talked with my friend who is a good electrician (and a patient man)  about two currents of the same frequency.
The questions are :
1. Can we put two AC exactly of the same frequency and in phase through the same conductor ?
2. Can we put two AC of the same frequency but shifted in phase through the same conductor ?

He told me that 1 is impossible but 2 is possible and very common ? Is that true ?

Your friend is wrong, you can do both.  In the first case, the two AC frequencies will add and the voltages/currents along the conductor will be larger.  In the second case, the voltages along the conductor will be decreased depending on the phase difference.  At 180 degrees, the voltages/currents along the conductor will be canceled.

To do either, a simple experiment is to get a 2 function generators, a long piece of wire and an oscilloscope.  Connect the positive terminals of each function generator to one end of the long wire, connect the oscilloscope to the other end - you can either ground the o-scope and function gens together or leave them floating, it doesn't matter (although floating you'll pick up 60Hz).  Starting out by keeping only one function generator on, the other off.  Start changing the frequency until you get maximum voltage at the end where the oscilloscope is - record that frequency.  Turn the other function generator on and set it to that frequency.  Then adjust the phase of one of the function generators (the expensive function generators have a phase option).  You'll notice that the voltage maximum read by the oscilloscope can be made larger (when the two are in phase) and smaller (when the two are out of phase).  You may also see, depending on how close you can get the function generator frequencies to match), a slight beat frequency.  Although the closer the 2 f-gens are to one another, the slower the beat will be.

You'll need either a very long wire or high frequency func. gens.  For 3 meters (~9feet) of wire you should see a maximum voltage at the other end around 25MHz.  Although it will probably be much lower than that because of the added impedance of the oscilloscope and the low inductance of the single wire.  The voltage at the end of the wire will be close to 2 times the input voltage - you will be making an electrical standing wave on the wire.  Therefore, with both function generators going together and IN PHASE, both inputting 1 volt peak to peak, the output should be near 4 volts peak to peak as read by the o-scope.

If you coil your long wire around a plastic tube, and keep a little space between each turn, the output will no longer be 2 times the input voltage but many more times - you'll have to adjust the frequency a little to get the maximum voltage seen by the o-scope of course.  This is because you'll be turning your coil into a resonant cavity.  This means that the AC waves entering the coil get reflected back and forth within the coil (unlike the uncoiled wire where they reflect from the end only once).  So as the AC wave train enters the coil, they add to the next.  In a sense you are using 1 AC wave, trapping it within the coil, and allowing it to add to itself over and over.  If you inject another AC wave, it will do the same and the phase of second AC wave will either add or cancel the like before.

Hope that helps,
Charlie
Title: Re: AC motor questions
Post by: nueview on January 09, 2009, 08:11:11 PM
what you are asking here seems to be a point not often discussed. logic and practicle experience so here is 35 years of practicle experience of what i know.

most DC resistive circuit components do not show a large current rise upon connection to a voltage source emf (voltage) and mmf (current) seem to move as a steady state of affairs coming to some balance and conclusion to flow were heat is generated as units according to the volume moving and its resistance to mmf. and i assume mmf and emf as wave theory present only minor external effects due to short strait runs of the circuit and capacitors seem to charge along a logrithmic ratio all these appear correct except inductors they seem to slow current in relation to field growth and then find steady flow as influence stabilizes.

In AC circuits most of the components react the same as if they were still in a DC circuit but here inductors seem to have a magnified effect almost as if in the first instant an inductor sees only the wire resistance and then as the feild influence grows they appear to gain and drip off as if the resistance is pulled from the surrounding medium which is set in motion as faradays law would suggest.

this then would seem to go along tesla's line of thought for there being only transverse and logditudinal waves how many or much transverse wave energy would have to be generated to suppress one ampere of current flow through an adjacent inductor or wire. but this would be faradays law and lentz law in conjunction if only it didn't work this way there would be no electric at all. so be glad lentz law works as it does.

in motors the windings can move reducing there interaction producing speed and reducing there interaction allowing mor current to flow for a longer period of time making it more apparent how little resistance there is to current flow without its interaction to the stabilizing effect of voltage and current by there reactance.

as you are now so once i was and as i am hopefully you shall become.  It has taken me a long time to fight my way to the understanding i now have wish i hadn't fought it so hard.

i do enjoy answering your questions they really make me grow aware of the world i am in and my place in it. in thinking through my answers for you i seem to gain insite into things i have seen and they seem to become much clearer. i have not done this since my son died 5 years back.

here i will give you something to think about make a small stream fo water from a faucet place a magnet near it and notice any effects, then bring a charged peice of styrofoam cup near it and watch what happens.

if you can generate a good static charge put some sugar in a small pile on a sheet of aluminum and let the charge arc through the sugar and note what happens you may be supprized.

truly there are simple things to confound the wisdom of men.

Title: Re: AC motor questions
Post by: forest on January 09, 2009, 08:18:47 PM
I don't follow any of these motors so I couldn't help you in the comparison. However, I know a little bit about motors in general.  A rotating magnetic field means you have coils lined in a circle with one pole facing inward and you are energizing each coil in a particular pattern in time.  For a 2 phase motor then there are 2 different groups of coils being alternated on/off.  While one group is on, the other is off.  For a 3 phase or 4 phase etc. the groups are turned off and on with on/off times slightly overlapping the next group.  This is the rotating magnetic field they are talking about - its not magic at all.

Your friend is wrong, you can do both.  In the first case, the two AC frequencies will add and the voltages/currents along the conductor will be larger.  In the second case, the voltages along the conductor will be decreased depending on the phase difference.  At 180 degrees, the voltages/currents along the conductor will be canceled.

To do either, a simple experiment is to get a 2 function generators, a long piece of wire and an oscilloscope.  Connect the positive terminals of each function generator to one end of the long wire, connect the oscilloscope to the other end - you can either ground the o-scope and function gens together or leave them floating, it doesn't matter (although floating you'll pick up 60Hz).  Starting out by keeping only one function generator on, the other off.  Start changing the frequency until you get maximum voltage at the end where the oscilloscope is - record that frequency.  Turn the other function generator on and set it to that frequency.  Then adjust the phase of one of the function generators (the expensive function generators have a phase option).  You'll notice that the voltage maximum read by the oscilloscope can be made larger (when the two are in phase) and smaller (when the two are out of phase).  You may also see, depending on how close you can get the function generator frequencies to match), a slight beat frequency.  Although the closer the 2 f-gens are to one another, the slower the beat will be.

You'll need either a very long wire or high frequency func. gens.  For 3 meters (~9feet) of wire you should see a maximum voltage at the other end around 25MHz.  Although it will probably be much lower than that because of the added impedance of the oscilloscope and the low inductance of the single wire.  The voltage at the end of the wire will be close to 2 times the input voltage - you will be making an electrical standing wave on the wire.  Therefore, with both function generators going together and IN PHASE, both inputting 1 volt peak to peak, the output should be near 4 volts peak to peak as read by the o-scope.

If you coil your long wire around a plastic tube, and keep a little space between each turn, the output will no longer be 2 times the input voltage but many more times - you'll have to adjust the frequency a little to get the maximum voltage seen by the o-scope of course.  This is because you'll be turning your coil into a resonant cavity.  This means that the AC waves entering the coil get reflected back and forth within the coil (unlike the uncoiled wire where they reflect from the end only once).  So as the AC wave train enters the coil, they add to the next.  In a sense you are using 1 AC wave, trapping it within the coil, and allowing it to add to itself over and over.  If you inject another AC wave, it will do the same and the phase of second AC wave will either add or cancel the like before.

Hope that helps,
Charlie

Thank you. Is there any reason why we can't use two generators to sent then same frequency and phase currents into transformer and output from the transformer feed back as a replacement for one of those generators  ? That way one of the generators is needed only at start and such transformer will continuously output current of bigger and bigger voltage or amperage probably up to damage or core saturation .
Does it makes sense ?
Title: Re: AC motor questions
Post by: nueview on January 09, 2009, 08:31:23 PM
love what you just showed i have seen this used for motor demonstrations before they are simple and yet quite elligent but not real practicle but they do work perhaps something is missing in our understanding about this phenominas possible uses for motive power.

Title: Re: AC motor questions
Post by: Charlie_V on January 09, 2009, 09:28:41 PM
Quote
Thank you. Is there any reason why we can't use two generators to sent then same frequency and phase currents into transformer and output from the transformer feed back as a replacement for one of those generators  ? That way one of the generators is needed only at start and such transformer will continuously output current of bigger and bigger voltage or amperage probably up to damage or core saturation .
Does it makes sense ?

I think I see what your saying.  A transformer only converts voltage to current or current to voltage, the power or energy in the transformer is the same (Power = Voltage x Current).  So you can take 50 Watts of power and produce 5000 Volts but the maximum current your load can draw would be 0.01 Amps.  If your load requires more current than that (i.e. your load is a very small resistance), the power source will not be able to supply it and the voltage in the transformer will begin to drop.  Likewise, with 50 Watts you can transform the voltage to 0.005V and the current available will be 10,000 Amps.  Of course you'd need very thick wires of very low resistance to handle that much current without over heating and melting the transformer's wire - your load would need to be a very low resistance too).

So getting back to your question, two generators hooked to one transformer will just double the amount of power that a single generator could produce.  The transformer does not create energy, it is only a pressure/flow converter.  So feeding back the output of the transformer even if it is high voltage, will not be able to take the place of a generator.  This is mainly because the losses in the system bring the operation down to below 100%.  If you had 100%, then no loss would be in the generator, and you could close the loop as long as you didn't pull any energy from the system.

Sorry this is a little confusing to grasp at first.  The REAL reason as to why the transformer cannot be fed back is because of something called Lenz's Law.  All that means is that the output coil of the transformer tries to oppose the input coil.  So if the input coil is generating a north pole, the output coil ALSO generates a north pole, so that the flux within the transformer cancels - please be aware that this ONLY happens when there is a load on the output circuit; without a load no magnetic field is generated in the output coil, only a voltage.  The output coil tries to match the exact magnetic field value as the input coil (only because of losses it is always slightly less in value than the input).  That way, the power delivered to the output circuit is slightly smaller than the input circuit - does this make sense?  The exact same effect is also found in motors/generators as well.  Only in those machines, the input coils try to stop the rotor from moving - but its the same effect, they are trying to cancel the changing magnetic field of the output - whether the output's changing magnetic field comes from a coil or a rotating permanent magnet.  Many people, including myself, are looking for ways to fool the output circuit so that it reacts to a bigger change than what it sees, or that its reaction cannot affect the input - I've had some success with the later, but no O.U. as of yet.

Charlie
Title: Re: AC motor questions
Post by: nueview on January 10, 2009, 04:39:43 AM
charlie

if you put capacirors across the primary of the transformer so it becomes a tank circuit drawing current off the secondery will alter the inductance of the primary and allow more current to flow from it to the secondary but if the frequency floots up at the same time what would be the end result. is current then proportional or not any ideas on this at all.

martin
Title: Re: AC motor questions
Post by: forest on January 10, 2009, 12:07:13 PM
I think I see what your saying.  A transformer only converts voltage to current or current to voltage, the power or energy in the transformer is the same (Power = Voltage x Current).  So you can take 50 Watts of power and produce 5000 Volts but the maximum current your load can draw would be 0.01 Amps.  If your load requires more current than that (i.e. your load is a very small resistance), the power source will not be able to supply it and the voltage in the transformer will begin to drop.  Likewise, with 50 Watts you can transform the voltage to 0.005V and the current available will be 10,000 Amps.  Of course you'd need very thick wires of very low resistance to handle that much current without over heating and melting the transformer's wire - your load would need to be a very low resistance too).

So getting back to your question, two generators hooked to one transformer will just double the amount of power that a single generator could produce.  The transformer does not create energy, it is only a pressure/flow converter.  So feeding back the output of the transformer even if it is high voltage, will not be able to take the place of a generator.  This is mainly because the losses in the system bring the operation down to below 100%.  If you had 100%, then no loss would be in the generator, and you could close the loop as long as you didn't pull any energy from the system.

Sorry this is a little confusing to grasp at first.  The REAL reason as to why the transformer cannot be fed back is because of something called Lenz's Law.  All that means is that the output coil of the transformer tries to oppose the input coil.  So if the input coil is generating a north pole, the output coil ALSO generates a north pole, so that the flux within the transformer cancels - please be aware that this ONLY happens when there is a load on the output circuit; without a load no magnetic field is generated in the output coil, only a voltage.  The output coil tries to match the exact magnetic field value as the input coil (only because of losses it is always slightly less in value than the input).  That way, the power delivered to the output circuit is slightly smaller than the input circuit - does this make sense?  The exact same effect is also found in motors/generators as well.  Only in those machines, the input coils try to stop the rotor from moving - but its the same effect, they are trying to cancel the changing magnetic field of the output - whether the output's changing magnetic field comes from a coil or a rotating permanent magnet.  Many people, including myself, are looking for ways to fool the output circuit so that it reacts to a bigger change than what it sees, or that its reaction cannot affect the input - I've had some success with the later, but no O.U. as of yet.

Charlie

Thank you. Let's summarize. Is Lenz's law the only reason (beside of resistance of wires) that we cannot feed output current back to the primary  ?
I think we should follow open mind path of investigation: instead of quote exact law, we should point what would happen if we have a way to exclude the effects of such law.
What else we need to overcome , to feed back output current from transformer to the input ? I can only imagine that  we should work out some overrun protection to limit accumulated current/voltage rise cause by positive feedback and influence on generator (or a way to remove even that single generator which is left)

Current situation:

1. We have two generators outputting exactly the same AC current into transformer . This is easily done.
2. We have to invent a way to eliminate or restrict Lenz law effects
3. We then feed back output current into primary and turn off one of the generator while protecting the other from this back current (somehow I feel that this current may look at generator as a path to ground with less resistance then a transformer)
I have a feeling also that this output current should be maybe "prepared" to match phase and frequency of input ? Am I wrong ?
4. The result is TWICE the power at output of transformer compared to the input from  generator (second generator is needed only for start)  AT EACH turn of feedback. Soon it will destroy transformer or generator.

I'm strongly convinced that such positive feedback is something we were learned to eliminate but it's the way to OU obviously.

Now it's time to point any flaws in that argumentation... Could you also tell me something about Lenz's law ? I'm interested if this is electric or magnetic effect : in other words what is opposed FIRST, what is the origin or this law, and if this is principle law or just a rule from experiments. I will try to read about it but I'd like to know your opinions.

Title: Re: AC motor questions
Post by: Charlie_V on January 12, 2009, 06:08:36 PM
@nueview

Adding capacitors can do a number of interesting things.  Mainly, it will be like adding a filter.  Basically if your input Ac frequency does not match the resonance of the secondary, the secondary will weed it out and you won't see much on the other side.  That of course is only half the story.  Because if you match the secondary resonant frequency to the AC input of the primary, you still may not get REAL power (in the sense that the voltage and current in the secondary can be out of phase if the values of your secondary inductance and capacitance do not equal (or the ratio does not equal) that of the primary circuit.)

@forest

To my knowledge Lenz's Law is the ONLY thing restricting it.  Sure resistance will too, but if lenz's law didn't exist then the resistance would have to be REALLY big to stop the feed back.  Personally, I don't like to refer to the effect as a law because it makes it sound like nature is following a "law" of man - when in reality its the man made "law" that follows nature.

All it means is that when a coil sees a changing magnetic field, it tries stop the change by countering it with its own magnetic field.  So if a north pole approaches a coil, and the coil is shorted (i.e. Loaded) the coil will generate a north pole that tries to push the approaching magnet away (or slow the approaching north pole down).  Likewise, if it was an approaching south pole, the coil would generate a south pole.  If a north pole tries to move away from the coil, the coil will generate a south pole and try to pull it back.  So if a magnet is rotated near a loaded coil, the coil will try to slow its rotation - this is what lenz's law describes.  If there is no load on the coil (the coil is open circuit), only a voltage develops.  The coil will not produce an opposing magnetic field because current can not flow in the coil due to it being an open circuit.  But the sign of the voltage will show you which way the current will flow when loaded.  And the current always flows in a direction to create an opposing magnetic field.

The best way to understand it is to FEEL it for yourself.  Take a thick aluminum or copper ring (hard drives have them or you can make it out of wire) just a donut of metal really.  Then get yourself a very strong rare earth magnet.  Now move either the magnet or the ring so that the magnet goes through the center of the ring.  You'll feel a force that pushes against the moving coil/magnet as it approaches, and pulls it back as it leaves.   Make sure the magnet is either much larger than the ring, or the magnet fits perfect inside the ring.  If its a really tiny magnet, or if the ring is too small, you won't feel the force.

Once you can find a way around this effect, then you'll have to worry about feed back problems.  Until then, don't sweat it  :D

Charlie
Title: Re: AC motor questions
Post by: nueview on January 12, 2009, 08:22:53 PM
i need to write this today for several reasons one being that this may answer another problem i am having.
charlie you stated that when current can't flow a voltage is developed surely this would develope a current at right anlge to the inducing force or flow to the voltage which is it faraday or lentz law that takes presodence in these field reactions.
faradays law states that currents moving in the same direction tend to magneticly couple and or pull together while currents moving in opposite directions tend to move apart. there is a law governing magnetic fields that states that a magnetic field is strongest when its lenght is least or at its minimum. so it would be logical to assume that currents moving in opposite directions which repell and scatter each other would be driven by voltages of charges that don't move in its simplest form you arrive at zero point energy so guess we just proved mr bearden correct. we could then assume that all matter would be constructed from a single charge or singularity from which all matter derives. and from which all matter can be destroyed by causing this charge to move. from this point it gets real complicated real fast and very complex so lets just let it go for now.
phased currents and voltages are then displaced entities allowing a new structuring to begin a form of redistribution of energy not always accountable for within a given system is this what you are stating?
Title: Re: AC motor questions
Post by: Charlie_V on January 12, 2009, 10:10:16 PM
@nueview

Faradays Law just says that a coil will produce a voltage when the coil sees a changing magnetic field.  Lenz's Law determines the direction the voltage sets up (which ultimately determines which way the current flows when the coil is loaded).

Sorry, I'm not sure I follow you fully though.  I think what your asking is shouldn't charges move to make the voltage across the open coil when the coil sees a changing magnetic field.  And, why doesn't the moving charge produce a magnetic field when it does so?  My answer to that is I have no idea.  I suppose that when the coil is open the current and voltage are 90 degrees out of phase? So if a magnetic field is produced from the charges moving in an open circuit, it occurs when the magnet is in a the zero position and thus does not effect the movement of the magnet?  I've thought about this but have never been able to imagine it in my mind.

Quote
it would be logical to assume that currents moving in opposite directions which repell and scatter each other would be driven by voltages of charges that don't move in its simplest form you arrive at zero point energy so guess we just proved mr bearden correct

I'll have to think on that, it is very interesting.  As far as Bearden, I've never been able to follow him.  However, it should be only natural that energy can be created because energy exists.  How did it get here if it cannot be created?  The only logical explanation is that it is creatable - we only need to find out how.

Title: Re: AC motor questions
Post by: forest on January 13, 2009, 12:29:30 AM
I have one additional question about Lenz's law in AC motor. As I understood rotating magnetic field in stator induce rotating magnetic field in rotor, first by inducing current in rotor.This magnetic field in rotor has opposite polarity changes and a small lag depending on load put on shaft.
Is that correct ?

How this induced current in rotor looks like ?
Title: Re: AC motor questions
Post by: Charlie_V on January 13, 2009, 02:19:30 AM
@forest

Your describing an induction motor.  Not all electric machines use induction.  Basically an induction motor has shorted coils in the rotor.  Just like the case above where I was describing the force that you feel when you move an aluminum ring over a magnet, this is similar.  The stator coils produce a changing magnetic field (much like the moving magnet in my earlier example).  The shorted coils in the rotor try to oppose the changing magnetic field of the stator.  As they oppose, it produces movement of the rotor.  The rotor will start to get faster and faster until the speed of the rotor matches the rotating magnetic field of the stator.  When this happens, the rotor coils no longer see a changing magnetic field because they are spinning at the same rate that the stator is energized.  The stator looks like a static field, induction stops and the rotor slows down a little.  Once slowed down a little, the process starts again.  So at no load there is a slight difference between the rotating magnetic field of the stator and the speed of the rotor because of friction.  When you load the rotor, it becomes harder to rotate and the slip gets bigger.  The induced current looks like the stator current but it goes in the opposite direction and is slightly less in magnitude.
Title: Re: AC motor questions
Post by: nueview on January 13, 2009, 07:54:51 AM
charlie faradays law has several parts as does lentz law so to throw out any part is not prudent. if two magnetic fields are rotating out of phase with each other is there a voltage between the two i say yes are the currents in the same direction  possibly not else what is back emf can the two cancel yes do they have to probably not if used properly. lentz law works great for copper inducters or should i say conductors but isn't worth a thing for iron conducters or plastic do these not have emf's and magnetic fields of course they do so do faradays first laws apply to these fields were lentz law does not yes lentz law was for the defining of an electrical system not the whole system faraday was looking for the nature of energy not the system so my questions still stand from above. can i prove my questions yes
i am very much interested in getting this write as have seen to much to demonstrait that there is another answer and it is much simpler an answer so don't resite a law without including an exception where one applies.conduction and field values in copper allow lenz law to work but it is only good that far.
Title: Re: AC motor questions
Post by: forest on January 13, 2009, 08:32:02 AM
@forest

Your describing an induction motor.  Not all electric machines use induction.  Basically an induction motor has shorted coils in the rotor.  Just like the case above where I was describing the force that you feel when you move an aluminum ring over a magnet, this is similar.  The stator coils produce a changing magnetic field (much like the moving magnet in my earlier example).  The shorted coils in the rotor try to oppose the changing magnetic field of the stator.  As they oppose, it produces movement of the rotor.  The rotor will start to get faster and faster until the speed of the rotor matches the rotating magnetic field of the stator.  When this happens, the rotor coils no longer see a changing magnetic field because they are spinning at the same rate that the stator is energized.  The stator looks like a static field, induction stops and the rotor slows down a little.  Once slowed down a little, the process starts again.  So at no load there is a slight difference between the rotating magnetic field of the stator and the speed of the rotor because of friction.  When you load the rotor, it becomes harder to rotate and the slip gets bigger.  The induced current looks like the stator current but it goes in the opposite direction and is slightly less in magnitude.

Are you sure that this current in stator is not a pure sinewave just going in opposite direction ? Is that really multi phase current inside rotor ? Is there any way to check this ?
Because rotor has a slip and never goes so fast as stator rotating field and direction of rotor movement is the same as rotating magnetic field I assume that the polarity of magnetic field in rotor is opposite to stator field and it works by pulling rotor not by pushing it. Is that correct ?

Did anybody thought about reusing rotor current and put it back to stator ?
Title: Re: AC motor questions
Post by: Doug1 on January 13, 2009, 12:04:47 PM
Forest
Sort of ,I am working on placing tiny caps in the rotor to increase the potential in the rotor to see if will sync better and reduce the slip. I have not found suitable info on the shorted rotor coils so it seems it is time to wing it. I may just jump right to the rebuild of an alternator to fit the concept.
Title: Re: AC motor questions
Post by: Charlie_V on January 13, 2009, 06:03:33 PM
@nueview

Quote
lentz law works great for copper inducters or should i say conductors but isn't worth a thing for iron conducters or plastic

Lenz's Law is just to explain that induced currents from an alternating magnetic field are in opposition to the field that induced them.  Plastic is usually insulating and therefore will not have currents induced in it.  Iron is a conductor, typically with higher internal resistance, and the currents induced in it are also in opposition - just like copper.  That's why they use laminate transformer cores so that the eddy currents are reduced - the eddy currents are in opposition just like in copper.

The magnetic properties of these materials are different though - that's not what I'm talking about here.  When copper is placed in a STATIC magnetic field, the dipoles align to oppose the magnet - this is not the same as the magnetic field induced by a changing magnetic field.  Copper, water, graphite, plastic and many more are diamagnetic - this is a material property.  If any of these materials are conductive, and you place it in an alternating field, the induced currents will overpower the diamagnetic effect (which is very weak in almost all of these materials - pyrolytic graphite has the highest, better than bismuth, and the effect is still very small).

@forest
Quote
Are you sure that this current in stator is not a pure sinewave just going in opposite direction ? Is that really multi phase current inside rotor ? Is there any way to check this ?

I guess the current in the stator is a sine wave, if you drive the stator with a sign wave.  You could make it a square, triangle, impulse, anything really I suppose.  Its only multi-phase if you are driving it with more than one phase.  Oscilloscopes can be used to check it.

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Because rotor has a slip and never goes so fast as stator rotating field and direction of rotor movement is the same as rotating magnetic field I assume that the polarity of magnetic field in rotor is opposite to stator field and it works by pulling rotor not by pushing it. Is that correct ?

If your using the device as a motor it never exceeds the driving rotation.  However, if you use an external source (like a wind turbine) and drive the rotor faster than the rotating field of the stator, it becomes a generator and will supply power to the stator - pretty cool huh.  When in motor mode though, it does both pushing and pulling.  The only motor that works off of pure pulling is what is called a reluctance motor.  The rotor in a reluctance motor is laminated steel or iron and usually has groves in it to make it look like a star.  The coils in the stator attract the rotor and then get turned off so the rotor spins past the coil and then they energize again.  I think these are really efficient compared to induction motors - not as efficient as permanent magnet motors though (they are the best efficiency wise).  The problem with reluctance motors is that they cannot act as a generator.

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Did anybody thought about reusing rotor current and put it back to stator ?

The current in the rotor is normally in the opposite direction as the stator.  They would cancel each other and nothing would turn.  BUT, that's an interesting idea.  You might be able to shift the phase or something and utilize it.  I'd have to think about it - good thought!
Title: Re: AC motor questions
Post by: Charlie_V on January 13, 2009, 06:14:12 PM
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Did anybody thought about reusing rotor current and put it back to stator ?

Actually, they do - sort of.  Look up universal motors.  These have the rotor coils in series with the stator so they use the same current to rotate.  The cool thing about universal motors is that if they do not have a load, they will spin so fast they destroy themselves!  There might be a way of using that to an advantage.