Rotating Magnetic Field's and Inductors.

[TinselKoala]

I don't know how many times I've posted a link to that same webpage with the inductance calculator on it.

Some inductance meters are very sensitive to applied voltage. When you are moving a magnet near a coil, even if slowly, you are inducing a voltage in the coil.
See my video demonstration here:
http://www.youtube.com/watch?v=R5mvryt2kYg
This is an illustration of Faraday's Law of Induction. A moving magnet creates a time-rate-of-change in the magnetic flux linking the coil, and so induces a voltage. A stationary magnet does not cause a rate of change of flux so does not induce a voltage.
This induced voltage will affect those inductance meters that are very sensitive to voltage. (It may even damage them permanently).
Perhaps this induced voltage is what explains TinMan's results with his meter.

The "normal" result is what Poynt99 reports. As an unsaturated core is subjected to a magnetic field from an external magnet, it is brought nearer and nearer to saturation (changing permeability). This means its inductance goes down. A fully saturated core is essentially equivalent to an air core as far as influencing the inductance of a coil wrapped around it. This effect does not depend on motion (change in flux) but is only related to the "quantity" or magnitude of magnetic flux in the core. So the inductance will change while the magnet is being moved but when the magnet stops moving the inductance will remain at that value it had at the instant of stopping.

As inductance goes down, the resonant frequency of the coil (or tank circuit with the coil and capacitor) will go up. As associated capacitance goes down, the frequency goes up. Frequency is inversely related to both capacitance and inductance. So if you bring a magnet close to a resonating ferrite-cored coil, its frequency should go up, since the inductance goes down. Inserting a high-permeability core material into an air-core coil makes its inductance go up, so its resonant frequency goes down. This is the basis of operation of the "loopstick" style tunable inductors which I have demonstrated several times.

The amount of change in frequency for a given applied magnetic field is a function of the core's permeability. So with an air core coil, you get no change in inductance from an external magnet since the applied magnetic field doesn't change the permeability of the air core.

[Magluvin]

I don't know how many times I've posted a link to that same webpage with the inductance calculator on it.

Some inductance meters are very sensitive to applied voltage. When you are moving a magnet near a coil, even if slowly, you are inducing a voltage in the coil.
See my video demonstration here:
http://www.youtube.com/watch?v=R5mvryt2kYg
This is an illustration of Faraday's Law of Induction. A moving magnet creates a time-rate-of-change in the magnetic flux linking the coil, and so induces a voltage. A stationary magnet does not cause a rate of change of flux so does not induce a voltage.
This induced voltage will affect those inductance meters that are very sensitive to voltage. (It may even damage them permanently).
Perhaps this induced voltage is what explains TinMan's results with his meter.

The "normal" result is what Poynt99 reports. As an unsaturated core is subjected to a magnetic field from an external magnet, it is brought nearer and nearer to saturation (changing permeability). This means its inductance goes down. A fully saturated core is essentially equivalent to an air core as far as influencing the inductance of a coil wrapped around it. This effect does not depend on motion (change in flux) but is only related to the "quantity" or magnitude of magnetic flux in the core. So the inductance will change while the magnet is being moved but when the magnet stops moving the inductance will remain at that value it had at the instant of stopping.

As inductance goes down, the resonant frequency of the coil (or tank circuit with the coil and capacitor) will go up. As associated capacitance goes down, the frequency goes up. Frequency is inversely related to both capacitance and inductance. So if you bring a magnet close to a resonating ferrite-cored coil, its frequency should go up, since the inductance goes down. Inserting a high-permeability core material into an air-core coil makes its inductance go up, so its resonant frequency goes down. This is the basis of operation of the "loopstick" style tunable inductors which I have demonstrated several times.

The amount of change in frequency for a given applied magnetic field is a function of the core's permeability. So with an air core coil, you get no change in inductance from an external magnet since the applied magnetic field doesn't change the permeability of the air core.

Hey Tk

If the magnet is just passing tdc and then the coil pulses to push the magnet, isnt the coils field countering the magnets field thus lessening the possibly near saturation point of the core while the coil is on?

Mags

[MileHigh]

No Webby, I stand by my statement.  The statement by Brad taken at face value is wrong.  It goes back to the title of the original YouTube clip, "Proof that Magnetic Fields Increase Efficiency in Pulse Motors."  That's another generic statement and it's wrong and not true.  Even the title of the clip is too vague.  It should be something like "Proof that Magnetic Fields from the Action of a Spinning Rotor Increase the Efficiency of the Coil of a Pulse Motor."

The qualified statement with special conditions is true.  But there is no going backwards and saying, "But I really meant...."

People should not be almost petrified about respectfully disagreeing with each other or challenging each other's statements.  That's what a forum is supposed to be all about.

[TinselKoala]

Hey Tk

If the magnet is just passing tdc and then the coil pulses to push the magnet, isnt the coils field countering the magnets field thus lessening the possibly near saturation point of the core while the coil is on?

Mags

I was just about to address this issue, so I'm glad you brought it up.

Consider a rotor with magnets, turning inside a ring of cored stator coils. First, just spin the rotor but don't provide any power to the coils. Consider what happens to the inductances of the coils, and the induced voltages in the coils. The inductance goes down as a magnet approaches the coil and goes back up as the magnet recedes from the coil. This effect does not depend on polarity of the magnet. But also, as the magnet approaches the coil it induces a voltage in the coil, that increases up to the nearest approach, then flips sign and decreases as the magnet goes away again. (Faraday's Law in action again.) This effect _does_ depend on the polarity of the magnet facing the coil. That is, whether the voltage goes from + to -, or from - to + as the magnet passes, depends on which pole of the magnet is facing the coil as it moves past.

So you have a very complicated situation. In some configurations the induced voltage from the magnet's motion will aid the voltage applied to pulse the coil, and in other configurations it will oppose it. So depending on which pole of the magnet is facing the coil, and what polarity of voltage is applied to the coil to pulse it, you can have enhanced "pulling in" or reduced "pulling in" in an attraction-type pulse motor, and enhanced or reduced "pushing out" in a repulsion-type PM. If you have alternating rotor magnet polarities it gets really _really_ complicated. Then there is the effect of changing inductance/permeability from the approaching and receding magnets. These effects can aid or reduce the effects due to induced voltage!

The most interesting type of pulse motor that I know about is the Steorn Orbo core-effect motor. As you know, a carefully wound toroidal coil on a high-permeability core will not have much leakage of magnetic field when it is energized. So you wouldn't think it would be useful for attraction or repulsion type pulse motors, and it's not. BUT.... the magnetic field caused by energizing the coil does change the core's permeability... and this affects how strongly a magnet is attracted to the _core_. It isn't attracted to the magnetic field from energizing the core, but to the core material itself. So the Steorn Orbo core-effect motor works by having the rotor magnets attracted to the toroidal cores while the power is _off_ during the approach, and just at dead-center the power is turned _on_ and this _reduces_ the permeability of the core material, making it less attractive to the rotor magnet. So the magnet is pulled in more strongly as it approaches, than when it has passed and is receding. So the rotor speeds up. This core effect does not depend on polarity of either the voltage applied to the coil, or the polarity of the rotor magnet passing it! So you can have alternating rotor magnet faces, or same faces, to the toroidal coils and it will work the same.

[MileHigh]

Whatever MH,, I guess that adding those moving magnets did not improve the efficiency at all then,, right

No going backwards,,

Besides,, I am right and everyone else is wrong

Now for the question that I am getting myself turned around over,,

When the coil fires off,, is it trying to slow down the rotor by pushing it backwards or pulling it backwards or is it trying to speed it up,, I am referring to the start of the on pulse.

Come on, there is nothing wrong with being precise, this is the science of electronics.  If I said to you that when I add a drag to your electric bike in the form of an old-fashioned dynamo on the tire rubber to light an extra head lamp, and that action makes the electric bike more efficient in terms of distance per battery charge, you would look at me like I was nuts.  If you are old enough you might remember how it was noticeably harder to pedal your bike when the dynamo was engaged to power your headlamp.

To answer your question, the exact timing of the motor was never really established.  I stated that the eight poles effectively blended together into what looked like a four pole pulse motor and I am pretty sure that was the case.  All that Brad really had to do was make a small sensor coil the diameter of his rotor magnets placed 180 degrees away from the drive coil and positioned very close to the rotor.  He would then pick up the double pulse heartbeat, inverse heartbeat, heartbeat, etc, of the alternating poles passing the sensor coil.  Then with some basic scope work using that unambiguous timing reference the actual timing for the coil-rotor interaction could have been established.