Where the OVERUNITY using INDUCTION COILS comes from (eg Joule Thief)

[lancaIV]

https://en.wikipedia.org/wiki/Universal_motor
.....

Torque-speed characteristics

Series wound electric motors respond to increased load by slowing down; the current increases and the torque rises in proportion to the square of the current since the same current flows in both the armature and the field windings. If the motor is stalled, the current is limited only by the total resistance of the windings and the torque can be very high, and there is a danger of the windings becoming overheated.
The counter-EMF aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant, the counter-EMF is zero and the only factor limiting the armature current is the armature resistance.
Usually the armature resistance of a motor is low; therefore the current through the armature would be very large when the power is applied. Therefore the need can arise for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-EMF. As the motor rotation builds up, the resistance is gradually cut out.
The speed-torque characteristic is an almost perfectly straight line between the stall torque and the no-load speed. This suits large inertial loads as the speed will drop until the motor slowly starts to rotate and these motors have a very high stalling torque.^[5]

As the speed increases, the inductance of the rotor means that the ideal commutating point changes. Small motors typically have fixed commutation. While some larger universal motors have rotatable commutation, this is rare. Instead larger universal motors often have compensation windings in series with the motor, or sometimes inductively coupled, and placed at ninety electrical degrees to the main field axis. These reduce the reactance of the armature, and improve the commutation.^[4]

One useful property of having the field windings in series with the armature winding is that as the speed increases the counter EMF naturally reduces the voltage across, and current through the field windings, giving field weakening at high speeds. This means that the motor has no theoretical maximum speed for any particular applied voltage.

Universal motors can be and are generally run at high speeds, 4000-16000 rpm, and can go over 20,000 rpm.^[4] By way of contrast, AC synchronous and squirrel cage induction motors cannot turn a shaft faster than allowed by the power line frequency. In countries with 60 Hz(cycle/Sec) AC supply, this speed is limited to 3600 RPM.^[6]

Motor damage may occur from over-speeding (running at a rotational speed in excess of design limits) if the unit is operated with no significant mechanical load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated into the motor's protection and control schemes. In some smaller applications, a fan blade attached to the shaft often acts as an artificial load to limit the motor speed to a safe level, as well as a means to circulate cooling airflow over the armature and field windings. If there were no mechanical limits placed on a universal motor it could theoretically speed out of control in the same way any series-wound DC motor can.^[2]

[tinman]

author=lancaIV link=topic=17297.msg508313#msg508313 date=1500206758]
https://en.wikipedia.org/wiki/Universal_motor
.....

Torque-speed characteristics

Series wound electric motors respond to increased load by slowing down; the current increases and the torque rises in proportion to the square of the current since the same current flows in both the armature and the field windings. If the motor is stalled, the current is limited only by the total resistance of the windings and the torque can be very high, and there is a danger of the windings becoming overheated.
The counter-EMF aids the armature resistance to limit the current through the armature.

When power is first applied to a motor, the armature does not rotate. At that instant, the counter-EMF is zero and the only factor limiting the armature current is the armature resistance.

Usually the armature resistance of a motor is low; therefore the current through the armature would be very large when the power is applied. Therefore the need can arise for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-EMF. As the motor rotation builds up, the resistance is gradually cut out.
The speed-torque characteristic is an almost perfectly straight line between the stall torque and the no-load speed. This suits large inertial loads as the speed will drop until the motor slowly starts to rotate and these motors have a very high stalling torque.^[5]

As the speed increases, the inductance of the rotor means that the ideal commutating point changes. Small motors typically have fixed commutation. While some larger universal motors have rotatable commutation, this is rare. Instead larger universal motors often have compensation windings in series with the motor, or sometimes inductively coupled, and placed at ninety electrical degrees to the main field axis. These reduce the reactance of the armature, and improve the commutation.^[4]

One useful property of having the field windings in series with the armature winding is that as the speed increases the counter EMF naturally reduces the voltage across, and current through the field windings, giving field weakening at high speeds. This means that the motor has no theoretical maximum speed for any particular applied voltage.

Universal motors can be and are generally run at high speeds, 4000-16000 rpm, and can go over 20,000 rpm.^[4] By way of contrast, AC synchronous and squirrel cage induction motors cannot turn a shaft faster than allowed by the power line frequency. In countries with 60 Hz(cycle/Sec) AC supply, this speed is limited to 3600 RPM.^[6]

Motor damage may occur from over-speeding (running at a rotational speed in excess of design limits) if the unit is operated with no significant mechanical load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated into the motor's protection and control schemes. In some smaller applications, a fan blade attached to the shaft often acts as an artificial load to limit the motor speed to a safe level, as well as a means to circulate cooling airflow over the armature and field windings. If there were no mechanical limits placed on a universal motor it could theoretically speed out of control in the same way any series-wound DC motor can.^[2]

And there you go.


Brad

[tinman]

And you seem to think that that is a good thing,,,

Just because we use things in a certain way does not mean that we must,,

So indeed,, there ya go.

WHY???



The self induced moment is from the inrush of current flow,, the magnetic induced part is the change in flux density the coil sees from the magnetic field,,,,,

Now think this one over,,  change the way you are looking at it,, so if you want it to speed up and maintain its full torque potential you would need to have the full amps passing,, not a reduced quantity of charge,, you and tinman keep on talking about reducing current flow to limit speed, ask yourself why, not how it happens but why would you want to limit the current flow and the torque just to control the speed.

I do not say any such thing.

This is not rocket science,and it seem's that no mater how simply i try to explain myself,your just not getting it.

I have said time and time again-->the more BEMF that can be retained under any mechanical load placed on the motor,the more efficient that motor is.
You seem to be stuck on the fact that the more current you pump into a motor,the more torque that motor will deliver,and you assume the best way to do this,is to remove as much of the BEMF as you can,when in actual fact,the more BEMF the motor can produce,the more torque it will have,while drawing less current from the power supply--so you have things ass about Webby.

AND if you actually read what was written you would see that if there was no BEMF\CEMF then the motor would run with a constant torque, with a constant amp draw and spin up to oblivion.

Thats not what was said at all.
Quote: If there were no mechanical limits placed on a universal motor it could theoretically speed out of control in the same way.

If there was no BEMF,then the motor would constantly draw the maximum current value allowed by the winding resistance only.
So now,get your self a universal motor,lock the shaft so as it cannot rotate,plug it in,and see how long it last's--this is your motor with no BEMF--a big resistive heater that wouldnt last 1 minute before it smoked up.

Why would you want to take that approach to reducing\controlling the BEMF\CEMF,, excuse my blunt response but that method is just stupid,, and I am surprised that Brad is not jumping on you a little on this setup,, he knows a little about how it responds.

Yes,that is a little out of the ball park,and not all correct.
But what it will show you,is what happens to the current draw when you remove the self induced EMF(BEMF).

So let me ask you these two questions Webby--and think about them carefully.
we have a motor that is being supplied 10 volts,and has a winding resistance of 1 ohm
1-What would the current draw be from the power supply, if that motor produced the same amount of BEMF as the applied EMF ?
2- What would be the value of the current flowing through the windings?


Brad
2-

[citfta]

And you seem to think that that is a good thing,,,

Just because we use things in a certain way does not mean that we must,, AND if you actually read what was written you would see that if there was no BEMF\CEMF then the motor would run with a constant torque, with a constant amp draw and spin up to oblivion.

Your answer is incorrect.  If there is no BEMF,  THERE IS NO TORQUE!

Why would you want to take that approach to reducing\controlling the BEMF\CEMF,, excuse my blunt response but that method is just stupid,, and I am surprised that Brad is not jumping on you a little on this setup,, he knows a little about how it responds.

Well, you got one thing right.  To do that would be stupid.  It was an example to try and get you to understand the relationship between torque and BEMF.  But obviously it failed.  Why would Brad disagree with that?  That is the way motors actually work.  I am sorry you seem to be having such a hard time grasping the concept between torque and BEMF.  But you simply cannot have one without the other.  And I don't understand why you want to have a motor that is simply going to produce a lot of heat and no torque as Brad has already explained to you several times.

[lancaIV]

AC 60 Hz : 3600 RPM
AC 50 Hz : 3000 RPM

DC ?? : 3000-3600 RPM
pulsed DC

universal answer ?

how is a variable speed motor commanded ?