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

[lancaIV]

http://www.geminielectricmotor.com/About%20the%20Gemini%20Technology.htm

[citfta]

wrong, and I am trying to get you all to understand that in simple terms.
I did not say that Brad would be in disagreement,, I thought he has tried playing with a universal motor,, perhaps maybe even trying to augment the stator winding with a PM and a few other things.

I am not saying that you do not have one without the other,, I am pointing out what the limiting factor is that needs to be controlled in order to get the motor to produce the same torque at a higher RPM.

So tell me how much torque at the shaft you can have from a motor that is almost stalled compared to the torque from the same motor that is almost at its RPM limit,, where is all the BEMF in the almost stalled motor?

You certainly seem to be confused about how motors operate.  First you are wrong about motors not having the same torque at higher rpm.  As soon as you load the motor the current will increase to provide the torque and return the motor to the speed that produces the BEMF to again balance the applied voltage and torque requirements.  As you load the motor higher the current will again increase to give the torque necessary to keep the speed up.  As has been explained a couple of times already the BEMF acts like a governor to maintain the motor at a given speed based on the design of the motor and the applied voltage.

You are correct that in an almost stalled motor the BEMF is almost none existent.  BUT the agent which causes the BEMF is certainly there and that is the opposing magnetic field either from permanent magnets or energized coils.  If you remove the opposing magnetic field then you will have no torque.  So the same force that gives you the torque is also responsible for giving you the BEMF.

Let me propose another experiment for you.  Get a universal motor and disconnect the field coils from the armature.  Connect a variable power supply to the field coils.  Then connect another variable power supply to the armature brushes.  Now you can see for yourself the effect of varying the field coil current which will affect the torque and BEMF.  If you really want to learn you could also rig a simple prony brake to measure the torque.

Webby, I am perfectly willing to try and help you learn about motors.  But don't keep telling me I am wrong in what I post.  I made my living for over 40 years working on industrial machinery.  I have worked on hundreds of motors and motor controllers.  I have been factory trained on several of them.  If you don't agree with the way motors are being controlled then come up with a better way and you will never have to work again.  Today's motor controllers are very sophisticated devices used in industry for special purposes.  But the normal everyday motor still works on the very same principles I have been trying to get you to understand.

So, once again, the agent or force that gives a motor its torque is the same agent or force that causes BEMF.

Carroll

[citfta]

Webby,

Do you know what causes a motor to burn up?  You can burn up a perfectly good motor by overloading it.  How does that happen?  As I explained in the previous post a motor will draw more and more current to meet the torque requirement caused by the load on the motor.  If you overload the motor the motor will draw more current than the wiring of the motor was designed to handle.  Without some form of current protection such as a breaker or fuse the motor will overheat the wiring until the insulation of the wiring breaks down and then the motor shorts out and catches fire.

Another thing you seem confused about is when does a motor have the most torque.  Most AC induction motors actually have more torque when they are up to speed.  That is because the armature rotating at high speed has more current induced into it to create the opposing magnetic field.

DC motors on the other hand, because they have separate field coils that are fully energized from the beginning have starting torque equal to the running torque.  It is kind of amazing to see a large DC motor barely turning and yet moving a massive load.

[tinman]

is it me that is not getting what is being said??You keep saying that the weaker the motor the more efficient it is,, you keep heading into the electrostatic motor,, which if you wish to go there I can follow but I do not have a working testbed for that.


I am not assuming the best way is to remove the BEMF,, but rather control it, to USE it,, this is not rocket science after all


or
If the same motor were running at 10,000 RPM making 10N-m of torque or if it were running at 1,000 RPM making 10N-m of torque, which one is making more mechanical power,, it is that simple.


Now ask yourself, what is it that limits the RPM?,,  whatever it is that limits the RPM is what needs to be controlled and used to assist the motor in achieving a higher RPM with the same torque,, it is that simple.


Ask yourself a simple question,,  What is it that is wanted from a motor?
Ask yourself a simple question,,  What is the motor doing?

If the same motor had a draw of 1A or 10A,, which one would produce more shaft torque Brad,, it is that simple.

Well,it would seem that it is not that simple,as you are once again missing the point,and that point is-why do you want to decrease the BEMF ?
Some here think that by decreasing the BEMF,you make the motor more efficient-which,as i have stated right through this thread-you do not.

To answer your question-torque is not power.
The motor that is drawing only 1 amp,will do more useful mechanical work for a given electrical input value than that of the same motor drawing 10 amp's--it's that simple.
Reason being,the motor drawing 10 amp's will be dissipating a larger percentage of the input power as heat to that of the motor that is drawing only 1 amp.

So,the motor drawing only 1 amp converts more of the electrical input energy into mechanical energy than that of the motor drawing 10 amp's.

So,there is your answer--higher the BEMF,the more efficiently the motor converts electrical energy into mechanical energy.


Brad

[tinman]

I see that the point and methodology I am trying to get across is not making the trip,, so be it.

I  understand the working principles and am even comfortable with a lot of the math that goes along with it,, I am not confused nor am I missing it.

BEMF is the built in *limiter* for RPM,,

Edited before posting,, since it does not matter, apparently, anyway.

Well-what is your point Webby?
Why would you want to eliminate BEMF?


Brad