Secret Of Back EMF

[Paul-R]

In motor control and robotics, the term "Back-EMF" often refers most specifically to actually using the voltage generated by a spinning motor to infer the speed of the motor's rotation for use in better controlling the motor in specific ways.[6]

To observe the effect of Back-EMF of a motor, one can perform this simple exercise. With an incandescent light on, cause a large motor such as a drill press, saw, air conditional compressor, or vacuum cleaner to start. The light may dim briefly as the motor starts. When the armature is not turning (called locked rotor) there is no Back-EMF and the motor's current draw is quite high. If the motor's starting current is high enough it will pull the line voltage down enough to notice the dimming of the light

https://www.youtube.com/watch?v=VfvfkXhHw04

I don't need to add any more, this says it all!

Tom

Is there any difference between your circuit and this ?

http://www.free-energy-info.com/Chapter6.pdf

Automotive Relay Battery Charger. Page 28

[tinman]

Tom and everyone,

Perhaps a simple way to distinguish between bemf and inductive kickback (IK) is to ask yourself, "does the effect take place simultaneously, or in sequence?"

bemf is a simultaneous phenomenon, whereas the IK effect takes place in a certain sequence of events. In a motor, the instant you apply power there is very little if any bemf generated, so the input current is high, but once the motor is running at speed, the applied emf, and bemf are in opposition simultaneously. When you are switching inductors, there is a definite sequence of events; i.e. you energize a coil, then remove the applied emf, then the coil tries to continue the current flow and as such reverses its output voltage, most often in a short high voltage spike. But that is determined by the load seen by the IK spike. THAT is IK.

So generally speaking, if you are switching/pulsing inductors, you are generating/collecting IK. If you are powering motors, the bemf effect is taking place, limiting the current into the motor. Without bemf, motors would draw huge amounts of current all the time.

Hope that clears things up a bit.

Thank you poynt.

[forest]

Read again all comments. Nobody here proved the direct relation between backEMF and inductive kickback.
I request please prove it with experiment. backEMF is going on when motor is running and inductive kickback  show up only when inductor is disconnected.
for example :

If we replace the capacitor collecting inductive spikes with a 1:1 transformer with low resistance windings, what voltage we get on secondary ? Does it depend on the speed of switching off motor coils ? There was stated coil and power supply are in series during inductive spike so what we should expect ? If energy collected in coil is due to backEMF , what is the limit of generated inductive spike voltage ? Obviously not 2x power supply voltage, so what is going on inside ? Transformation due to windings ratio ? or due to current change ratio ? or maybe due to resonance effect ?
Better yet, take just a coil and I'm asking what is the process of converting backEMF into inductive spike and on what it depends ?
If I use coil and set timing and then connect capacitor across coil would that change the output voltage of inductive spike ?


Questions are limitless..... I'm glad you know all answers according to modern theory, that's fine - you don't have suchn mess in head like I have....but....the theory boundary is the limit of clear thinking...

[MarkE]

Read again all comments. Nobody here proved the direct relation between backEMF and inductive kickback.
I request please prove it with experiment. backEMF is going on when motor is running and inductive kickback  show up only when inductor is disconnected.
for example :

If we replace the capacitor collecting inductive spikes with a 1:1 transformer with low resistance windings, what voltage we get on secondary ? Does it depend on the speed of switching off motor coils ? There was stated coil and power supply are in series during inductive spike so what we should expect ? If energy collected in coil is due to backEMF , what is the limit of generated inductive spike voltage ? Obviously not 2x power supply voltage, so what is going on inside ? Transformation due to windings ratio ? or due to current change ratio ? or maybe due to resonance effect ?
Better yet, take just a coil and I'm asking what is the process of converting backEMF into inductive spike and on what it depends ?
If I use coil and set timing and then connect capacitor across coil would that change the output voltage of inductive spike ?


Questions are limitless..... I'm glad you know all answers according to modern theory, that's fine - you don't have suchn mess in head like I have....but....the theory boundary is the limit of clear thinking...

Forest, there are literally thousands of academic references on the www for BEMF as it manifests:  1) As generator voltage, and 2) "Inductive kickback".  In the former case we have Faraday induction, and in the second self induction.  A DC motor can be modeled pretty accurately as a generator in series with an inductor and a resistor.

Inserting a transformer lets us change the voltage reference. 

An unclamped, rapidly switched inductor spikes up at a rate limited by the local parasitic capacitance and leakage current until something begins to conduct enough to carry the current.  Whatever the voltage reached determines the rate at which the current decays. 

[forest]

MarkE.. please correct me if I'm wrong , but if the voltage developed during inductive kickback of coil depends only on the time of decay, and if voltage is EMF or is caused by EMF, then why we are not talking about EMF if I saw equations stating that EMF generated depends on the rate of change of current ?


That is my fisrt question.


Then, secpnd question : if voltage or EMF / or the EMF itself is the result of inductive kickback then why we never see a kickback of large current instead of voltage ? Isn't that the EMF or voltage according to Ohm's law the force generating current across resistance ? What limit us to use some weird coil configuration during inductive kickback to get more amps instead of bigger voltage then the original power supply can do?
Or in other word : why I didn't saw video of Tesla coil generating lots of amps on secondary ? Impossible ? EMF is just a force, why it is limited to generating voltage spikes during inductive kickback ?