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Author Topic: Secret Of Back EMF  (Read 22448 times)

Offline TommeyLReed

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Secret Of Back EMF
« on: August 12, 2014, 08:16:28 PM »
Hi All,

I throught it would be a great test to show some basic back EMF test on this pulse motor. This is free extra energy while you add input energy.

https://www.youtube.com/watch?v=6BnHNdMzW2I

Tom

Free Energy | searching for free energy and discussing free energy

Secret Of Back EMF
« on: August 12, 2014, 08:16:28 PM »

Offline MarkE

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Re: Secret Of Back EMF
« Reply #1 on: August 12, 2014, 10:37:51 PM »
Tommey that's a nice video, but the conclusions are incorrect.  The energy recovered from the motor BEMF through the rectifiers into the capacitor bank all came from your power supply.  The motor operates as a generator that you tap through your diode / capacitor network when the MOSFET is off.  When you shorted the capacitors the generator worked against the small resistance of the diodes and the wires, slowing down a lot each MOSFET off interval.  That's why the motor ran slowly.  When you removed the short, the capacitors charged until a new equilibrium point was reached that balanced the power supply output energy each cycle against the electrical and mechanical losses.  Instead of heating the wires as with the short, much more of the power from the power supply went into mechanical work by spinning the motor faster against the friction in the system.  If you put a resistor or some other circuit that does work across the capacitor bank, then for the same power supply settings and MOSFET duty-cycle, the motor will slow down.

An experiment that you can do that I think is educational would be to put a fixed value power resistor, RSERIES, between the power supply and the motor.  Set the power supply to some fixed voltage with the current limit greater than:  ILIMIT >= VSUPPLY/RSERIES, and then vary the load across your capacitor, keeping track of the load resistance, load voltage, and motor speed.  See what load value gives the most total electrical plus mechanical power.

Free Energy | searching for free energy and discussing free energy


Offline TommeyLReed

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Re: Secret Of Back EMF
« Reply #2 on: August 13, 2014, 01:30:36 AM »
Hi Mark,

First of all there is no PWM involve in this design.

This works only off the RPM with a optical transistor  and 4 incoder on the disk at every 90deg.

The change in rpms is do to the fact BEMF is not running back to the coil.

The fee energy is coming from the BEMF of power input coil.

The motor speed up while the BEMF is collected, it slow down when shorted out and increase load.


Tom

Offline MarkE

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Re: Secret Of Back EMF
« Reply #3 on: August 13, 2014, 01:50:28 AM »
Hi Mark,

First of all there is no PWM involve in this design.

This works only off the RPM with a optical transistor  and 4 incoder on the disk at every 90deg.

In the video you showed a board connected to an optical interrupter switch that drives a MOSFET that chops the motor current.  And from your description above, the MSOFET chops the power supply connection to the motor. You are just using the rotation angle instead of a fixed frequency to drive the chopping / PWM.   Once the motor is going some relatively constant speed the MOSFET turns on and off at regular intervals and is for most intent and purpose acts same as a fixed frequency PWM chopper.
Quote

The change in rpms is do to the fact BEMF is not running back to the coil.
Actually, that is backwards.  The motor runs slowly when a lot of the energy built-up during the MOSFET ON time gets dumped into the external circuit during the MOSFET OFF time.  The motor runs its fastest when there is no external circuit other than the power supply.  Every last bit of energy that leaves the motor during a given MOSFET OFF interval gets replenished during the MOSFET ON time.
Quote

The fee energy is coming from the BEMF of power input coil.
If you measure carefully, you will find that there isn't any free energy.  All of the energy that can be accounted for in the external circuit and work performed by the motor spinning against the friction load and then some can be shown to come from the power supply.
Quote

The motor speed up while the BEMF is collected, it slow down when shorted out and increase load.
Absolutely, that is correct for the reasons stated above.
Quote


Tom


Offline tinman

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Re: Secret Of Back EMF
« Reply #4 on: August 13, 2014, 01:10:34 PM »
@ Tommey

First you need to know that it is not the backEMF you are collecting in your cap's-you are collecting the inductive kick back from the inductors within the motor when the mosfet opens.

BackEMF(counter EMF) dose the opposite to what you state,in that backEMF is what brings the motors current draw down-not raise it as you suggest. Back EMF is the voltage, or electromotive force, that pushes against the current which induces it.If there is no back EMF,the current draw will be very high.The more back EMF you have,the lower the current draw is

To explain a little better-Lets say you are supplying your motor with 10 volts @ 1 amp,and the voltage going to the inductors in your motor is very close to 10 volts. The backEMF (once the motor is up to running speed)may be say 7 volts.This means that the voltage across the inductors is only 3 volt's.So it is taking 10 volts @ 1 amp to maintain that 3 volt's across the inductors of the motor. If there was no back EMF,then the voltage across the same inductors will be very close to 10 volt's,and it would take a lot more amp's(current) to maintain that 10 volts across the inductors.A simple way to see this is when you first start an electric motor,and there is very little backEMF.You will see a high current draw(start up current)-same as when you place an electric motor under load.

So back EMF is needed to bring current draw down-it dosnt raise the current draw of an electric motor.

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #4 on: August 13, 2014, 01:10:34 PM »
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Offline TommeyLReed

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Re: Secret Of Back EMF
« Reply #5 on: August 13, 2014, 05:02:58 PM »
Hi Tinman,

 I built many motors and even have 19hp DC motor. BEMF it created due to starting a motor under load. When motor speed is full speed, less if any BEMF is created.

The reason speed controller fail is the increase of BEMF when motor are at the stall point.

I can also prove this with a transformer load using DC pulse. This way you just might understand how BEMF really works.

This is what BEMF does using a coil to recover BEMF. This motor is being power by BEMF only!

https://www.youtube.com/watch?v=2xLwBaub4lc&list=UUp3mD3EJromKns3YpglKdpA


Tom.

Offline TommeyLReed

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Re: Secret Of Back EMF
« Reply #6 on: August 13, 2014, 06:44:37 PM »
Hello all,

If you think Back EMF is not something special, look what happens when you use a transformer and DC pulse.

https://www.youtube.com/watch?v=Ty5CLgjmd4c

Tom

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #6 on: August 13, 2014, 06:44:37 PM »
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Offline MarkE

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Re: Secret Of Back EMF
« Reply #7 on: August 13, 2014, 07:42:53 PM »
Tom, Tinman is correct.  Take a small DC motor such as from a toy.  Measure the winding resistance with a DMM.  Then hook the motor up to a power supply with a current sense.  Lock the rotor.  turn on the power supply to a low voltage and measure the current.  It will be V/R.  Unlock the rotor and as the motor comes up to speed the current goes down.  The net current through the motor is:  I=(VSUPPLY - w*KGENERATOR)/RWINDING.  Since the motor torque is:  I*KTORQUE = (VSUPPLY - w*KGENERATOR)/RWINDING*KTORQUE

Offline TommeyLReed

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Re: Secret Of Back EMF
« Reply #8 on: August 13, 2014, 09:11:54 PM »
Hi Mark,

Clearly you don't understand my test, I know that. I was showing the effect of the diode when it cancels out the BEMF by grounding it..

As I place the diode in the motor, the BEMF is shorted out, this increase load while slowing down the motor a little.

When I take the diode out and feed the bemf into the capacitors the motor increasee with speed and load drops, that was my point of this test.

This test show the grounding out BEMF with a diode on the +/- create a greater load then without it.

That was my point on the video!

Tom.


Offline MarkE

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Re: Secret Of Back EMF
« Reply #9 on: August 13, 2014, 09:47:30 PM »
Hi Mark,

Clearly you don't understand my test, I know that. I was showing the effect of the diode when it cancels out the BEMF by grounding it..

As I place the diode in the motor, the BEMF is shorted out, this increase load while slowing down the motor a little.

When I take the diode out and feed the bemf into the capacitors the motor increasee with speed and load drops, that was my point of this test.

This test show the grounding out BEMF with a diode on the +/- create a greater load then without it.

That was my point on the video!

Tom.
Tom, there are two sources of BEMF in a motor:  BEMF induced by motion which is the generator BEMF, (flux changes across the conductors), and BEMF caused by changes in the current path to the motor windings.  When you switch your MOSFET ON or OFF the latter is at work.  When the MOSFET turns ON the current in the motor windings does not change instantly.  The motor winding inductance produces a BEMF in response to applied voltage changes that decays with time.  The current changes from its previous value following an inverse exponential towards a limit value of the difference between the power supply voltage and generator BEMF divided by the winding and circuit resistance.  When the MOSFET switches OFF inductor BEMF develops to maintain the winding current.  When it builds high enough your diode conducts and curent continues into your capacitor and whatever you have connected across it.  If the voltage on the cathode side of your diode is less than the generator BEMF, then current builds-up towards a limiting value of: (w*KGENERATOR-VDIODE-VCAPACITOR)/RCIRCUIT.  When you remove the short across the capacitor, the capacitor ultimately charges to the point that it does not load the generator BEMF.

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #9 on: August 13, 2014, 09:47:30 PM »
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Offline SeaMonkey

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Re: Secret Of Back EMF
« Reply #10 on: August 13, 2014, 09:57:13 PM »
Rather than "shorting" the input to the capacitors,
why not disconnect the capacitors instead?

By shorting the kickback the magnetic field which
is producing it is prolonged within the motor.  It
may be that is what is reducing the motor speed and
causing a higher than normal current flow.

In some pulse operated motors a diode is placed
across the motor leads to "short" the kickback
which actually increases motor efficiency by
prolonging the current produced magnetic field.

Offline forest

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Re: Secret Of Back EMF
« Reply #11 on: August 14, 2014, 12:40:49 PM »
Ok. I really WANT somebody experienced to clear the difference and explain this topic.
For my simple mind there are two effects in play : let's call the first one " backEMF" rather COUNTER-EMF and the second one rather FLYBACK SPIKE. Am I right ?
CounterEMF is what I see as effect of self-inductance motors coils and I heard it limits the voltage applied to motor coils, because it is in oposite to applied power source voltage polarity.

Is this is correct then :

1. How is that everytime it fights against applied power ? Is that a matter of  arrangements of coil ?
2. What would happen if counterEMF in motor coils will be very small ? Would that burn out wires inside motor ?


Offline MarkE

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Re: Secret Of Back EMF
« Reply #12 on: August 14, 2014, 01:45:32 PM »
Hopefully this diagram will clear things up.

Offline tinman

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Re: Secret Of Back EMF
« Reply #13 on: August 14, 2014, 03:36:17 PM »
Ok. I really WANT somebody experienced to clear the difference and explain this topic.
For my simple mind there are two effects in play : let's call the first one " backEMF" rather COUNTER-EMF and the second one rather FLYBACK SPIKE. Am I right ?
CounterEMF is what I see as effect of self-inductance motors coils and I heard it limits the voltage applied to motor coils, because it is in oposite to applied power source voltage polarity.

Is this is correct then :

1. How is that everytime it fights against applied power ? Is that a matter of  arrangements of coil ?
2. What would happen if counterEMF in motor coils will be very small ? Would that burn out wires inside motor ?
BackEMF(counter EMF) limits the voltage in the motor coils(as you call them forest),and thus limits the current. The lower the Back EMF,the higher the current draw.

Inductive kickback(or fly back) is when a powered inductor has it's power source cut off quickly(becomes open circuit).The current wants to maintain its flow as the magnetic field around the inductor collapses. Now while the voltage potential inverts from powered to non powered across the inductor,the current flow remains in the same direction. This is the very reason the Bendini ssg has the charge battery negative hooked to the run battery positive,as the positive becomes the negative potential when the inductor becomes open(transistor becomes open).

From what i can make out in Tommeys setup(a bit hard without a schematic),is the reason the motor bogs down when he shorts out the caps,is because he has created a continual loop in the motors inductors(coils).This being the case,the current has no where to go but back into the coils,and this would maintain the magnetic field around the coils,and in turn would be what is bogging the motor down,and drawing the extra current. Inductive kickback(fly back) is not free energy,but is what is left over from the supplied power that the motor(and all its losses) didnt use(convert).

Free Energy | searching for free energy and discussing free energy


Offline tinman

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Re: Secret Of Back EMF
« Reply #14 on: August 14, 2014, 03:49:45 PM »
Hello all,

If you think Back EMF is not something special, look what happens when you use a transformer and DC pulse.

https://www.youtube.com/watch?v=Ty5CLgjmd4c

Tom
Tom-you made an inverter.
And it's inductive kick back or fly back-not back EMF.

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #14 on: August 14, 2014, 03:49:45 PM »

 

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