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Author Topic: Secret Of Back EMF  (Read 37653 times)

Offline TommeyLReed

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Re: Secret Of Back EMF
« Reply #15 on: August 14, 2014, 04:14:44 PM »
Hi All,

This is the basic design on the video.

This version replace the motor with a transformer.

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

Tom

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Re: Secret Of Back EMF
« Reply #15 on: August 14, 2014, 04:14:44 PM »

Offline MarkE

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Re: Secret Of Back EMF
« Reply #16 on: August 15, 2014, 12:01:38 AM »
Tom, here is your drawing with some annotations that should explain things.

Offline TommeyLReed

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Re: Secret Of Back EMF
« Reply #17 on: August 15, 2014, 01:35:16 AM »
Hi Mark,

Yes that is the design, I did it in a simple drawing.

Now the question is, do you still think this is not BEMF?

As you ground out the capacitor, the two diodes run in series to positive and negative post of the coil, this shorts out the BEMF when kick back happens.

Like many transformer using dc pulse this is needed to protect the transister from being destroy from BEMF high voltage spikes.

My other question is why would the motor slow down, when I just short out the BEMF?

I believe it's from a negative pulse that pulls the motor magnet field backwards.

Question anyone?

Tom




Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #17 on: August 15, 2014, 01:35:16 AM »
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Offline MarkE

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Re: Secret Of Back EMF
« Reply #18 on: August 15, 2014, 01:45:21 AM »
Hi Mark,

Yes that is the design, I did it in a simple drawing.

Now the question is, do you still think this is not BEMF?

As you ground out the capacitor, the two diodes run in series to positive and negative post of the coil, this shorts out the BEMF when kick back happens.

Like many transformer using dc pulse this is needed to protect the transister from being destroy from BEMF high voltage spikes.

My other question is why would the motor slow down, when I just short out the BEMF?

I believe it's from a negative pulse that pulls the motor magnet field backwards.

Question anyone?

Tom
Tom, nothing has changed.  The capacitor shorted or not provides a path for the magnetizing energy in the motor winding when the path through the MOSFET opens.  The capacitor charges cycle by cycle until the leakage through the capacitor and the diodes is enough to dissipate the magnetizing energy dumped into the capacitor each cycle.  When the switch is closed, the energy dissipates much more slowly than when the capacitor is charged up to some voltage.  That means that when the switch is closed more energy goes to the motor and it has more torque.  If the motor is slowing down with the switch closed, then the diodes to the capacitor are leaking badly.  In that case, generator EMF is driving durrent through the leaking diodes and switch.

Offline tinman

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Re: Secret Of Back EMF
« Reply #19 on: August 15, 2014, 06:53:59 AM »
 ;)
Tom, nothing has changed.  The capacitor shorted or not provides a path for the magnetizing energy in the motor winding when the path through the MOSFET opens.  The capacitor charges cycle by cycle until the leakage through the capacitor and the diodes is enough to dissipate the magnetizing energy dumped into the capacitor each cycle.  When the switch is closed, the energy dissipates much more slowly than when the capacitor is charged up to some voltage.  That means that when the switch is closed more energy goes to the motor and it has more torque.  If the motor is slowing down with the switch closed, then the diodes to the capacitor are leaking badly.  In that case, generator EMF is driving durrent through the leaking diodes and switch.
;)

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #19 on: August 15, 2014, 06:53:59 AM »
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Offline MarkE

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Re: Secret Of Back EMF
« Reply #20 on: August 15, 2014, 07:58:45 AM »
Hi Mark,

Yes that is the design, I did it in a simple drawing.

Now the question is, do you still think this is not BEMF?

As you ground out the capacitor, the two diodes run in series to positive and negative post of the coil, this shorts out the BEMF when kick back happens.

Like many transformer using dc pulse this is needed to protect the transister from being destroy from BEMF high voltage spikes.

My other question is why would the motor slow down, when I just short out the BEMF?

I believe it's from a negative pulse that pulls the motor magnet field backwards.

Question anyone?

Tom
Tom, you can approximate shorting out the motor by for example putting a really good diode across it.  The BEMF then takes on a low value as it only has to rise enough to make the diode forward conduct.  That gives the motor the highest average torque during the MOSFET off interval.  The higher the voltage that is across the motor:  D1 anode to D3 cathode, IE the greater the BEMF, the faster that current in the motor winding decays, the lower the average torque, and the slower the motor runs against any constant load compared to the "shorted" condition.  If the motor is slowing down when you close the switch, then that means that you are diverting power when the MOSFET is on due to leaky D1 and D3 diodes.

Dave45

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Re: Secret Of Back EMF
« Reply #21 on: August 15, 2014, 12:52:58 PM »
Tom have you tried to recycle the kick back

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #21 on: August 15, 2014, 12:52:58 PM »
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Offline forest

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Re: Secret Of Back EMF
« Reply #22 on: August 15, 2014, 05:55:59 PM »
First,could you resize down images ?

I see that you all state that backEMF during coils magnetizing current (mosfet ON) is the same backEMF which charge capacitor bank.Am I right ?

I , oppositely think it is two different effects. First is due to self-inductance of motor coils , second one is due the LC oscillations between self-inductance of coils and distributed capacitance of wires.Because voltage is rised expotencially in short time it looks like a spike called flyback spike, but in fact it is ringing down oscillation.

What do you think ?

Offline MarkE

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Re: Secret Of Back EMF
« Reply #23 on: August 16, 2014, 01:53:31 AM »
Forest, if you are addressing me, I use a 72dpi resolution  which is OK for 12 point type and for B size pictures stays below the 1280 pixels that Stefan asks.  The image file sizes are generally well under 100Kbytes.  The alternatives are breaking up the pictures or making them fuzzy.

Because only one of the switches is active, only the magnetizing energy, IE energy stored as I2LWINDING/2 goes through the D1/capacitor or switch/D3 path.  That energy builds-up when the MOSFET is ON and discharges when the MOSFET turns OFF.

The energy that is stored in the winding capacitance and other parasitics is next to nil compared to the magnetizing energy, and can be safely ignored with no loss in accuracy.  Ringing can be seen when the magnetizing inductance gets completely discharged. Then the very small remaining energy can slosh back and forth between the inductance and capacitance.

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #23 on: August 16, 2014, 01:53:31 AM »
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Offline MarkE

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Re: Secret Of Back EMF
« Reply #24 on: August 16, 2014, 02:12:57 AM »
Tom have you tried to recycle the kick back
Dave, in order to recycle the magnetizing energy back into the power supply an active switch is needed on both sides of the motor.

Offline tinman

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Re: Secret Of Back EMF
« Reply #25 on: August 16, 2014, 02:21:47 AM »
First,could you resize down images ?

I see that you all state that backEMF during coils magnetizing current (mosfet ON) is the same backEMF which charge capacitor bank.Am I right ?

I , oppositely think it is two different effects. First is due to self-inductance of motor coils , second one is due the LC oscillations between self-inductance of coils and distributed capacitance of wires.Because voltage is rised expotencially in short time it looks like a spike called flyback spike, but in fact it is ringing down oscillation.

What do you think ?
No-the only one that claims this is Tommy.

What charges the caps is the collapsing magnetic field around the inductor,when the mosfet becomes open. When you have a low resistive load placed on the inductive kickback,the magnetic field collapses slowly(motor bogs down),when you have a high resistive load,the magnetic field collapses much more quickly(caps have high internal resistance)-motor dosnt bog down so much.

The simple SSG pulse motor is a good learning tool,and you can see all this happen on a scope when you place different resistive loads on the kickback output.

Free Energy | searching for free energy and discussing free energy

Re: Secret Of Back EMF
« Reply #25 on: August 16, 2014, 02:21:47 AM »
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Offline TommeyLReed

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Re: Secret Of Back EMF
« Reply #26 on: August 16, 2014, 02:36:41 AM »
Hi TinMan,

Please explain where the high voltage comes from?

If this is a simple load on the motor then why would the caps reach 50v-100v?

Tom

Offline tinman

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Re: Secret Of Back EMF
« Reply #27 on: August 16, 2014, 03:34:59 AM »
Hi TinMan,

Please explain where the high voltage comes from?

If this is a simple load on the motor then why would the caps reach 50v-100v?

Tom
Hi Tom
I am glad you asked,as the answer will show you why it isnt the backEMF you are collecting. The back EMF voltage is always less than the supplied voltage to the coil(coils) in the motor. I think you were supplying 19 volts from your power supply?,so the back EMF voltage would be less than that. This means that the 50-100 volts in your cap could not be from the back EMF.

When you power up an inductor(coil),a magnetic field is built around the inductor(this im sure you know).When the power flowing into the inductor is abruptly disconected(mosfet opens),the magnetic field around the inductor collapses.The speed that this field collapses is directly related to the load applied to the inductive output-(in your case,caps),and the voltage produced by the inductive kickback is directly related on how fast that field can collap's. So if you have a very low resistive load on the kickback output(say 10 ohms),then the maximum voltage reached may only be say 12 volts across that 10 ohm's-but the current will be high and flow for longer period of time, due to the magnetic field collapsing slower. If you have say a 100 ohm load on the inductive kickback output,then your voltage across that 100 ohm load may be 70 volts,but the current flow will be lower,and for a shorter period of time,because the magnetic field collapses faster.

As your caps have a high resistance value in your setup,you can achieve a high voltage from the inductive kickback.If you place a 10 ohm resistor across your cap's,the voltage will drop,but the current will rise,and your motor will bog down.
Look at your inductive kickback as a generator hooked to a motor-the only difference in your case ,is that the generator and motor are all one device. But as you load the generator with heaver loaed's,you will see your motor bog down-just as in a nomal generator/motor system.

If you like,i can take the time to build a pulse motor,and make a video showing you on a scope how all this happens.

Offline MarkE

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Re: Secret Of Back EMF
« Reply #28 on: August 16, 2014, 03:40:33 AM »
Hi TinMan,

Please explain where the high voltage comes from?

If this is a simple load on the motor then why would the caps reach 50v-100v?

Tom
Tom the energy that builds up in the motor magnetizing inductance has to be dissipated.  The capacitor alone stores energy with little dissipation.  Voltage builds up until something gives: the capacitor and/or the diodes so that the magnetizing energy gets dissipated each cycle.

Offline MarkE

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Re: Secret Of Back EMF
« Reply #29 on: August 16, 2014, 03:44:58 AM »
Hi Tom
I am glad you asked,as the answer will show you why it isnt the backEMF you are collecting. The back EMF voltage is always less than the supplied voltage to the coil(coils) in the motor. I think you were supplying 19 volts from your power supply?,so the back EMF voltage would be less than that. This means that the 50-100 volts in your cap could not be from the back EMF.

When you power up an inductor(coil),a magnetic field is built around the inductor(this im sure you know).When the power flowing into the inductor is abruptly disconected(mosfet opens),the magnetic field around the inductor collapses.The speed that this field collapses is directly related to the load applied to the inductive output-(in your case,caps),and the voltage produced by the inductive kickback is directly related on how fast that field can collap's. So if you have a very low resistive load on the kickback output(say 10 ohms),then the maximum voltage reached may only be say 12 volts across that 10 ohm's-but the current will be high and flow for longer period of time, due to the magnetic field collapsing slower. If you have say a 100 ohm load on the inductive kickback output,then your voltage across that 100 ohm load may be 70 volts,but the current flow will be lower,and for a shorter period of time,because the magnetic field collapses faster.

As your caps have a high resistance value in your setup,you can achieve a high voltage from the inductive kickback.If you place a 10 ohm resistor across your cap's,the voltage will drop,but the current will rise,and your motor will bog down.
Look at your inductive kickback as a generator hooked to a motor-the only difference in your case ,is that the generator and motor are all one device. But as you load the generator with heaver loaed's,you will see your motor bog down-just as in a nomal generator/motor system.

If you like,i can take the time to build a pulse motor,and make a video showing you on a scope how all this happens.
The generator BEMF is always less than the supply voltage.  The motor winding BEMF is a flyback voltage limited only by the external circuit and the breakdown voltage within the motor.  Recirculating the motor winding energy speeds the motor up by supplying more average current and therefore torque.  As there is no specific DC current path provided for the winding energy, the capacitor charges up until something starts leaking badly.

 

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