Secret Of Back EMF

[TommeyLReed]

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

[MarkE]

Tom, here is your drawing with some annotations that should explain things.

[TommeyLReed]

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

[MarkE]

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.

[tinman]

 

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.