When a low voltage DC motor is running and then disconnected at its terminals and it has no fly back diode, usually I would see sparks across the wire and the motor.

My questions are:
1) Are these sparks the result of the DC motor being an inductive device?
2) Are they avoided with a "flyback" diode?
3) Are these sparks high voltage sparks (read it takes thousands of volts to break down the ions in the air?)

 

The sparks are due to the DC being generated by any P.M. DC motor that is revolving.
The voltage is directly related to rpm and is the same polarity as the applied voltage.
Max.

 

Would a diode prevent the sparks?

 

The back EMF or the same-polarity generated voltage is necessary to offset or oppose the applied voltage in order to reduce the otherwise excessive current at full voltage.
Is this just a momentary effect you see or constant?
Max.

 

Thanks for responding again.
I read somewhere the diodes can and should sometimes be used with motors.
Momentary effect.

 

They are often used in switching applications, not so much in linear control.
Care has to be taken if switching bi-directional.
Max.

 

Ok. Are they used in switching applications because of the inductance effect? Is that what causes the sparks? Would the diodes prevent the sparks?