DC Motor Sparks

[geratheg]

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 diode?
3) Are these sparks high voltage sparks (read it takes thousands of volts to break down the ions in the air?)

[jeristair]

The sparks are because the motor appears (from an electrical view) as an inductor.
Turning off the motor causes the current to suddenly stop, therefore the inductor will create a large back emf

[Seekonk]

Yes
Not necessarily
It doesn't take thousands.  Arc welders work at about 35V.  You should pick up a copy of GASEOUS CONDUCTORS, the bible of things that go arc in the night by James Dillon Cobine.

[macboy]

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 diode?
3) Are these sparks high voltage sparks (read it takes thousands of volts to break down the ions in the air?)

1. Yes
2. No, you use capacitors across the motor terminals to prevent the sparking. A snubber may be better (some series resistance as either ESR of the cap, or added as a resistor), but a simple capacitor will do. Often two small caps are used, one from each terminal to the motor can.
3. Yes, suddenly interrupting current to an inductor such as a motor coil will produce a "high" voltage spark. How "high" the voltage is will depend on how much is needed to generate the spark (distance to the conductor).

[geratheg]

A flyback diode won't prevent the sparks? Would the diode just short the terminals of the motor in one direction thus preventing the sparks?