Stepper motor coil resistance. What is an acceptable value?

[gavztheouch]

Thanks Robin,

Does that mean the resistance has no contribution towards causing a voltage spike? What are the common causes of blown MOSFET's.

[Robin Hewitt]

What are the common causes of blown MOSFET's.

MOSFET's have a break down Voltage which does not want to be exceeded.

The fix for inductance is diodes strategically placed so the current in a coil always has an escape route.

MOSFET's usually have a reverse diode fitted. If not it must an external component and it needs to be fast switching.

Consider this...

A MOSFET says, "I now want the current to flow clockwise through this coil".
The coil replies, "Bad luck mush, my inductance says we are still going counter clockwise, get used to it".
The protection diodes say, "Panic not, we will allow the current to flow".

Basically, both ends of every motor coil can draw power off the ground rail or add power to the voltage rail through the protection diodes.

Now you have to ask yourself:-
- Are the protection diodes fitted?
- Are they fast enough to protect my MOSFET's?
- Can my power supply handle this sudden reversal without going way over Voltage? Can it sink as well as source?