Stepper motor holding torque without coils energized?

Question

I want to know what torque a stepper motor can hold when stationary. They seem to only have one figure in specifications for holding torque which, I presume, is while coils are energised.

How is this normally handled in usage of stepper motors? Is there a way of calculating holding torque while coils are not energised? I know braking can be done by shorting the coils, but it's obviously not as effective as just holding one coil energised to maintain position. Is one coil usually just kept energised to hold position with maximum torque? Is there a limit to how long one coil can remain energised?

Answer 1

The value Detent Torque or Cogging Torque is what you should look for in the specification sheet. The detent torque is related to stepper motor power loss. The following is a reference from Minebea' web site.

Detent Torque: amount of torque that the motor produces when it is not energized. No current is flowing through the windings.

Here is an excerpt from 57BYGH420 Stepper Motor Datasheet

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Referances:

• Cogging torque
• Stepper Motor Speed and Torque Relationship
• In-depth Learning of Cogging/Detenting Torque through Experiments and Simulations
• Step Motor Basics Guide