12 Volt power Supply

It sounds like you are talking about AC induction motors. The energy transfer mechanism from stator to rotor in those gets very inefficient when the motor is stalled, and they generate a large amount of heat (relative to the torque produced). But DC motors happily stall with reasonable rate of temperature rise, as long as the current is limited to no more than full rated. The only thing that will get very hot is the big resistor limiting the current.

For A DC motor it is. Full load current will produce full load torque, whether the motor is standing still or running at full speed.

For AC induction motors, the ratio can be higher than that, depending on the class of the motor. For DC (permanent magnet) motors the locked rotor current is the voltage divided by the armature resistance.

If full load torque will turn the motor and load from a stand still, then full load current will turn it, since it produces that torque. There is a very different story for AC induction motors.

Not if the current is externally limited, and that is the point of this exercise.

The O.P. asked about testing motors. That implies somebody is testing them (watching the test). If the motor doesn't start, it has failed the test. But he wants to preserve the test power supply from higher than normal current during that occurrence (and for the brief instant it takes good motors to get moving).

How much worse would it be, if the motor could not turn, from some external mechanical problem, if the current was not externally limited, but went all the way to V(supply)/R(armature)? I think a smoking resistor is better than a smoking motor or smoking diodes or smoking transformer.

Thanks! Now I see I had it completey wrong. I appreciate the corrections.

Yup. All I could see was a bunch of responses that were intended to protect the diode at the expense of the motor, and I'd rather blow the diode than the motor.

Ed