I'm getting conflicted information about this so why not ask here.

To clarify beforehand: Under DC motor I understand a motor with 2 terminals where you apply DC voltage to get current flowing in 1 direction(some people use DC to describe 3-phase brushless motors) With AC motors I understand n-phase brushless motors with n amount of terminals where you apply a AC voltage in different phases on the different pairs of terminals.

I also know for a fact that mechanical resistance is proportional to electrical resistance so it's gets even more confusing knowing this.

Now for the actual question: I know that a type of motor can get damaged if stalled. I've also read that current is minimal when a certain other type of motor is stalled. Can I get a explanation which one is which and why?

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    \$\begingroup\$ "I also know for a fact that mechanical resistance is proportional to electrical resistance " Wrong. Electrical resistance is simply a property of the circuit (wire, brushes, leads, terminals). Mechanical resistance is to do with bearing construction (how easy it turns). If you actually mean torque this is a function of current. Current depends upon conductance (the inverse of resistance), the speed of rotation (back emf) and the applied voltage. \$\endgroup\$ – JIm Dearden Oct 25 '16 at 12:04
  • \$\begingroup\$ Jim, in the asynchronous AC motor equivalent circuit, mechanical resistance (counter torque) increases the electrical rotor resistance. I think that's what the OP meant. \$\endgroup\$ – Janka Oct 25 '16 at 12:49

Damaging a motor through stalling it happens because of overcurrent, and overheating from that.

Brushed DC motors for example don't like stalling because they rely on the turn speed for both creating a Counter EMF voltage and for the rotating frequency to make their rotor inductance present an additional resistance to the circuit. Accounting both, the current is highest when stalled.

But e.g. some AC asynchronous motors don't rely much on rotor inductance for building an additional resistance in the circuit and don't have an EMF voltage at all. Instead, they have their highest current (and torque) at about 80% of the rated speed. So it's unlikely you can overcurrent them by stalling. Still they may overheat by stalling because their cooling fan does not rotate.


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