why torque motor does not overheat if stalled for very long,
could some explain how. If used in servo mechanisms where cooling(nature or forced) in nearly impractical.
Electronic – why torque motor doesn’t overheat if stalled for very long
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The increase in torque can be explained by the following physical relationships:
The Torque that develops in a motor comes from the interaction between the stater's and rotor's magnetic fields.
The strength of each magnetic field is proportional to the current flowing through the stater and rotor.
The magnetic field of the rotor will attempt to align with the magnetic field of the stater(South to North and North to South), this is where the turning force exerted between the rotor and stater comes from.
Therefore if you push more current through the rotor a stronger magnetic field is developed and a greater turning force is exerted from the interaction of those magnetic fields. This concept is more simply illustrated by looking at a brushed DC motor. Picture below from: https://www.globalspec.com/reference/10791/179909/chapter-3-ac-and-dc-motors-ac-motors-ac-induction-motor
Hope this Helps!
In a nutshell for a PMDC motor:
- voltage = speed
- current = torque
Note that for a given voltage there is a speed at which there is (almost) no current going through the rotor, because of back emf (the rotor is inside a magnetic field generating a counter-emf on the brush inputs). To get more torque at that speed you have to increase the voltage (and basically overdrive the motor, leading to early failure).
There are a whole bunch of other factors that can come into play such as mechanical resonances at certain speeds, etc.
Regarding the startup problem you had/have- is it repeatable or did it just happen the first time? It could have been a poor brush contact, etc.
Gory details:
Best Answer
A torque motor is designed to be run at stall. Maintaining torque at a fixed shaft position is exactly how you expect it to be run.
The motor is designed so that its thermal characteristics allow this operation. The windings are relatively thick, so the Joule heating is minimized, and the case construction allows good transfer of internal heat to the surrounding structure. The windings are normally located far from the shaft axis, so that the product of magnetic force and radius of action (torque) is maximized. This in turn means that the windings are well-coupled thermally to the case, and there is relatively little heat dissipated deep within the motor.