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Old 08-19-2015, 04:18 AM
bistander bistander is online now
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Join Date: Apr 2015
Posts: 1,587
armature field

Originally Posted by vidbid View Post
Just reporting on a Video.

Electric OU: Coil Shorting Shunt Motor 2: Effect of Diode - YouTube

Okay, people, what is your explanation for this effect?
Slightly more interesting than the first one. Here the armature in the unexcited stator field does produce a flux with the armature current. When stationary there is a net zero flux through the stator and therefore no torque hence no rotation. When twisted by hand the armature flux becomes distorted in the field (stator) structure and establishes a flux field to interact with the armature current and produces torque, hence rotation is sustained. This armature induced flux is weak compared to the main field flux one would have with an excited field and so the torque in this mode is barely enough to maintain rotation at no load.

The effects from shorting the field and doing so with a diode, I suspect, is aiding or hindering this weak armature field by establishing a current in the field coils due to a transformer effect. The diode rectifies the induced AC in the coil. One polarity of armature excitation, that aids or increases flux and produces more torque causing acceleration and reduced current (higher BEMF). The other polarity, it reduces the flux, torque is lost, nearly stalls and current increases.

Putting a scope on it would verify that.

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