Erl-1340

pstemari said:
As I understand it, getting flat torque on a real-world induction motor at low frequency is tricky because you aren't inducing current in the armature to the extent you would at higher frequency.
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I think you are referring to is called cogging, and everything I have read says it becomes a real problem around 5hz, unless you get into real high dollar stuff.
 
I don't know the particulars, but when setting up my VFD on my mill there was a constant torque mode that I enabled. So far, I've had all the torque I needed. And I do a fair amount of milling down around 20-30 Hz.
 
IIRC cogging is when the armature slips and doesn't make it to the next pole on the stator, similar to losing steps on a stepper motor.

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wrmiller said:
I don't know the particulars, but when setting up my VFD on my mill there was a constant torque mode that I enabled. So far, I've had all the torque I needed. And I do a fair amount of milling down around 20-30 Hz.
Click to expand...

20-30hz is well into the safe zone, it's when you get down into the single digit range that stuff starts to get dicey.
 
Got some photos from Matt of my machine. Should be on its way from Pittsburgh to Renton now.
Pittsburgh1.jpg
Pittsburgh2.jpg
Pittsburgh3.jpg
 
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