Powering A Grinding Spindle With A DC Motor.

[JimDawson]

Hi Bob, no worries about the thread the question suits the spirit of it, and it's interesting, could you please tell me what you mean by "cogging"
When I looked it up it said "Cogging means that when you turn the motor by hand it jumps from one magnet pole to the next and feels bumpy when you turn it" but I'm thinking you might mean something about how it running.

Pretty much the same thing applies when running at very low RPM, This is where the commutation comes into play from the controller when connected to the Hall sensor. This effect should go away as the speed comes up a bit. The internals of a BLDC motor look somewhat like a stepper motor.

 

[frostheave]

Hi Bob, no worries about the thread the question suits the spirit of it, and it's interesting, could you please tell me what you mean by "cogging"
When I looked it up it said "Cogging means that when you turn the motor by hand it jumps from one magnet pole to the next and feels bumpy when you turn it" but I'm thinking you might mean something about how it running.

Hi Don,
What I mean by cogging is, instead of the motor turning smoothly at a constant rpm, the speed varies, mostly at low rpm. The thing is, it does not vary consistently, like once every second. It happens at an inconsistent and seemingly random rate. I know this is happening because of the sound the mill makes. I can hear the speed changes as the pitch of the sound varies. The problem is compounded because the quality of the gear meshing isn't great, i.e. the gearbox has a lot of slop. This results in a VERY noisy mill that is no fun to use.

I talked to the Optimum tech and he said the problems I am experiencing are due to a poor motor driver design and the sloppy meshing of gears in the gearbox. Short of a belt drive, I can't do much about the gearbox. With the realization my BLDC motor can be run with a VFD, thanks to Jim Dawson, I want to see if the VFD makes a significant difference. Maybe with a proper motor driver the mill will quiet down. I will report back with my findings.

Bob

 

[JimDawson]

I had a chance to play with a small (about 400 Watt) BLDC motor a couple of days ago. This particular one is powering an electric bicycle, 36 volt power.

What I found was that it didn't seem to make any difference if the Hall sensor was connected to the controller or not. It seem to run just the same, and was smooth running throughout its speed range. In this case the operator is providing the feedback for speed control. From this I think I can conclude that running a BLDC motor with a VFD should work well, but I still haven't had a chance to actually try it.