[TowerTalk] Reply - KW3000 with 1/2 inch Drill Motor - Wrongassumption in responses

[jimlux]

Dubovsky, George wrote:
> You will still lose torque with a pwm light dimmer. You will need something like an variable speed drive, where you vary the drive frequency and voltage simultaneously, essentially synthesizing a complete sine wave at an adjustable frequency. I use them on three-phase motors on my lathe and mill, but they are also available for single-phase motors. Not cheap, but less than the Hole Hawg ;-)
> 
> 73,
> 
>

I noticed in one of the trade rags recently (I can't recall which) that 
you can get single phase in, 3 phase out, variable frequency drives for 
small motors in the $100 range.  They're not the totally fancy vector 
drives that use the backemf to measure torque and stuff, just a straight 
V/Hz sort of drive, but still.. pretty nifty.

I would think, though, that the HoleHawg is a standard brushed universal 
motor.. a light dimmer type control might work fairly well.. It's just 
going to be highly nonlinear, and the triggering erratic UNLESS you put 
a resistive load in parallel with the motor. Something like a 25W-100W 
light bulb works well.  The problem with driving an inductive load is 
that the RC/diac phase control scheme for the triac doesn't switch very 
well because the load current and voltage are out of phase.

If you have a phase control dimmer that uses two back to back SCRs, 
rather than a triac, it will also work better.