Both the variac/autotransformer and the HF triac-diac-Router Speed Control
methods of variable speed will exhibit significant motor power loss at
reduced speed settings.
FWIW vari-speed AC corded drills have used PWM circuits in the
trigger-switch speed controls, and operate well with only 2-wire connections
to the motor (no external feedback component required), when SCR speed
control circuits contain a low value series "sense" resistor in their
circuitry.
Some DC motor vari-speed control modules from several manufacturers have
selectable sense resistor recommendations for using a specific controller
model number with different HP size motors.. the resistor value selected is
different if using a 1/4 HP or a 1/2 HP motor when utilizing the same model
of controller.
I haven't had any of the newer drill trigger/speed circuits apart recently
to verify if PWM controller circuits are still being used, but they likely
are, as a commonly used circuit design generally gets cheaper to produce as
millions more are manufactured.
Without using PWM for speed control, most drills would be
problematic/useless at reduced output torque when used at lower speeds.
--
WB
.........
"DoN. Nichols" <
BPdnic...@d-and-d.com> wrote in message
news:slrnjkog81.42...@Katana.d-and-d.com...
>
> Well ... since it is a universal motor, cheapest way (not the
> best) is to plug it into a Variac (if you have one) and turn the voltage
> down. You won't get really steady speed with anything, however, unless
> you get really fancy with a controller which produces PWM power and
> monitors the back EMF (to measure the speed) between pulses. That would
> probably require a replacement power cord to get the voltage sensing
> close to the motor and separate from the voltage drop in the power cord.
>