On Dec 6, 9:11*am, "Existential Angst"
wrote:

Universal motors (with brushes) can be speed-controlled with a triac
or SCR, with some care; that's how the variable-speed Dremel works.

What do you think of the Dart controller in the graingers link?
What method does it use? *It's sposedly good up to 2.5 A, which on paper is
about 1/3 hp.

Intended for universal motors; this is a triac or SCR type, it always
puts out
the same as line frequency but at lower average voltage. The high
end of the current range would only apply to motors of the universal
type, with brushes, and it loses torque at low speed. It's just a
Variac-substitute (as the Variac functions, so will this).

I put the variac back on this blower, on my bench.
The variac actually does an OK job, but speed regulation is not very stable,

The variac and the Dart controller both work on a shaded-pole motor
by running the voltage low enough to partially stall the motor; that
means
the rotor is demagnetizing and generating eddy currents. The rotor
gets HOT when that happens, it's only recommended if the motor was
designed for it (like the multispeed range hood fan motors one often
sees).
No high power motors are designed for that kind of use.