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Bob Engelhardt

On 11/4/2019 12:33 PM, wrote:
Keep in mind that the Kleig Light (Carbon-arc) and mercury-vapor lamps, some of which are dimmable to a point, are reactive loads. And, the Kleig light as stage lighting persisted into the 1970s on movie sets (with proper filtering against dangerous actinic wavelengths) and mercury-vapor devices are still used in some lighting designs. So, if a lighting device required a strike function, and repetitive in some cases, that would certainly de-rate the Variac as compared to a simple incandescent/resistive load.

I never would have thought of them as reactive, but it's interesting.

Note also that brush-type AC motors may have variable speed controls - such as on your corded hand-drill. I can think of any number of devices that would use such a motor and also allow for the use of a large Variac. A theatrical variable wind machine comes immediately to mind.

My limited experience with single-speed universal (brushed) motors is
that reducing the voltage reduced the speed, but also the torque. To an
extent that it was not useful.