"Peter A" > wrote in message
...

-snip-

> Microwave ovens work the same way, although I have some vague
> recollection that some fancy models have variable power.

I recently purchased a new microwave that has variable output power (labeled
as "inverter technology"). It was sub $100 US so I wouldn't call it
"fancy". It has 4 power ranges and uses duty cycle control between the
power ranges to regulate the 10 available power settings. It is FAR
superior at the lower power settings. When defrosting or cooking on low, my
old microwave would singe and pause repeatedly. Cycling 1/4 power more
often yields MUCH better results.

The new microwave also behaves much better on my small backup generator -
conventional microwaves have really poor power factor AND significant even
order harmonics, both not appreciated by generator voltage regulators. The
even order harmonics are from the voltage doubler magnetron circuit. On one
half of the line waveform, the diode charges the cap up. On the other half
cycle, it fires the magnetron with the cap in series with the line voltage.
Since the back EMF when charging the cap is not equal to the fire voltage of
the magnetron minus the cap charge, the waveform is highly asymmetrical.