Quote:
Originally Posted by j.p.s
I haven't seen a microwave oven (in the US) with knobs for decades.
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Available widely in the city, new, today. Well known brands.
Quote:
Originally Posted by j.p.s
The situation for Panasonic microwave ovens with "inverter" technologiy is more complicated than that. (I know nothing about the technical details.) Although there is not a simple power reduction, it is not an on/off duty cycle. On a very low power setting there is brief elevated power draw that is well below full power, then essentially off except for fan, turntable, and lights. But this is not standard duty cycle because water just barely simmering will continue to barely simmer for minutes and minutes. For a conventional duty cycle oven, the boiling would cycle as well. For medium power settings there is a somewhat constant mid level power draw. For a 9 setting the power never is full power. Full power (10) is very close to the rating of my power meter and it continuously beeps loudly in complaint.
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No, the transformer based ones have quite fast duty cycle (giving about 2500V). If the Panasonic is using a magnetron, but inverter instead of an 800W 50Hz/60Hz transformer, then it's storing power in the input capacitors fed with recified AC mains. A Magnetron can't be varied in power. It's a diode with specially shaped anode(s) that inherently pulses at about 10 kHz. It simply doesn't go if you try to reduce the voltage for reduced power. However the huge inductance and filament (fed from HT transformer) means the transformer based ovens can't do the duty cycle at much speed, but an inverter based 2500V supply can cycle on and off faster. Likely they use a separate inverter for the filament which is low voltage and high current.
The lamp / turntable should be unaffected by power setting on transformer based ovens as it's only the transformer that's pulsed. Because the direct cathode filament is usually fed from the same transformer, that also limits cycle speed. You can hear the noise from the transformer laminations as is pulses on and off at lower power.
In the 1940s and 1950s the magnetrons used an electromagnet. Modern ones have Samarium-Cobalt or similar "super" magnets. The transformer has a weld across the laminations to limit current. That has to be cut off if repurposing the transformer for a 500W to 1kW valve (tube) based HF radio transmitter.