Comments on Why does AC frequency affect my microwave's RPM?
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Why does AC frequency affect my microwave's RPM?
I used to live in the United States, and my microwave ovens' turntables turned at six rotations per minute (RPM). I now live in Israel, and my microwave oven's turntable rotates at five RPM. Annoyed at this[1], I mentioned it to someone, and he intimated that this is due to the AC frequency (60 hertz in the States but 50 here). Can someone please explain what the AC frequency has to do with the turntable frequency? What exactly is AC frequency[2], and how does it affect the turntable frequency? I've checked out the Wikipedia articles on utility frequency and alternating current, but they don't explain this point.
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Why was I annoyed, you ask? Because my microwave oven has a thirty-second button, but the food winds up at the back. ↩︎
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It's entirely possible that if I really understood what AC was, I'd also understand what AC frequency is. I don't really know what it means to be changing the direction of the electricity flow every hundreth or 120th of a second. ↩︎
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The turntable is apparently run by a cheap synchronous motor. There is a type of motor that's easy to manufacture, that turns synchronously with the line frequency.
You say the table used to rotate at 6 RPM with 60 Hz power, and now rotates at 5 RPM with 50 Hz power. That is exactly what you'd expect from a synchronous motor.
The turning of the food in a microwave oven is only to even out the effect of hot and cold spots. It's not very critical, and whether one turn takes 10 seconds (6 RPM) or 12 seconds (5 RPM) doesn't matter.
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