Monday, June 25, 2012

Measuring the voltage and current of a microwave oven magnetron

I took apart my microwave oven and measured the voltage and current supplied to the magnetron. The device appears to start conducting current at 4KV, and will allow lots of current to flow once this threshold voltage is reached.

My current probe is pretty cheapo, so I wouldn't trust its measurement too much, but the final determination of 1300 W average seems pretty spot-on.

1 comment:

  1. Hi Ben - this video was from quite a long time ago, but it looks like you are still active here, so I'm hoping I might get in touch to discuss your magnetron measurement. I was doing some research on this recently, and I think you might be the only person who has taken this direct measurement and shared the results publicly. I do not have the gear to measure this high voltage circuit directly (though I'm tempted to get some). Anyway, when I work it out theoretically, I think I would expect to see a DC-offset sine wave at the magnetron cathode. The capacitor provides the negative 2,000 VDC as you say, so I believe we should see a sine wave and not a square wave as your scope shows. I'm puzzled by this and wonder if you have any thoughts. The reason for the current lag actually could be that it is real - if we assume a threshold voltage around 3,200 V for the magnetron to activate (from manufacturer spec sheets), then it would go active part way down the negative swing of the sine wave, likely coincident with where your current probe is shown current starting to flow. This still doesn't explain the square wave though. On a different topic, have you ever taken similar measurements on an inverter-powered microwave? I'd be interested to hear responses to any of the above - I can be reached at trevor (at) trenic (dot) ca. Cheers!