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| Microwave oven PWM frequency |
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| SiliconWizard:
--- Quote from: tooki on February 12, 2018, 11:34:00 pm ---Also, there are often two things at work: 1. the duty cycle of the microwave — usually it's 100% at maximum power. At lower power, most microwaves have a PWM frequency in the seconds. Like 10 seconds on, 10 seconds off for 50%. Inverter microwaves (like my Panasonic) seem to both vary the microwave intensity and the duty cycle. --- End quote --- Yeah. Also depends on if it has some kind of "grill" function (usually a quartz lamp or something like that). I have an LG oven that has that. If you use a cooking mode with the Grill function, it will alternate between microwave and grill, making the cycles longer, and you can definitely hear when the magnetron restarts. |
| Red Squirrel:
Why is it that they can't just vary the power level though? It would basically be like a radio transmitter where you can dial down the watts. I imagine most modern microwaves just use a high voltage inverter to power the magnetron now days, so it should be easy to simply dial down the voltage. Or is it more complicated than that? |
| ogden:
Microwave is good only at one job: flash heating. It is awfully bad for cooking or defrost. It means all you need - max power. Well... unless you are victim of toxic marketing and truly believe that you can *actually* cook something with microwave. In such case you are lost anyway and regulation of microwave power is least of your worries :) |
| bob91343:
I just bought a microwave oven and on reduced power it's a few seconds on and a few seconds off. Same with the one I just took apart. That one yielded a nice power transformer to build a hipot tester, which I have done. It's enough of a cost increment to do reduced power cleverly that I understand why they don't do that. We are dealing with a kilowatt or so, not trivial enough to use a little FET to PWM it. Further, there is the filament in the magnetron that needs steady heat, as shown by the fact that the oven doesn't do, say, 12 seconds on and 12 seconds off for 50%, but lengthens the on time to allow for heating filament. |
| soldar:
--- Quote from: John Heath on February 13, 2018, 01:46:06 am --- A microwave oven is switching on and off every 8 m seconds as well as every second or so. The reason for this is it is against the law for a microwave oven to run off a filter DC power supply. It must be a unfiltered supply raw off the full bridge rectifier thus on and off every 8 m second. The reason for this law is to sweep a gigantically stupid law passed before under the rug. The gigantically stupid law was to have a 1000 watt microwave and a tiny 100 m watt WIFI in the same frequency range. The solution , equally as dumb , was to out law filtered power supplies in microwave ovens so that the tiny 100 m watt WIFI can sneak a few bytes out in a 2 m second window between power cycles of a monster 1000 watt microwave. Is it just me or did someone drop the ball here? Thank god for 5 GHz WIFI. --- End quote --- Rather than get into the technical aspects I will ask for a cite that supports "it is against the law for a microwave oven to run off a filter DC power supply." I am quite sure I know the technical explanation of why it is done this way but let's see the law first. Where can I find it? |
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