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Reduce power of a microwave oven?

Discussion in 'Electronic Repair' started by mike, Jan 18, 2011.

  1. mike

    mike Guest

    My 27 year old microwave oven was down below 400W output and taking a long
    time to heat my coffee.
    So, I went out and bought a 1100W one.
    Big mistake.
    It works fine on coffee, but WAY overcooks small stuff.
    Yes, it has a power level setting, but the on-time is 15 seconds
    and they modulate the off-time.
    I tried to heat a frozen hamburger patty. It boils the liquid around
    the outside for 15 seconds, but the inside is still frozen.
    This really messes up the cheese stuck to it. If I leave it in
    the frozen burger, it comes out awful.

    What are my options for reducing power?
    Yes, I can stick in a pot of water to absorb energy, but I'm
    looking for a more elegant solution.
    I assume there's nothing I can do on the primary side, cause of the
    filament voltage requirements.
    Assuming I can find a switch that can take the voltage and current,
    can I switch the value of the big cap? Not much else in there to play with.

    Alternatively, there's stuff they put in the bottom of microwave popcorn
    that heats up from microwaves. What is that stuff? Maybe I can find a
    pan with that in the bottom to average out the energy over time.
    There's a "as seen on TV" serving plate that you heat in the microwave.
    It's made of granite. What is it in the granite that gets heated?
    IF I could find a square of floor tile in ceramic or granite, ceramic is
    more easily available, I could stick one of them in the bottom of the oven.

    Thanks, mike
  2. Can you return the oven? You can use the argument that it's not fit for its
    intended purpose. Which it isn't.

    I always assumed variable power was simple duty-cycle variation --
    pulse-width-modulation -- over a fraction of a second. That the "on" time
    would be fixed at 15 seconds (!!!), with the off time varied, is absurd. It
    would produce exactly the effect you see.

    There's also the possibility your sample is defective.

    The stuff at the bottom of a microwave-popcorn bag is called a susceptor
    sheet. I think it's a ferrite material, but I'm not sure.

    Without any food to absorb heat from the susceptor, it would probably
    overheat and burn fairly quickly.

    You might try putting a brick on the oven, on the remote chance
    fire-hardened clay absorbs microwaves. Bricks made with metallic colorants
    might be the best place to start.
  3. mike

    mike Guest

    RTFM reply when I stated EXACTLY how the power setting works.
    How about RTFOP?
  4. mike

    mike Guest

    Nope, my inability to forecast the consequences is not the fault of the
    Yep, that's the way most of 'em work. The problem is the filament in
    the magnetron. Much shorter and you don't get any power out cause
    the filament ain't hot yet. With enough mass inside the oven, it
    averages out pretty well. For a single frozen hamburger at 1100W, not
    so much.

    Yes, you can buy a microwave with fine-grained setting of continuous
    power at most any retailer...for 3X the price.
    They have to keep the filament hot while reducing the power. Much more
    complicated and not a commodity item >> much higher price.
    They used to make browning plates with some kind of susceptor in the bottom.
    Seems the only place you get 'em today is from TV infomercials at
    high prices or on ebay at antique prices.

    I do have a microwavable trivet that claims to be made from granite.
    Gets hot alright, but it's encased in plastic and not well coupled
    to whatever you put on it. A couple of experiments suggest that
    while it does divert significant power, it will probably overheat
    trying to do what I want.

    A cup of water solves the problem, but it's not very elegant.
    There's considerable range of microwave absorbency. I was hoping to find
    some kind of commonly available ceramic, like floor tile, that
    would work. That's why I asked for input.
    Wonder what Home Depot would think if I packed tile samples
    into the employee lounge and stuffed 'em into the microwave?
  5. Mr. Terrell apparently shoots from the hip and never apologizes.

    Comment on quaint Usenet customs, from Usenet:

    To me, the *plonk...* reminds me of the old man at the public hearing
    who stands to make his point, then removes his hearing aid as a sign
    that he is not going to hear any rebuttals.
  6. Mike-

    Does the new microwave have a Defrost option? If so, does it also cook
    for 15 seconds at full power?

    I had a small microwave back in the 70s that had a low power setting.
    My memory is a little hazy, but I think the low power setting switched a
    capacitor in series with the high voltage transformer primary. It acted
    as a ballast to reduce magnetron voltage.

  7. PeterD

    PeterD Guest

    Or use the defrost cycle!
  8. Can you return the oven? You can use the argument
    If your description is correct, the oven is grossly misdesigned. You do not
    implement variable power by turning the magenetron on for 15 seconds, then
    letting it sit for a minute! I've /never/ seen a microwave oven that works
    that way. My home GE works fine, as do all those I've seen where I've

    I've never heard of varying a magnetron's power by adjusting its filament
    voltage! I've always ASS+U+MEd there was some way of turning the tube on and
    off by varying an electrode voltage. (Simply pulsing the anode voltage would
    produce variable output.)
  9. Bacon, eggs, burger were some examples.

    A microwave oven is ideal for bacon, because all it needs is a thorough
    heating. Which is all a microwave oven does... It doesn't actully /cook/
  10. Lab1

    Lab1 Guest

    Many new microwaves have and auto-defrost function (also usually an
    auto-reheat) that measures the humidity while firing the magnetron for
    short bursts. It runs this cyclically for a preset time based on your
    food selection and weight while it calculates the actual time it should
    take to defrost the food. Then it usually beeps once and finally runs
    the defrost cycle that it calculated.

    I find this works quite well once you get the hang of it.
  11. All of the bog-standard microwave ovens that I've owned have worked
    Fascinating. (In the correct Spock sense... "Fascinating I reserve for the

    I have a high-power GE microwave oven cum exhaust hood. Many foods -- such
    as soup or oatmeal -- must be heated at half power (give or take), or you
    get localized boiling, sometimes very quickly. I've never seen this happen
    with reduced power. The oven always acts as if the magnetron is being
    rapidly pulsed.

    May I publicly apologize for believing that manufacturers ever use the least
    bit of common sense when designing products?
  12. Your perfectly logical definition seems sufficiently generic to include
    microwave ovens. In practice, "cooking" refers to either immersing
    the-thing-to-be-prepared in a cavity full of hot air...

    "Yeah, Sommerwerck -- yer mouth."

    ....(baking, roasting) or applying heat directly to it (frying) or from a
    nearby source (broiling, grilling). Microwave "cooking" does none of
    these -- it simply heats the-thing-to-be-prepared from the inside.

    Oddly, the Wikipedia article claims that microwave cooking heats food more
    evenly than any other method, when, in fact, it heats from the outside in,
    as does every other cooking method, and can be extremely uneven, if part of
    the dish is sitting in a standing-wave node.
  13. PeterD

    PeterD Guest

    let's face it, most cooking is just heating.
  14. PeterD

    PeterD Guest

    Huh? Virtually all the ones I've seen do just that: run a 10 to 15
    second on/off time cycle. The magnetron is turned on with a relay, so
    rapid cycling just begs to blow that relay.
  15. If your description is correct, the oven is grossly misdesigned.
    I could easily test this with frozen bagels. Do you want me to? I'm not much
    in the mood.
  16. Jeff Layman

    Jeff Layman Guest

    My Panasonic has an inverter. Works OK, and and an energy meter
    confirmed that it doesn't just cycle from full power to off when running
    at lower power levels.

    But it does tempt you to experiment. Even though the guidebook warns
    against trying to "boil" a perfectly cooked egg in its shell, I thought
    it worth trying using lower power levels. The first egg was perfect,
    using a rather complicated cooking schedule. The second was very soft -
    barely cooked. The third I'd rather forget, but it took a long time to
    clean the oven, and SWMBO wasn't amused as she was standing almost next
    to the door when it was blown open. It also took me some time to repair
    the safety lock...
  17. .... which should give further pause to those who claim that Wikipedia is
    full of good, accurate information ...

    Comment on quaint Usenet customs, from Usenet:

    To me, the *plonk...* reminds me of the old man at the public hearing
    who stands to make his point, then removes his hearing aid as a sign
    that he is not going to hear any rebuttals.
  18. mike

    mike Guest

    You're just DETERMINED NOT TO READ the original posting...where I
    mentioned that too.
    Although, I'd not considered adsorption as a relevant process.
  19. It is. No one is claiming it's always absolutely perfect.
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