Inverter Microwave Ovens

Discussion in 'General Electronics Chat' started by MrAl, Dec 27, 2017.

  1. MrAl

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    Jun 17, 2014
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    Hello there,

    I was looking around and found that several manufacturers are now making inverter mic ovens not just Panasonic anymore. Not sure when this happened, but it's a good thing.

    Drawback is there are still only 10 power levels. If i was going to make one, i'd make it with 100 levels min. THat's so you can get just the right power setting. As some people have pointed out and i noticed too, sometimes the power level you want is in between two power levels you have. It would be nice to have at least 50 levels anyway.

    An inverter can be controlled to put out continuous power at many levels so i think it is not good that they only provide 10 levels on all the ovens i have seen so far.
     
  2. MrAl

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    Jun 17, 2014
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    Hi,

    I meant to ask, anyone else using one of these?
    They are becoming more common now so i expect to see them in wide spread use in the near future.

    One of the things i like most about these is that when you set the power lower, to like power 5 let's say, the input power to the oven actually goes down too it does not pulse from max power to zero power and back to max power again, etc. I made some measurements on a friends oven the other day and measured about 4.7 amps when set to power level 2. The input current and power goes up as the level is increased, up to level 10, which for that oven was close to 15 amps on level 10. I think it was 8 amps for power set level 5 on that one.

    In the summer months it is best that i dont load the line too much so the lower current works out better here. That also means you can run other stuff on the same circuit without blowing the breaker or fuse.
     
  3. Externet

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    Nov 29, 2005
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    Hi Al. No, never used one. Teach me... what does 'inverter' has to do here ? Is it for a yacht/camper/12V ? Or does it rectify mains, pwm a level to the magnetron ?
    Microwave ovens as far as I know work their duty cycle instead of power level. If you want an in-between power setting, could adding a cup of water on the platter manage it ?.
    Would 100 step PWM control hacking do it ?
     
  4. MrAl

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    Hi,

    Well as you know, an inverter (or converter) takes a voltage like 120vac 60Hz and converts it into another voltage like maybe 220vac 50Hz, but can also do a lower voltage at the same frequency like 60 Hz or whatever is needed, and can be made adjustable like 0 to 120vac output at whatever frequency.

    So what they do in these ovens is use an inverter to control the magnetron so as to get a continuously variable power into the device without having to pulse it using very slow PWM. Many ovens use very slow PWM, like 'on' for 10 seconds, 'off' for 10 seconds. Fast PWM would be on for maybe 100us and off for 100us, and that means that he power output of the tube looks continuous, and they probably even filter it into a smooth level.

    So in a normal oven the food would get 1000 watts cooking for 10 seconds, then zero watts cooking for 10 seconds, then 1000watts for 10 seconds again, then zero for another 10 seconds, etc.
    In an inverter oven, the power would be reudce to 500 watts so the food gets 500 watts of cooking power continuously, non stop.

    The effect i see seems to be meat that is more tender, and also as mentioend, the power input to the oven is much reduced too so instead of 1200 watts input going on and off, we see maybe 600 watts continuous, which is lower all the time which is better.

    Until recently i only saw Panasonic ovens like this but now i see a lot of brand names moving to that technology too.
     
  5. Reloadron

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    Jan 15, 2015
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    I was never aware of that feature. That sounds pretty cool. My wife uses all of those sort of features where I just shove something in and go for it. The only cooking power I use is high. :) The current microwave is a 1200 watt flavor and uses the old pulse on and off method. I never measured the power on the mains input, that may be interesting to see.

    Ron
     
  6. Externet

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    Nov 29, 2005
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    Thanks, Al.
    It could be also without rectification and inversion to PWM, just fast AC PWM like one mains cycle on, two mains cycles off, - one mains cycle on, one mains cycle off - two mains cycles on, one mains cycle off - three mains cycles on, one mains cycle off... Would appear as a smoother variable setting...
    Is there large 400V electrolytics inside ?
    Longer 'normal defrost' times also yield tender meats. A factor is the starting point. From frozen or not.
     
  7. MrAl

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    Jun 17, 2014
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    Hi,

    I didnt check the electro's inside there. Maybe next time.
    I never cook meats from frozen because they dont cook evenly.
    I end up using power level 3 for most meats because that seems to get them the most ttender.
     
  8. MrAl

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    Jun 17, 2014
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    Hi,

    Oh yes the power input measurement is quite interesting and is a tell all if you have an inverter because it will be a continuous reading, not changing from high to low then back again, etc.

    The highest level power setting on mine pins the power meter so i cant measure it, but the lower power settings i can measure. I think it was 500 watts or maybe 600 watts on power 3.

    PS. I got my cards out late this year again i hope you got it by now.
     
  9. Reloadron

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    Absolutely we got it and thank you. Hope you had a real nice holiday.
    I need to dig out my little Kill-A-Watt meter and try looking at the microwave.

    Ron
     
  10. Danko

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    Nov 22, 2017
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  11. AnalogKid

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    Danko - GREAT find!

    ak
     
  12. Reloadron

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  13. Danko

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    Nov 22, 2017
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    You are always welcome!:)
     
  14. MrAl

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  15. Danko

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    Nov 22, 2017
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    Seems it is possible with small average microwave energy and very long (20...30 minutes) cooking time.
    Problem is we can not maintain temperature of water, encapsulated and thermally isolated in egg's medium, close but lower its boiling point.
    Edit: Sorry, if it is about 15W, 4.5kOhm resistor - then it may be. :)
     
    Last edited: Dec 29, 2017
  16. MrAl

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    Jun 17, 2014
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    Hi,

    Yes it was kind of a joke about that really big power resistor.
    I have some big ones too and long time ago some 300 watt power resistors, but that comment was just joking. They do get hot too, very hot, so i know they can easily boil water as i have done that with them too. Using water as a heat sink, you can see bubbles start to form after awhile.
     
  17. Danko

    Active Member

    Nov 22, 2017
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    Yes, power resistors are often used as heating elements:
    http://www.digikey.fi/Web Export/Supplier Content/Riedon_696/PDF/riedon-an-resistors-as-heaters.pdf
     
  18. strantor

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    Oct 3, 2010
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    I think the switch to inverter microwaves is a sad development. Where are we supposed to get extra-cheap high VA mains transformers in the coming decades? I wish failure on the microwaves of all whom I know, so that I can harvest their precious MOTs. These inverter microwaves have no value to me.
     
  19. debe

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    Sep 21, 2010
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    Don't worry Strantor, there will still be plenty of old style microwave ovens around as they are cheep. Ive seen a few Panasonic inverter ovens in the scrap yard as the customers considered them too expensive to fix the inverter when it fails.
     
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  20. Reloadron

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    That thought crossed my mind also. There was a time when there was good junk to be had but now most of it is just junk.

    Ron
     
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