Slow microwave ovens

[FMurtz]

Do it all the time, for ten seconds for one or two eggs to bring to room temp from the fridge.

[Bill Wright]

They are used judiciously.

Bill

[Arthur Conan Doyle]

Found a site that said GE and Whirlpool used to license the patent, but no longer do. Just did a quick Google patent search - there are more than one related to the use of an inverter to control the magnetron, all held by different companies.

IIRC patents are only good for 17 years or so. Seems like they would have expired by now.

[FMurtz]

Pest, making me use google.

[Bill Wright]

I don't find much use for the 1,200W setting. The only real use is for heating water quickly when the kettle's broken. Even jacket spuds are cooked unevenly. Thick soup needs to be stirred during cooking. Meat is hopeless.

Bill

[Bill Wright]

Rewire to use 2kW? Do you live in a tent?

Bill

[Bill Wright]

I have two. They do. They don't cycle.

Bill

[mike]

They adjust the AVERAGE power at a rate much faster than the thermal time constant of the food.

I don't think you can change the operating voltage far enough to get a large enough range of power. And how would you do that anyway? You'd have to use an inverter to do it efficiently. Might as well just switch the power on and off directly. Everything works at optimum efficiency or is off.

Break an egg into a bowl. Stick it in the microwave on high. Be ready with the cleaning supplies to get the egg off the inside of your oven. The yoke usually explodes first. If you break the yoke, the whites will explode anyway. You really have to whip it up to prevent explosion.

You can get a similar effect with soup.

Might have been a design tradeoff to let the magnetron run too hot and need 15 seconds for it to cool down sufficiently.

I don't remember any explosion issues with my old 600W Amana. My Panasonic Inverter on High will explode an egg faster than you can say, "oh crap, I forgot to cover the dish."

[Johnny B Good]

I knew the inverter types could still only rely upon variable duty cycle heating control like the earlier voltage doubling HT transformer/ rectifier/HV capacitor designs did. I just wasn't quite sure what the benefit of an inverter over a simple voltage doubling circuit was until you let on about the cathode heater/filament being able to remain fully powered throughout the whole cycling period.

This 'cathode filament/heater always on' aspect isn't the only benefit of an inverter type allowing a higher cycling frequency to be employed, it also provides a well regulated HT voltage, free of the 50/60 Hz ripple which spoils the efficiency of the magnetron in the older designs.

The HT voltage (and anode current - no longer affected by heating/ cooling cycles imposed upon the cathode) has to be kept to within a fairly tight tolerance (by the standards typical of domestic white goods) for optimum operation at the correct microwave frequencies.

The effect of changing anode voltage is analogous to the effect of how hard you blow across the open top of a beer bottle (empty or partially empty) to generate a musical tone. The stronger you blow, the higher the sudden jump in pitch will be. The microwave frequency produced by a magnetron is likewise affected by how strong a voltage is applied to its anode and will jump in frequency just like a blown beer bottle and for exactly the same analogous reason (electrons rather than air molecules being involved in this case).

In short, the only way to control the power output of a magnetron without detuning it from its optimum 'microwaving' frequency is by using variable duty on/off cycling. There's no smooth continuous analogue power control option in this case.

As for those large 2 and 3 KW microwave ovens used in commercial kitchens, they use a much larger cooking cavity so that a bunch of "Five Minute Meals" can be heated concurrently in the recommended 5 minutes rather than be processed in batches of just one or two at a time.

The microwave energy doesn't magically focus in the deep interior of the food and heat it from the inside outwards. The microwaves only penetrate the first centimetre or two before losing sufficient of their energy in this process so as to have insignificant effect on the deeper interior which therefore relies upon conduction from the hotter outer portions to raise its temperature sufficiently to kill any pathogenic micro-organisms so as to eliminate the risk of food poisoning.

This, as has already been pointed out, takes time and, surprise surprise, doubling the rate at which microwave energy is being poured into the outer layers of the foodstuff in question, does not halve the time required to complete the cooking process.

Indeed, as has also been pointed out, such an increased rate of energy input will tend to overheat the outer layers so much so as to overcook them. The increased temperature will simply result in a higher rate of radiative and convective heat loss back into the cooking cavity with rather less than you may have imagined making any useful contribution to raising the deep interior temperature of the foodstuff in question.

HTH & HAND! :-)

[Brian Gaff]

I had a Phillips like that, it made no difference but the problem is one of standing waves inside the cooking cavity, and hot and cold spots due to those. Brian

[Andy Bennet]

LOL. I have a 14.4kW electric boiler. That's what I call spin.

[Andy Bennet]

That's why microwave ovens operate at 2.4GHz - the resonant frequency/maximum absorption of energy in water molecules.

[Max Demian]

I don't know what the low settings are for. All the instructions I've seen - e.g. on ready meals - say "full power". There is the defrost setting, but microwaves aren't very good at defrosting as they don't heat frozen water very well.

[Harry Bloomfield]

I have not seen a rotating waveguide in a domestic micro for years. The rotating plate in the base seems the better solution and less complex.

[Harry Bloomfield]

Bill Wright has brought this to us :

I never cook meat in the micro, it is horrible. I do sometimes reheat it. With all things apart from liquid, or with a high liquid content, I stop and stir often. Spuds I rotate, to try to even out the cooking.

[Harry Bloomfield]

Max Demian has brought this to us :

Mine defrosts just fine. You select the weight of the food, then press go. Ice doesn't melt so easily, but once the outer begins to defrost, penetration and absorbsion works just fine.

[Mr Pounder Esquire]

[William Gothberg]

That's not really much more is it? Not even twice as fast.

[William Gothberg]

Domestic ones already have power level control. Simply use that if you cook weird stuff.

[William Gothberg]

Stop giving bad advice.