Talk:Microwave oven/Archive 1

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Efficiency

Is there any data on the efficiency of firstly a magnetron and secondly the efficiency of food heating? —Preceding unsigned comment added by 151.182.136.76 (talk • contribs) 14:11, 28 August 2003

http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_009 says (without explanation) that magnetron efficiency is about 75% and oven efficiency is 50% to 60%. This ignores other factors, such as the ability to boil a single cup of water without having to heat a whole pan. -- Heron 07:50, August 28, 2003 UTC

I want some information purely on energy efficiencies of cooking a kg of potatoes in a gas (which most do), in eletrical heater, in oven and in a Microwave Oven. In terms of calories first. And then in terms of cost of fuel in a chosen market. (not cost of time taken, cost of oven etc) For example x calories of gas will cost less than x calories of electrical energy. And far less in Iran than in UK. What is smarter and how much smarter. —The preceding unsigned comment was added by 59.93.240.251 (talk • contribs) 22:34, March 20, 2006 (UTC)

The efficiency paragraph currently posted (Aug 17 2006 early AM) is quite accurate. For one thing, compare the manufacturer's hype ("700 watts of cooking power!") with the nameplate power consumption (usually well over 1000 watts). Another thing is look at a magnetron and notice the massive cooling fins through which a large cooling fan blows. Since the cooling fan sucks all the air from around the electronics (ie. transformer heat) and blows it through the magnetron then out into the cavity where the food is, an unscrupulous manufacturer could almost claim the nameplate wattage as the cooking power. But they don't. The efficiency could vary somewhat between models and loads (ie the food inside) but I would bet it would be substantially accurate if one were to perform an input power versus delta-t of water experiment. Remember a magnetron is a triode, has a forward voltage drop, and basically works by creating turbulent swirls of electrons... and electrons have mass. And BTW if a gas stove turns out to provide better BTUs per buck, that is the smarter heating appliance for that application, even though I believe the microwave oven is probably the most efficient in terms of line-cord-power-in to heated-stuff-on-a-plate-output. Remember, you're more interested in what the cost per BTU of heat you successfully apply to your load than you are with the unit cost of a given fuel. -- Electrical engineer, fmr. Litton (Decca Radar) employee, have restored my own Amana Radarange. —The preceding unsigned comment was added by 216.138.194.68 (talk • contribs) 21:40, August 16, 2006 (UTC)

POV?

The second half of point 2 and point 4 of the hazard list sound like attempts to scare people. See for example the phrase: "Microwaved food contains both molecules and energies not present in food cooked in the way humans have been cooking food since the discovery of fire...". That is not a scientific argument to assess the safety of microwaved food. The point about energies is utter nonsense. The point of the molecules sounds dramatic, but in fact, every new vegetable contains hundreds of chemical compounds that are not present elsewhere. And this phrase: All foods that were processed through the microwave ovens caused changes in the blood of the volunteers.. It is not claimed that the changes were larger or more dangerous than after consumption of other foods.

What happened to Hertel is not nice, but "freedom of expression" is an issue different from "scientifically correct".

I will remove section 4. If you want to revert it, present it as NPOV with counter arguments. —Preceding unsigned comment added by Hankwang (talk • contribs) 10:51, 17 March 2004

I have removed most of the scare talk and replaced it with (I believe) a short NPOV paragraph. -- Hankwang 12:25, 17 Mar 2004 (UTC)

Wireless frequency

The frequency range used by microwave ovens is same as that used by wireless devices operating in the ISM band. Why doesn't everyone get 'cooked'? -- Bharath 14:56, 8 April 2004 (UTC)

A microwave oven pumps out several hundred watts of power, but the regulations for the ISM band limit the transmitter power to about 100 milliwatts per device, which is several thousand times less, and not all of that power is absorbed by the human body. Standing close to an ISM transmission does indeed heat you up, but only by a small fraction of one degree, and certainly not enough to cook you. -- Heron 11:03, 9 Apr 2004 (UTC)

There is another reason that ISM phones don't cook, while microwaves do. Microwaves set up standing waves inside the metal cabinet, which amplify each other and can far exceed the power of the microwave. (a 1kw microwave could easily set up a 10kw standing wave- it would only take 10 cycles, which would happen in the blink of an eye). An ISM phone radiates, and no standing waves are set up in you head. So they are generally safe. —Preceding unsigned comment added by 168.215.143.134 (talk • contribs) 13:46, 31 May 2005

Standing waves do not amplify each other. If a microwave has a power output of 1kw, it cannot create a 10kw standing wave. This would violate common sense and conservation of energy. The metal cabinet contains the waves so that they are concentrated on the food, whereas a phone radiates most of them away. Pfalstad 21:47, 7 October 2005 (UTC)

Yes and no. Average power can't be increased, but a cavity can "store waves" which transforms impedance and greatly increases the e-field, same as any tank circuit does. Another way to visualize this is as two high wattage waves propagating in opposite directions, but summing to a much smaller average energy flow in a single direction. Inside a cavity, a partially transparent object or very reflective object (weak absorbers with mismatched impedance) can act as strong absorbers because they are part of the "resonant circuit." Though I think these impedance-match effects wouldn't apply that much to human heads with cellphones, since human heads are good absorbers. Also, power density in a cavity resonator does not decrease as 1/r^2 as it would with a bare antenna... so inside a microwave oven the radiation tends to hit the food, while with a cellphone much of it misses your head entirely. --Wjbeaty 06:48, 19 January 2006 (UTC)

"Doesn't cook" doesn't mean "no damage". This treatment needs some depth. There have been persistent reports of increased cataract frequency and cardiovascular problems (loss of tissue elasticity) associated with microwave exposure; e.g., from leaky microwave ovens. Industry pressures may have distorted research result reporting here. Second, there is genetic damage. The US Embassy in Moscow was bombarded with microwaves during the Cold War to power the many embedded listening devices. Although metal "sun screens" were installed on the windows and medical exams were conducted on personnel, an association of State Dept office secretaries doubted official pronouncements and sued for release of the medical data. I think some had non-government doctors repeat some tests. The upshot was an elevated incidence of damaged chromosomes (this was before the revolution in genomics and cellular biology). Government security considerations definitely distorted the reporting of research results here. OK, prod me to do the research -- I have to get the morning coffee & chores done and only visited here because the kitchen magnetron blew out y'day from old age. jerry-VA@prodigy.net —Preceding unsigned comment added by 69.17.65.119 (talk • contribs) 12:14, 25 October 2005

Arching?

Does anyone know sufficient enough information on arching? I really want to learn more about it, but there doesn't seem to be too many resources on it. Anybody want to make a page in wikipedia? ;) —Preceding unsigned comment added by Macaddct1984 (talk • contribs) 03:46, 19 February 2005

How about corona discharge, electric arc, electrostatic discharge, electrical breakdown--Wjbeaty 18:20, Mar 4, 2005 (UTC)

I think you mean "arcing". See "Electric Arc". roger knutson —Preceding unsigned comment added by 24.118.8.60 (talk • contribs) 23:08, 2 October 2005

Marvin Bock

This article credits Percy Spencer with the invention of microwave cooking, although I have heard accounts that a technician called Marvin Bock who worked for him should be given more credit for this. It seems unlikely that it would take 5 years between the invention of the cavity magnetron (in 1940), and its subsequent widespread production and use in WWII, and the discovery of its effect on matter containing water in 1945/46..... —Preceding unsigned comment added by Zootalures (talk • contribs) 17:30, 13 March 2005

My dear father, Marvin J. Bock (1914-1971) was an electrical engineer in Percy Spencer's R&D laboratory at Raytheon, and did indeed participate in the development of the microwave oven during the 1940s. In September 1984, Dr. John M. Osepchuk published "A History of Microwave Heating Applications" in the IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-32, No. 9. Page 1205 of that publication states, in para. 2: "Enthused Raytheon management sponsored a contest for a name for the microwave oven and the Radarange (TM) was born. Marvin Bock, who later worked with Tom Philips, today's CEO, built the first radarange, the Model 1132, which provided an output power of 1.6 kW from one water-cooled, permanent-magnet magnetron. This is shown in Fig. 3. Note that it was a free standing white-enameled unit operating from 220 V." Mr. Bock held five U.S. patents, including one related to microwave heating: #2,516,503 issued in 1950 and titled "Controlling Device for Cooking Apparatus". It discloses a means for shutting off microwave power when a food load is not present in a microwave cooking system. -- Peter A. Bock (1942- ) —Preceding unsigned comment added by 24.20.85.170 (talk • contribs) 07:11, 26 March 2005

Metal

Some note should be made under the safety list about the potential danger of microwaving metal. Nerd65536 23:50, 14 July 2005 (UTC)

Proposed merger

Since this is tagged, but with no discussion, I'll start it. Gene Nygaard 14:20, 29 October 2005 (UTC)

Merge under "Microwave oven" title. Both deal with cooking (other uses can go under microwave), more logical place to put it, more likely to be looked for and linked from than "microwaving". Gene Nygaard 14:20, 29 October 2005 (UTC)

Merge under "Microwave oven". Pfalstad 22:23, 31 October 2005 (UTC)

empty links?

The links to Microwaving directs back to here...So I went a head and removed them...--64.114.83.91 02:19, 12 November 2005 (UTC)

Carcenogenic containers

There isn't any information here about the notion of whether microwaving foods in certain containers can cause carcinogens to the leech from the plastic into the foods. Whether or not this is supported by any evidence I don't know, but it's certainly a source of worry to some people, and so should probably be mentioned. — Asbestos | Talk (RFC) 16:36, 13 December 2005 (UTC)

explosion of distilled water

I was watching an episode of myth busters on discovery channel and they address the issue of distilled water exploding as a result of super heating and they mention that distilled water would explode if you put a spoon in it or add other molecules and I think that the part of the article that notes the super heated explosion of distilled water as a myth should be changed —Preceding unsigned comment added by 198.45.19.20 (talk • contribs) 17:42, 12 January 2006

The myth is that only destilled water can be superheated - all water can be superheated. The article is correct. Mossig 18:14, 12 January 2006 (UTC)

Right, the "distilled" requirement is a myth. Don't forget that the main problem with superheating involves explosions of very impure water: coffee or instant soup. It's not distilled water that causes explosions, explosions result from overheating of bubble-free water. Water which lacks any microbubbles as "nucleation centers" will not boil unless raised several tens of degrees C above 100C. Vacuum packed liquids such as canned soup or tomato sauce will lack microbubbles, and will tend to explode rather than boil normally. So will coffee or tap water if it has been de-gassed by being boiled and cooled previously. --Wjbeaty 06:56, 19 January 2006 (UTC)

15 minutes' continuous use

When a domestic microwave oven is used for more than about 15 minutes the performance is said to drop slightly. Does it mean that after using the microwave for long time continously that food needs microwaving longer to ensure it's cooked properly? Can we expand on this and mention it within the main article? —The preceding unsigned comment was added by 82.31.18.211 (talk • contribs) 13:51, 11 February 2006 (UTC)

There is no noticable drop in output from a good quality machine. If the output does decrease with time, it is not enough to affect cooking performance. --Blainster 22:05, 11 February 2006 (UTC)

Why does this happen? Is this problem only apparent in domestic and not commercial microwave ovens? —The preceding unsigned comment was added by 82.18.192.12 (talk • contribs) 17:05, 12 February 2006 (UTC)

It does appear to be a real effect, as it's mentioned in this Which? report on domestic ovens. My guess is that, since a magnetron's frequency is temperature-dependent [1], it moves away from the resonant frequency of the cavity (the oven chamber) as it warms up, so it transfers less energy to the chamber. If this is the reason then it will apply to commercial ovens too. --Heron 13:27, 15 February 2006 (UTC)

The cavity is typically not resonant for the microwave frequency. Rather the effect may be due to that modern microwave oven magnetrons are equipped with a thermal protection switch, which shuts off the magnetron when its temperature gets to high. The rest of the microwave is still operating, in order to get a god airflow arond the magnetron to cool it down. When its cold i automatically starts again. The user will typically not notice the on-off-on cycle of the magnetron other than that the mean power of the microwaves gets lower, and the cooking times correpsondingly longer. (Maybe one should do some experiments.... It should be easy to decide which of the effects that is reposnible for the longer cooking times.) Mossig 17:43, 7 May 2006 (UTC)

Can we mention this in the article then? —The preceding unsigned comment was added by 2006 82.18.198.109 (talk • contribs) 10:40, 18 February (UTC)

If it is not from a published source, it cannot be used in Wikipedia. Unreferenced personal knowledge is considered a form of original research, and thus not allowed. --Blainster 02:07, 10 May 2006 (UTC)

I removed the mention of 15 minutes from the article, since the source was not found.62.142.46.22 13:13, 20 August 2006 (UTC)

Power control

The microwave oven I have has different power settings: maximum 900W, then 600W, 450W and so on. But after buying it I discovered that actually these different "power settings" just meant turning the magnetron on and off periodically, over a 30 seconds cycle. For instance, "600W" means turning it on 20s and then off 10s, giving a 600W average.

I strongly suspect this is the case for all microwave ovens. Can someone confirm? Is it that the power of a magnetron is set by construction, and cannot be controlled?

This issue has its importance for short cooking times. I feel these facts should be known. In particular, it a bit misleading for microwave vendors to label the different power settings as if they implied different continuous powers. -- David Olivier olivierd 01:09, 16 February 2006 (UTC)

Yes I believe it is true of all microwaves currently on the market to-day, although if memory serves there was a shutter of sorts on some early designs. The reason is that magnetrons cannot be 'dimmed' as it were like a light bulb - they can only operate at their specified power. --DV8 2XL 01:42, 16 February 2006 (UTC)

Panasonic claims their "Inverter" technology offers constant power at low and medium settings - instead of simply switching the microwave on and off, read more about it here:

http://www.panasonic.co.uk/technology/inverter-explained.html

and then draw your own conclusions. 82.18.193.47 00:00, 17 February 2006 (UTC)

There you go - make a statement, and some company will make a fool out of you! --DV8 2XL 18:17, 18 February 2006 (UTC)

I was hoping there'd be a section to explain how the inverter microwaves worked. I knew they existed, but was curious about the mechanics. Is Panasonic the only brand that can boast this feature? If we can find good info on this, I think we should add it to the appropriate section. Ckamaeleon ((T)) 17:05, 5 June 2006 (UTC)

I'd guess that 1) the Panasonic ovens don't use a 60 Hz transformer but instead use a high-frequency switched-mode power supply. This is certainly lighter and, nowadays, may well be cheaper than a line-frequency transformer. Then, 2) they realized that they could rapidly pulse width modulate the SMPS, producing what the user perceives as true variable power (as compared to the usual "On for five seconds, off for five seconds" very slow pulse width modulation). Atlant 18:01, 5 June 2006 (UTC)

Acute Dangers

The acute dangers part of the article is clearly B.S.. I am not truying to be rude, but the dangers are greatly exaggerated, and the overall tone of that section is hilarious, funny, and not encyclopedic. Could this be rewritten? --67.49.215.174 02:22, 20 February 2006 (UTC)

Yes it could. Just click the "edit" link. --Heron 19:23, 28 February 2006 (UTC)

Metal shelf

Why do some microwave ovens allow to use metal shelfs to be put in them? With their long metallic structures they seem quite comparable to forks. Still, it is safe to use them. --Abdull 10:37, 7 April 2006 (UTC)

You don't see sharp tines on the metal shelves in a microwave. It isn't the "long metallic structures" you have to worry about, it is sharp edges. From the article itself:

the pointed ends of the fork will act to concentrate the electric field formed at the tips. This has the effect of exceeding the dielectric breakdown gradient of air, about 3 megavolts per meter (3×106V/m), causing sparks to form.

- Bloodshedder 17:11, 7 April 2006 (UTC)