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Author Topic: Why Does A Microwave Oven Lose Power Whilst In Use ?  (Read 5841 times)

neilep

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Dearest Microwave Ovenologists ,

As A Sheepy I of course know all that there needs to be known about microwave ovens...open the door..whack it in ..push a button and voila !!...a defrosted loaf of bread is ready for toasting.



Take a look at Mrs Arbuthnot of 22, The High Street, Chesham.



Mrs Arbuthnot of 22, The High Street, Chesham earlier today.



She's a fine plucky filly of a girl who knows how to prepare a hearty meal for her husband....and she does it all with a vacant smile too.

Later, she'll have his slippers ready and offer her husband a drink when he arrives home from work.  After dinner she'll end the day by giving him a good old rogering in the bed chamber...all the while, she'll be compliant, grateful and still display her vacant smile.  Well done Mrs Arbuthinot...ewe know your place !!

But hark !!...Mrs Abuthnot does not realise that when she cooks her meal in the microwave that the microwave itself will diminish in power the longer it is used. I am not talking about a period of years but literally after a few minutes or so.

I know this because I read a magazine that reviewed microwave ovens ( I think it was called Microwave Oven Monthly or something)....in any case...it was pointed out how the microwave ovens reduced their power output during the tests !

Why is this...?..why do microwave ovens lose power over a short period of cooking time ? Why is it so difficult for them to maintain a regular power output ?


If ewe can explain it to me then I can try and dumb it down for Mrs Arbuthnot.


Thanking you


hugs & Shmishes


mwah mwah mwah




neil
Do Small People Micro-Wave ?...*le groan*
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« Last Edit: 06/02/2010 00:31:59 by neilep »

Geezer

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Why Does A Microwave Oven Lose Power Whilst In Use ?
« Reply #1 on: 06/02/2010 02:22:24 »
Blimey! I did not know that. I just recently received my copy of Microwavers Digest (I assume is the periodical to which you refer) but I have not studied it yet. I keep my copy in the downstairs bog (Mrs G prefers that I frequent the upstairs bog as infrequently as possible.)

But, as usual, I seem to have strayed from the topic. Where were we again? Oh, yes - power "fluctuations". I would hazard a guess that something in the circuitry that produces the microwaves gets a bit toasty, so they have to limit the power to prevent things from getting too toasty. It may be the actual microwave generating thingy itself (magnetron, jumbotron, mumbletron, or whatever they call it) which is probably the most expensive part of the oven.

So, they can use an el cheapo magnetron with a 600 watt output or a more expensive magnetron with a 600 watt output. The consumer thinks they are getting a 600 watt microwave, and they are, but the cheaper version can only generate 600 watts for short intervals, which means it takes a lot more time to actually heat the stuff in the oven.

I suppose microwave ovens should be rated in "continuous watts" rather than "watts". Continuous watts would tell you the real heating capability.

It's a bit like old fashioned photography flash bulbs. Those little bulbs must have put out as much light as you would get from a couple of kilowatts of filament light bulbs. So, you could say they were 2 kW bulbs. But they could only produce that output for a fraction of a second.

RD

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Why Does A Microwave Oven Lose Power Whilst In Use ?
« Reply #2 on: 06/02/2010 03:51:35 »
Heat damage to the cathode ? ...

Quote
Magnetron - the microwave producing tube includes a heated filament cathode, multiple resonant cavities with a pair of permanent ceramic ring magnets to force the electron beams into helical orbits, and output antenna...

The filament and cathode are one in the same and made of solid tungsten wire, about .020" (.5 mm) diameter, formed in a helix with about 8 to 12 turns, 5/32" (4 mm) diameter and just over 3/8" (9.5 mm) in length.
The cathode is coated with a material which is good for electron emission...

Low output. Occurs as cathode emission decreases from long use. Symptoms: Reduced cooking power.
http://www.repairfaq.org/sam/micfaq.htm#mictstmag
« Last Edit: 06/02/2010 03:53:33 by RD »

Geezer

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Why Does A Microwave Oven Lose Power Whilst In Use ?
« Reply #3 on: 06/02/2010 03:57:31 »
Ah! I did not know that either RD.  ;D

So, if you want to maintain the power output of your microwave, it's best not to use it!

I wonder if anyone sells a calibration device? How much do you think people would be willing to fork over for a calibrated polystyrene cup, a bottle of water, and an old stopwatch?
« Last Edit: 06/02/2010 04:08:56 by Geezer »

syhprum

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« Reply #4 on: 06/02/2010 11:15:40 »
I would think the most likely cause of power drop of is thermal expansion of the body of the magnetron tube that causes misalignment of the magnetic field.
Perhaps the manufactures of these tubes test them and sort them for this behaviour and sell the bad ones more cheaply. 

microwaveguru

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« Reply #5 on: 07/02/2010 18:08:57 »
RD's answer is correct, but there is more. There is also heating of the transformer. With all that, all microwave ovens exhibit a decease in output power with time, but it is not a constant decrease. If you start a cold oven (hasn't been used for at least 6 to 8 hours,the output power decreases by about 10% within 10 to 15 minutes and then is stable for hours. We've tested many (at least 50) ovens and they all exhibit this behavior. But all this is done under controlled laboratory conditions. In the home, there are other factors having to do with the food being heated that makes it seem as if the heating is not consistent - such things as food mass, starting temperature, shape, and lots more influence this.

Geezer

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« Reply #6 on: 07/02/2010 19:43:37 »
RD's answer is correct, but there is more. There is also heating of the transformer. With all that, all microwave ovens exhibit a decease in output power with time, but it is not a constant decrease. If you start a cold oven (hasn't been used for at least 6 to 8 hours,the output power decreases by about 10% within 10 to 15 minutes and then is stable for hours. We've tested many (at least 50) ovens and they all exhibit this behavior. But all this is done under controlled laboratory conditions. In the home, there are other factors having to do with the food being heated that makes it seem as if the heating is not consistent - such things as food mass, starting temperature, shape, and lots more influence this.

Are we being ripped off then? Are microwave ovens not actually capable of delivering the wattage they claim?

If I buy a car with a 100 HP engine that can only produce 90 HP, I usually have some recourse. (A certain car manufacturer was caught doing this not so long ago.)

chris

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Why Does A Microwave Oven Lose Power Whilst In Use ?
« Reply #7 on: 08/02/2010 08:28:31 »
Wood-burning stoves (eg for heating your living room) are similarly misleadingly rated.

Manufacturers eager to flog you one quote "max outputs" (in BTU or kW), but this is with the stove flogged to melting point, dampers fully open and burning a few shovelfuls of whatever that stuff was the mad professor in Back to the Future 3 jammed into the firebox of the steam train...

Consequently most home stoves don't come close to the manufacturers' quoted outputs.

Instead, because people were being mislead in this way, companies are now having to switch to "nominal" outputs, which is supposed to be more representative (like an average) of heat output.

Maybe microwaves should do the same...?

(Meanwhile, this thread is so interesting I might recommend it to Diana as a Question of the Week...)

Chris

neilep

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« Reply #8 on: 08/02/2010 13:50:38 »
Thanks to all for your very interesting answers.

It's the same with audio amplifiers and speakers....manufacturers know people just love those big numbers when half the time the customer doesn't even know what they mean !

Geezer

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Why Does A Microwave Oven Lose Power Whilst In Use ?
« Reply #9 on: 08/02/2010 17:08:40 »
Wood-burning stoves (eg for heating your living room) are similarly misleadingly rated.

Manufacturers eager to flog you one quote "max outputs" (in BTU or kW), but this is with the stove flogged to melting point, dampers fully open and burning a few shovelfuls of whatever that stuff was the mad professor in Back to the Future 3 jammed into the firebox of the steam train...

Consequently most home stoves don't come close to the manufacturers' quoted outputs.

Instead, because people were being mislead in this way, companies are now having to switch to "nominal" outputs, which is supposed to be more representative (like an average) of heat output.

Maybe microwaves should do the same...?

(Meanwhile, this thread is so interesting I might recommend it to Diana as a Question of the Week...)

Chris

I hope they quote them in BTU/hour, which raises an interesting question.

Why do some many industries feel the need to have there own "special" units for the power?

BTU/hour is a measure of power and can just as easily be described in Watts.
Same with horsepower.
Same with Tons (as used by the air conditioning industry in the US)
There may be more.

Edit:
Calories per second

« Last Edit: 08/02/2010 18:43:57 by Geezer »

neilep

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« Reply #10 on: 08/02/2010 19:41:03 »
My question MIGHT be QOTW !!...nywahh nywahh nywahhh nyahhh nywahh!!

*sheepy sticks out tongue and does a silly dance to taunt the Geezer*

...and..I win a prize too....a round the world 3 month luxurious cruise !..

Geezer

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« Reply #11 on: 08/02/2010 20:20:33 »
Yeah, yeah, yeah! Rotten little swot!

neilep

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« Reply #12 on: 08/02/2010 20:51:22 »
ewe can come with !!.Chris said I could bring friends and their family too !!..YAYYY !!

Geezer

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« Reply #13 on: 08/02/2010 21:30:57 »
er, well. in that case ewe is my fav swot. How much pocket money is he giving us for the cruise?

yor_on

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« Reply #14 on: 09/02/2010 01:16:17 »
I think Neil and Chris mislead you slightly there Geezer. It is well known that all Americans are millionaires (The streets are paved with gold. It's true, I saw it) so I'm guessing that you, Mr Geezer, you are the 'pocket money.. Don't act too surprised when they call you to take care of the tickets, just remember to smile..

Hey, can I come too?

neilep

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« Reply #15 on: 09/02/2010 11:47:04 »
I think Neil and Chris mislead you slightly there Geezer. It is well known that all Americans are millionaires (The streets are paved with gold. It's true, I saw it) so I'm guessing that you, Mr Geezer, you are the 'pocket money.. Don't act too surprised when they call you to take care of the tickets, just remember to smile..

Hey, can I come too?

Of course ewe can come chum..more the merrier..

erhmm..I just received a brochure about the ship !!






errhm !!


yor_on

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« Reply #16 on: 09/02/2010 19:11:29 »
Ah, perhaps Our mystical millionaire will help us with a better ship?

I'm sure they have bigger ones over there Neil. Don't just look (get stuck) at the English 'cruisers' available. As a by side we have inflatable ones in Sweden. Very nice ones too, mine is a duck.

Geezer

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« Reply #17 on: 09/02/2010 19:28:30 »
I think Neil and Chris mislead you slightly there Geezer. It is well known that all Americans are millionaires (The streets are paved with gold. It's true, I saw it) so I'm guessing that you, Mr Geezer, you are the 'pocket money.. Don't act too surprised when they call you to take care of the tickets, just remember to smile..

Hey, can I come too?

Of course ewe can come chum..more the merrier..

erhmm..I just received a brochure about the ship !!






errhm !!



At least the cabins all have an ocean view.

yor_on

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« Reply #18 on: 09/02/2010 20:27:20 »
Well, it could be a prototype?

"See the ocean beyond, join our world tour."

And. "remember to clothe yourself warmly." perhaps?

I'll bring my duck, just to be sure.

 

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