Measuring microwave wattage

So you eat a lot of microwaved beans on toast for lunch? *There's* the problem. Switch to something more palatable, such as Spaghetti-Os or Kraft "Macaroni & Cheese". Jim T. puts Merlot in his. ;-)

Cheers,

Phil Hobbs

No you need some weenies! Lyle

I have used the same idea but 2L (icecream container) and *70

If you read the above sentence verbatim, and ignore context, it sounds quite funny. I mean, how would a wave wear out? Do X-rays and short-waves wear out, too? What about UV and vis radiation?

But of course I know what you mean.

--Mac

Hey! Give Terry a break, beans on toast is a lot healthier and tastier than the usual English fare. :))

--
Tim Hubberstey, P.Eng. . . . . . Hardware/Software Consulting Engineer
Marmot Engineering . . . . . . .  VHDL, ASICs, FPGAs, embedded systems
Vancouver, BC, Canada  . . . . . . . . . . . http://www.marmot-eng.com

Added the experts group.....

The advice might be you need a frying pan, or two, and perhaps a saucpan.

(And some On!ons)

DNA

My beans on toast were not quite as hot as usual this lunchtime. I suspect that I may have damaged our microwave recently (placing a ready meal in a metallic container into it by mistake for a few seconds) so that it's no longer delivering its spec of 650 W.

The following test seems to confirm this, but I'd appreciate a check of my calculation please.

I poured 200 g of tap water into a small container. It was a thin plastic container weighing 24 g, so I've ignored its thermal mass. After a few minutes (while I fetched my DMM and a couple of temperature probes) I measured the water's steady starting temperature as 19 C. I heated it for 50 s and its finishing temperature was 43 C.

So the microwave raised 200 g of water 24 degrees C in 50 seconds.

I had to look up the Calorie/Joule relationship, which is that 1 cal =

4.1868 joules.

So wattage = (200 * 24 * 4.187)/50 = 401 Watts

OK?

I've been intending to replace this old unit with a more modern 800 W oven for a couple of years, so it looks like the time has come.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Microwaves are quite sensitive to line voltage changes. Be sure to check. But they also wear out.

Thomas

I would consider putting 2l of tap water into a large covered container, and repeating, over maybe 500s. (stir before measuring)

200g may be too little to well match.

Fourmi bruillé, old French country recipe.

John

The better cooking-ware stores around here carry miniature torches for such occasions.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

We buy the Safeway Select frozen creme bruillé and blast them with a regular propane torch... very satisfying in many ways. Even The Brat is getting pretty good at it, and it sure impresses her friends. Those foodie-store toys are to laugh at... you have to refill them from a ciggy-lighter butane thing every few desserts, and the show is much less dramatic.

I had to explain to my French friend, who is very proud of his toy blaster, that the butane is liquid so you have to point the thingie

*down* when you refill said toy. He was filling with gas and wasn't getting through two cb's before he had to reload. But then, he makes them from scratch from his grammy's recipe, so I'm not complaining much.

John

What size chicken would give the best SWR :)

Thanks. That gave me a 13 C delta, so a significant improvement to 455 W. But still well down on its 650 W rating!

The above was at 08:25 UK time, a heavyish consumption period I imagine, so I'll repeat mid-morning to see if I can nudge it up a bit more.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Can you check another unit of same ilk to see if the result is the same? Power delivered into the load may not be the 650W that's on the spec. depending on efficiencies in the oven. Nice checking though! :-)

Cheers.

Ken

In the good old days, when watts were watts and not some mathematical construct designed to sell microwave ovens and stereo amplifiers on the "bigger is better" principle, the method to measure microwave oven output went like this.

Use 1 litre of cool tap-water in a microwave safe plastic jug. Measure temperature in Centigrade. Place off centre on turntable and run on high for 2 minutes. Stir and re-measure temperature, then subtract initial measurement. Multiply temperature gain in degrees Centigrade by 35 to obtain a realistic power output.

Compare readings taken at mid- morning or late evening with readings taken at peak electricity consumption times. Significant variations in power output will indicate a mains power regulation problem. This is not an uncommon situation, affecting many older ovens that use the transformer/voltage doubler psu type. Switching type supplies are, of course, designed to compensate for low input voltage.

Once you get above a Cornish hen, I would think the density or moisture content is most important. Maybe how recently it drank prior to losing its head, or what kind of diet it was raised on. Not aware of any studies of chickens as microwave terminations (not to say there are none.)

I did do an impromptu study of the effect of ~2 GHz microwaves on the small brown ants that occasionally invade my house.

Left a plate with some sweet remnants on my counter. Came back to discover several dozen ants on it. This didn't please me so I wanted to do a mass assassination. Popped the plate into the microwave oven on high for several minutes. No effect. Happily strolling around without the slightest sign that I was blasting them with heavy energy. (Now even crawling off the plate and through the chamber. Little bastards!)

Flash of insight. Microwave ovens probably don't work well on things that are significantly smaller than 1/4 wavelength.

So if you want to fry ants in your microwave, be sure to add some water.

[Later, I found my favorite method to be a fast moving, low flame, propane torch applied in situ. No chemical residue and little damage to the surroundings with good technique.]

Hell, those Frenchpersons will cook and eat anything.

It's annoying enough when people correct my English spelling, but you can hardly expect me to type perfect French.

And the bottom still cool.

John

I did so, and got a further improvement to 520 W. That's still 20% down though, so I think a new microwave is on the cards.

BTW, assuming proportionality, that seems to imply a 7% increase in local mains voltage within that couple of hours.

--
Terry Pinnell
Hobbyist, West Sussex, UK