Measuring microwave wattage

T

Terry Pinnell

Guest
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
 
Terry Pinnell wrote:
My beans on toast were not quite as hot as usual this lunchtime.
Click to expand...
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
 
Phil Hobbs wrote:

Terry Pinnell wrote:

My beans on toast were not quite as hot as usual this lunchtime.


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. ;-)
Click to expand...
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
 
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:v0fea1hn7rl9prh1qn96nks3582qji9b5p@4ax.com...
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
Click to expand...
Added the experts group.....

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

(And some On!ons)

DNA
 
"Guy Macvon" <ilike_spam@yahoo.co.uk> wrote in message
news:91Ipe.1950$m4.1829@newsfe3-gui.ntli.net...
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:v0fea1hn7rl9prh1qn96nks3582qji9b5p@4ax.com...
My beans on toast were not quite as hot as usual this lunchtime. I


Added the experts group.....

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

(And some On!ons)

DNA


No you need some weenies!
Click to expand...
Lyle
 
On Wed, 08 Jun 2005 20:07:56 +0100, Terry Pinnell
<terrypinDELETE@THESEdial.pipex.com> wrote:

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.
Click to expand...

A small container like that probably isn't a perfect match for the
microwave field, so you might get more power into a bigger load, like
a chicken maybe. So maybe it's OK.

John
 
Terry Pinnell wrote:

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


Thomas
 
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:v0fea1hn7rl9prh1qn96nks3582qji9b5p@4ax.com...
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
Click to expand...
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
 
Terry Pinnell <terrypinDELETE@thesedial.pipex.com> wrote:
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.
snip
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.
Click to expand...
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.
 
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:v0fea1hn7rl9prh1qn96nks3582qji9b5p@4ax.com...
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?
Click to expand...
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.
 
On Wed, 08 Jun 2005 23:08:09 +0200, Zak wrote:

Terry Pinnell wrote:

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?

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

If you read the above sentence verbatim, and ignore context, it sounds
Click to expand...
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.

Thomas
Click to expand...
--Mac
 
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:mcnea11nhodbdtv8gg4kql0qotubmumogp@4ax.com...
On Wed, 08 Jun 2005 20:07:56 +0100, Terry Pinnell
terrypinDELETE@THESEdial.pipex.com> wrote:

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.


A small container like that probably isn't a perfect match for the
microwave field, so you might get more power into a bigger load, like
a chicken maybe. So maybe it's OK.

John
Click to expand...
What size chicken would give the best SWR :)
 
"JustMe" <á@á> wrote:


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

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.
Click to expand...
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
 
On Thu, 9 Jun 2005 08:23:18 +0100, "Alt Beer" <NULL@NULL.com> wrote:

A small container like that probably isn't a perfect match for the
microwave field, so you might get more power into a bigger load, like
a chicken maybe. So maybe it's OK.

John

What size chicken would give the best SWR :)
Click to expand...
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.]
 
Terry Pinnell <terrypinDELETE@THESEdial.pipex.com> wrote:

"JustMe" <á@á> wrote:


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.

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

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.

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.
Click to expand...
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
 
"Guy Macvon" <ilike_spam@yahoo.co.uk> wrote in message
news:91Ipe.1950$m4.1829@newsfe3-gui.ntli.net...
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:v0fea1hn7rl9prh1qn96nks3582qji9b5p@4ax.com...
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?

snip
Click to expand...

400 watts out of 650 available into one measly cup of water seems pretty
good to me. Probably generated a bit of steam too so you could weigh your
cup before and after to find out what that was and guesstimate what used to
be called latent heat of vapourisation or something. Better still nip round
to your next door neighbours and cross-check on her machine.
The advice might be you need a frying pan, or two, and perhaps a saucpan.

(And some On!ons)

Best of Luck - Mike61/2
Click to expand...
 
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.

--
Click to expand...
I don't think there is anything very linear about the transition from
partial power to full power related to mains voltage. About as linear as a
zener knee if you get my drift.

In general, modern magnetrons do not fail gracefully as yours would seem to
indicate. They sometimes fail short circuit internally, or more commonly
where the feed-through filter capacitors are built into the base connector
assy. A blown short protector diode and line fuse is the usual result.

You may want to ponder a little more before you consign your old friend to
the municipal tip. If the magnetron has developed a partial internal fault
the power that is directed into it is transformed to heat instead of
microwaves. This can be detected as a sort of run-away effect in the air
blown through the cooling fins. The longer you run it under load, the less
output you get and the hotter the exhaust air stream. Pretty easy to spot.


Common causes of low output power, not related to mains supply, can be
intermittent spade connections to the magnetron base, (there are 10 to 20
amps at low voltage driving the filament) or overheating of the magnetron
caused by fluff blocked cooling air intakes to the cabinet. These are
usually on the bottom plate and rarely seen.

Most on this newsgroup will have some idea what a few kilovolts at half an
amp will do, and the potential for a sneak attack by the doubler capacitor.
It is usually permanent. Take great care.
 
On Thu, 09 Jun 2005 09:52:26 GMT, rex <notat@hotmail.invalid> wrote:


[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.]
Click to expand...
Fourmi bruillé, old French country recipe.

John
 
On Thu, 09 Jun 2005 07:53:45 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Thu, 09 Jun 2005 09:52:26 GMT, rex <notat@hotmail.invalid> wrote:


[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.]


Fourmi bruillé, old French country recipe.

John
Click to expand...
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.
 
On Thu, 09 Jun 2005 07:55:29 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On Thu, 09 Jun 2005 07:53:45 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Thu, 09 Jun 2005 09:52:26 GMT, rex <notat@hotmail.invalid> wrote:


[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.]


Fourmi bruillé, old French country recipe.

John



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

...Jim Thompson
Click to expand...

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
 
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