So, just how powerful is that Microwave??

[kb0nes]

I have several different microwave ovens I use on a regular basis, both vintage and modern. I have noticed marked performance differences between them. So I wanted to attempt to measure the actual output power of each oven.

Its actually a simple procedure to just measure the heating of a known quantity of water in a defined amount of time. Years ago a calorimetric power test like this was done to measure transmitter power on UHF and higher frequencies where availability of accurate meters was limited.

The math to derive wattage is actually pretty simple, here is the formula:

Power(watts) = Vol of H2O(ml) x Temp Rise(C) x 4.187 / Time(sec)

For the curious the 4.187 constant is the conversion from calories to watt seconds. One calorie is needed to raise a ml of water 1 degree Celsius.

Here is a photo if the 1984 Whirlpool microwave used for this test. The next couple posts will show the simple process.

 

[kb0nes]

Known Volume of Water

First off find a microwave safe container. I used an old 1 gallon milk jug since it has very little thermal mass to induce error in the results.

1 milliliter of water happens to weigh 1 gram (coincidence eh?) so I just used a postal scale. The jug weighed 66 grams which I normalized out with the Tare function.

Photo shows the jug with 1,000 grams of water. If you don't have a scale you can measure 1000ml or 33.8oz.

 

[kb0nes]

Starting Temp

Using a thermometer record the starting temperature of the water. Ideally the water should be in the 20 deg C range to prevent it from getting too hot when its heated. If we get close to the boiling point then the temperature change goes non-linear.

In my case I had to lay the jug on its side to fit in the oven cavity.

Starting temperature is 25.3C

For this test I chose to run the oven for a total of 200 seconds (3:20) total time. The greater the volume of water and the longer the run time the more the variables are normalized. Things like thermal mass of the jug and warmup time of the Magnetron etc.

 

[kb0nes]

Ending Temp

was 53.5C for a temperature rise of 28.2C for this oven over the 200 second run. Its important to stir or agitate the water a bit before taking the final reading, warm spots can stagnate skewing the results.[this post was last edited: 7/9/2014-19:04]

 

[tomturbomatic]

This is a report in progress.

 

[kb0nes]

So plugging all that into the formula:

(1000ml x 28.2C x 4.187) / 200 = 590 watts which seems a bit low but is believable.

Out of the three microwaves I use this one seems to be the slowest. The Panasonic Inverter model I repaired a couple years ago is WAY faster.

If input power was measured while doing this test then efficiency (or lack thereof) could be easily measured.

This test could be easily duplicated and results should be pretty repeatable. It would be interesting to hear how some of those really vintage microwave ovens stack up against the more modern units too. If anyone else bothers to try this at home please post your results!

 

[pcasa]

radarange

I love all my Amana Radaranges - but they suck at popping popcorn

 

[xraytech]

Paula,

I think microwave popcorn can be harmful to your microwave oven.

Besides popcorn tastes so much better stovetop or from a vintage popper

 

[jeffg]

What's strange imo is that there doesn't seem to be much relation between output wattage and actual cooking performance. E.g. a 1980 Panasonic was our daily driver for 30+ years (until it finally developed door latch problems). and according to specs it's only a 700W unit. But frozen food cooked according to package directions comes out perfect, while the 1200W inverter Panasonic unit we replaced it with produces frozen food badly overcooked at the edges, and/or underdone in the middle. Even when power output is reduced to what should be the same or similar as the 700W. The two units are very similar in design (size, turntable etc) so we're at a loss to explain it.

 

[kb0nes]

Jeff,

With actual food in the cavity energy distribution is likely to be every bit as important as output power. Especially frozen food which is difficult not to over cook the outsides and thin sections while still leaving the middle frozen.

Heating water is easy since the the convection in the fluid minimizes temperature variations. Also with that much water in the cavity the loading is very uniform which may not be true with a piece of frozen food in there.

The way older microwaves controlled their output by pulsing the magnetron is actually beneficial for defosting since it allowed dwell time for heat to conduct through the food. Modern inverter units that modulate actual RF levels may have more uniformity issues defrosting frozen foods.

I was only trying to test ultimate power, trying to test actually cook-ability is an entirely different and deep can of worms! I'll let someone else sort that out...

 

[jeffg]

"The way older microwaves controlled their output by pulsing the magnetron is actually beneficial for defosting since it allowed dwell time for heat to conduct through the food. Modern inverter units that modulate actual RF levels may have more uniformity issues defrosting frozen foods."

Thanks for the info. It explains a lot of online user reviews for microwaves.

 

[earthling177]

Jeff, I don't know your old microwave, but a lot of older nukers had a stirrer fan in lieu of a carrousel tray to distribute the microwaves. Some of the first nukers to have the rotating tray (to improve cooking uniformity) also kept the stirrer fan and those machines cooked very evenly.

When the bean counters removed the stirrer fan to save a buck or two, it became obvious to me that just the rotating tray doesn't cut it, but most people don't clue into it because they just use the nukers to rewarm food and make pop corn, while people who actually want to use the machine to actually defrost and/or cook are few and far between.

 

[jerrod6]

Can't we just look at the label on it?

 

[whirlcool]

I believe our old Litton was 750W and it was a pulser. You could see the fan on top rotating throught the translucent shield in the top of the oven cavity. It was fast for it's time.

Now our 2008 GE microwave (1100W) is much faster, but it's a pulser too. You can see and hear the pulsing with the light dimming/brighter. We really like this oven. It's an over the range oven and even though it's been in daily use for six years the thing still looks like new, it sparkles! What I like best about it is that the turntable platter and the little ring it rides on can all go in the dishwasher for cleaning! And just boil some water with vinegar and lemon juice and the thing cleans up just by wiping it out.

 

[kb0nes]

Can't we just look at the label on it?

Sure we can... But it only tells you the average power consumed, it may or may not correlate well with the RF power into the cavity. Efficiency levels vary with differing circuitry and there is always the possibility that something has failed in a given unit.

I'm especially hoping that we can see some tests run on the earliest vintage microwaves, like some of the 900Mhz microwave/electric resistance combo ovens. I'd love to get an idea on the output of those beasts.

 

[wayupnorth]

My 1979 Whirlpool looks similar. It is a Mark Series, has 3 cooking cycles, probe etc., that I never use along with the huge harcover cookbook that came with it. It says output 350 watts. I use the minute timer, clock keeps perfect time, set it at 1 minute start. If its not warm enough, repeat. Thats what I have done for 35 years.

 

[pcasa]

the "pulsating"

.. just a funny to share - before I changed out the power panel in my 1955 house and upgraded the electrical service from the pole - my entire house would "pulsate" when I ran the Radarange on defrost - you could stand outside and watch the house lights slightly dim - then bright again rhythmically - hahahahahahahhahahahahaha

 

[kb0nes]

Just repeated the test on my home over the range KitchenAid microwave.

Results of two runs averaged 693 watts calculated.

Model tag says 700 watt output. Assuming the appliance is in good shape that validates the test. I would have estimated this oven to be about 20% better then the first one I tested in this thread.

 

[gansky1]

Very interesting thread, Phil, as always!

I will give this test a go in the Hotpoint micro-range over the weekend when I have some time.