Microwave oven testing

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rscole86

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#296189 28-May-2022 17:54

I suspect my microwave oven is not heating foods as quickly as it use to.

I was wondering if the JIS test has been used by anyone else here, and any comments on how accurate or reliable it is?

Using two Pyrex jugs and a digital kitchen thermometer, I get 840w from a potential 1100w.

Mehrts

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#2919819 28-May-2022 20:15

Never heard of it, but good to know there's a basic way to determine power output that any layman can carry out.

Clima

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#2919831 28-May-2022 20:51

I have done it but used light plastic bowls. Pyrex jugs have a high thermal mass and use up quite a bit of heat. Measure the water quantity by weight. A good thermometer is needed - the accuracy of the difference measurement is critical.

rscole86

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#2919836 28-May-2022 21:01

I didn't consider the thermal mass of the glass. I'll need to see if I have any plastic that'll hold 500ml.

I made sure to weigh the water the first time.
The meat probe style thermometer goes to the nearest tenth of a degree.

SomeoneSomewhere

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#2919838 28-May-2022 21:15

Thoroughly stirring the water before measurement is also important, both when checking cold & hot temperature. The microwave pattern causes uneven heating and if you put the thermometer in a section that received less (or more) heating, you will get an inaccurate result.

The same can apply to the cold water temperature. Water that was sitting in the tap is likely at a different temperature to that in the pipes in the wall, which might be different again to that buried in a slab or in a ceiling space. And of course, allowing the water time to cool before measuring will also skew results.

Low line voltage caused by excessive voltage drop or poor connections can apparently also cause reduced power output.

rscole86

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#2919839 28-May-2022 21:30

Thanks for the tips. I'm using room temperature water, so it's consistently around 18 degrees.

I did stir the water post heating and didn't get a variation between the top/bottom of the jugs.

I'll do the test again with plastic and make sure it's all thoroughly mixed.

rscole86

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#2922583 4-Jun-2022 12:47

I've re-run the test, using plastic containers and get 899w.

So it appears I do have an underperforming microwave, but it's around 15 years old, so I think we've had a good run.