How long does it take a microwave oven to warm up?

micky explained on 11/30/2016 :

The energy transfer is nearly immediate. The oven only warms up because of the food warming up.

Some items which I microwave would end up having cold or cool spots, so I used to cook say a three minute item by cooking for two minutes and then allowing the heat to spread for a couple of minutes, and then zap for another minute or so.

I now have a new microwave oven with a turntable (the other had a reflector) to help avoid the spottiness. The ovens power output is also an important factor to consider.

When you get down to thing that only take a few seconds, the fact that it takes about two seconds for the magnetron filament to warm comes into play.

Usually you can hear the fan slow down once the microwaves are really being produced.

The heater in the magnetron tube takes a couple seconds to warm to the point where it will emit electrons. You can hear it easily on the old transformer microwaves, the fan starts and it begins to hum, then a couple seconds later the hum gets much louder. That louder hum is when the magnetron tube starts conducting.

Newer microwaves with switching power supplies may delay turning on the HV until the heater has warmed up, and they may not have that transformer hum, so it may be harder to tell when the RF comes on.

Jon

I find it easier to microwave for longer periods of time at a lower setting to get even heat.

It takes a few seconds to heat the filament of the vacuum tube. So, it's advisable to use longer times, but NOT lower setting (which just adds multiple ON/OFF switching to the problem).

To get something a 5 second zap, you might be well advised to put a cup of water in next to your nibble, and give the pair ten seconds. The water load will slow the nibble heating, and the longer time means the turnon variability is less important. It also gives your turntable a chance to do a full revolution under full magntron power (better hotspot control)

Stick an old CD in the MW and you can see exactly when the RF power starts.

Yes, the new MW oven has programmable settings for power level and rest periods and such for better results. The old one only had a single knob with minute marks on it and a bell that softly, almost inaudibly, went 'click' when the time expired.

The old one is 26 years old, but it still works.

setting to get even heat. "

Yeah but they generally only turn it on and off. The duty cycle controls the power level.

I have only see one microwave in my life that actually had separate taps on the transformer for lower power.

Really. Never thought of that.

+1, You are the only one who did not lambast the OP for using the term 'warm up' to mean 'cause the ambient MW intensity to reach its operational range'.

When I am judging time for extremely small loads (like softening butter without liquifying it), I allow 4 seconds for my oven.

I find that the hum does not get louder though. Instead, I notice that the fan speed lowers a bit, presumably because the supply voltage for the fan is then being loaded down by the power consumption by the magnetron.

I had an Amana Model 2, that looked just like the drawings of microwaves that were used for decades. It lasted many years. I got it used around

1975 and met its earthly demise around 2000. . Although the insulation on the diodes had failed** and it sparked, so I covered the open parts with GE silicon sealant, and something else I fixed, and eventually the power transformer broke, I think it was. They wanted 300 dollars for it and my pointing out that they should take 80 since I coudl buy a new one for 80 didn't help. They lowered the price to the repairmans price of 200 roughly.

**Amanda didn't want to send me a schematic. I had to beg, and promise I knew what I was doing and wouldn't kill myself. She relented.

I'll go with "a couple". Thanks.

That sounds like it might work

Sure. That's what I had in mind.

I'll pay more attention.

Thanks and thanks all.

Good idea. Another way would be to cram a wad of paper between the door and the oven, and use a microwave leakage detector to measure the resultant leakage. It there's a slow rise in output, you'll see it on the meter, which you won't see on the CD.

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Micky,

Heating improves the physical "eatability" of products and also beats the crap out of bacteria. If you cook for under the prescribed time to suit your tastes then you need to understand about the bacteria.. Don't poison yourself. Sorry, can't help you with cooking times.

Dave M.

YIKES!!

This is a single question with two separate answers.

a) Less than 4 seconds for the magnetron tube to reach full output. There w ill be a sequence as others have noted: Fan-Start, relay click, magnetron s tart.

b) Then, it depends. We have a 1,100 watt Panasonic that is very fast-cooki ng to the point that we are very careful of the setting as even 10 seconds makes a difference. A 500-watt device will provide an entirely different ex perience.

So, it is a combination of the onset time and the actual power of your micr owave that will give you the answer. But what is obvious is that 2 @ 5 seco nds is NOT 1 @ 10 seconds. The reality is that a 5-second setting will give ~1~2 seconds of actual full-output heat. 10 seconds will give ~6~9 seconds .

Peter Wieck Melrose Park, PA

Pan fry your egg rolls, roll so four sides get crispy. Microwaved egg rolls just aren't worth eating. IMHO Mikek

[snip]

I have an older microwave, that has only 700W. Most directions are for higher power. I find most things are OK if I add 25% to the cooking time. For example, if it says 3 minutes I use 3:45.

BTW, some people have said that if I got a new microwave, it would probably fail before the old one.

[snip]

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Mark Lloyd 
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"If fascism ever comes to America, it will be wrapped in the flag and 
carrying a cross." -- Upton Sinclair, Huey P. Long, and others.

[snip]

I have a 30 year old JCPenney microwave (from the time they sold a lot of things rather than just clothes and related stuff).

--

24 days until the winter celebration (Sunday December 25, 2016 12:00:00 AM for 1 day).

Mark Lloyd

"If fascism ever comes to America, it will be wrapped in the flag and carrying a cross." -- Upton Sinclair, Huey P. Long, and others.