Why do microwaves shut off 15 seconds early?

[James Wilkinson Sword]

My microwave turns off the magnetron 15 seconds before the end of the timer. What's the reason for this?

[alan_m]

How does it manage a 10 second blast?

[James Wilkinson Sword]

It only does the 15 second shut off for longer times. Definitely on a 10 minute run.

[Brian Gaff]

I think this only happens on lower than full power settings. This is because a Magnetron has no power setting and the power is derived from the duty cycle of ons and offs and often the off time is in work when the timer ends. Brian

[Max Demian]

Do you mean it pings/beeps and the light goes out at the 15 second point? I assume you have a fancy microwave with a digital timer rather than a simple rotary knob like mine. All the same, I think mine stops at the correct time as far as I can tell.

[James Wilkinson Sword]

No, mine will do that too on low power, cycle on and off during the whole cooking time. But this is on full power I'm getting the 15 seconds off, only at the end. I hear the magnetron stop, and I've noticed the power consumption drops to almost zero (just enough for the light, fan, and turntable motor).

Testing.... doesn't do it on 1 minute cooking time. Or 2 minutes. It does do it on 5 minutes and 10 minutes.

Perhaps it's to allow frothed up food to calm down before the user takes it out?

I noticed something else while testing. It uses 1.45 kW to start with, then gradually lowers to 1.25 kW. I thought at first it was being clever and lowering the power as the food got hotter so it didn't boil over, but starting another cooking cycle with cold water or with already hot water changes nothing. It seems to use less power when the oven itself is warmer. The magnetron gets more efficient or tired perhaps?

[James Wilkinson Sword]

Yes it's a digital one. If I set it to cook on full power for 10 minutes, it runs the light, fan, turntable, and magnetron for 9 minutes 45, then the magnetron goes off but everything else still running for 15 seconds, then it shuts off fully and bleeps.

As I said to Brian:

It doesn't do it on 1 minute cooking time. Or 2 minutes. It does do it on 5 minutes and 10 minutes. Perhaps it's to allow frothed up food to calm down before the user takes it out?

I noticed something else while testing. It uses 1.45 kW to start with, then gradually lowers to 1.25 kW. I thought at first it was being clever and lowering the power as the food got hotter so it didn't boil over, but starting another cooking cycle with cold water or with already hot water changes nothing. It seems to use less power when the oven itself is warmer. The magnetron gets more efficient or tired perhaps?

[Graham.]

Perhaps you are looking at the question the wrong way, and you should be asking "Why does the cooling fan (and light) continue to run after the magnetron turns off", that would of course be a sensible thing to do. You, as a manufacturer might also want to create the illusion that these 15 seconds are included in the cooking indicated time and not tagged on afterwards as some users would correlate the fan noise with the "nuclear death rays" inside.

Did you know that no microwave radiation is produced for the initial 3 seconds of the indicated cooking time, as it takes that long for the magnetron to warm up?

[Bob Minchin]

Yes I was wondering that too.

[James Wilkinson Sword]

Doesn't sound sensible to me. Once the cooking is done, the whole thing should shut off. And if it's going to blow steam out for a bit, it should still bleep to tell the user they can take the food.

So the user is actually cooking the food for less time than they think? That's insane.

Since the death rays switch off as soon as the door is opened, what's the problem? If I take the food out early, I just open the door, I don't press "cancel" first. I recently used my neighbour's oven when I was round there, and was surprised to find the damn thing came back on (empty) when I shut the door afterwards! I think it was one of those antique things with a mechanical dial.

3 seconds isn't much, but 15 is.

[James Wilkinson Sword]

It's usually the dish that burns my fingers, not the food. A lot of crockery seems to contain something that absorbs microwaves, and ends up hotter than the food.

[Mr Pounder Esquire]

Hucker is trolling. It really is best to ignore the turd.

[Graham.]

That's right, but it wouldn't be the first time a kitchen aplience has told me lies. I had a Bosch fridge freezer with a control panel that was perfectly capable of indicating the tempratures with a resoluton of 1 C deg but it waited until there was a change of 5 C degs before updating the displays.

[James Wilkinson Sword]

Sounds faulty to me, I can't see Bosch making something that shit.

[fred]

mine does the exact same thing ,,,, on high power ...

[Fredxx]

I strong recommend you read this before you reply again to to a 3 year old post:

[Brian Gaff (Sofa]

Yes that is a relatively young post, I've seen them go back over 10 years simply because the platform being used sorts by date but seems to not care about years. Incidentally, I'd dispute the actual content in that message, some may well do that but mine does not. Brian