Cook - carosel rotates clockwise.
Cook - carosel rotates counter-clockwise.
Every start or restart results in a change of direction.
Was the designer worried that the food would get dizzy?
Mine does.
Beats me. Might make a good GQ question.
The one at work has the annoying feature that it carries on cooking when the timer has ran out.
Nah. Mine just sits there. I have to drink until the kitchen spins. 
Hum, mine does too. I always thought it was so the rotating part doesn’t wear out or something. Now I wonder.
I’m feeling too lazy to search, but that reversing is more a quirk of cheap motors than any actual intent - the motor doesn’t have a strong “instinct” to start rotating in any particular direction, so it just starts spinning and it’s up to fate and the particular phasing of the incoming electricity to determine which way it goes.
But it’s 110V.
Mine does it too.
Mine does it as well. Without giving it much thought, I had just chalked it up to some attempt to have the food cook more evenly. Now that I think about it, I realize that idea is kinda silly.
So it’s either A) an attempt to appear like a useful, even-cooking feature, or B) something else that none of seem to be aware of.
Wow…what a spectacularly unhelpful answer.
I don’t see why that matters; what matters is that these are AC motors. When the motor is started, the direction depends on the position of the magnet and which way the AC current is bouncing when you turn it on. So there’s a 50/50 chance of which direction it will go.
There are ways to build AC motors that always go the same way, of course, but they’re more complicated. and Since the direction doesn’t matter for microwaves (or laundry dryers,) the simple random-direction motors are used.
It probably stops in front of you, if you let it rotate for a minute too!
Well, since 110 is single phase and switching the back and white wire won’t change rotation I didn’t know about the that the postion of the internal magnet comes into play. Thanks for the heads up.
btw, our electric dryer alwas travels counterclockwise.
There’s obviously variation between models, and the microwaves I’ve taken apart over the years haven’t all used the same type of drive system, so the fact that most/all rotating microwave carousels reverse probably isn’t an accident. It may have started as one, but I think any engineer would capitalize on this effect once they noticed it.
I don’t think the position of the magnet is relevant, because it would only yield a reversal 1/2 the time. Similarly, I doubt the initial phase of the electricity doesn’t dictate the direction because a) its effect would depend on the random orientation of the magnet, resulting in 50% reversals; b) the initial impulse would be very brief (no more than 8.3 milliseconds) and often very weak (the initial amplitude is near zero for about 20% of the cycle)
All these factors would tend to make the startup direction random (50-50), but my current microwave reverses its previous direction 90+% of the time, and I’ve never had one that reversed less than ca. 75% of the time.
I think the reversal in direction is caused by inertia and hysteresis (“wiggle room” or “slack”) in the mechanical system. Try this:
When the motor stops, the inertia of the food will continue turning the platter in the direction it is going, in effect forcing the platter/hub/motor to the limits of its hysteresis in its direction of motion. You can do this manually --in either direction-- and the next time you turn on the microwave, it will usually go in the direction opposite to the the direction you pushed it not the opposite to the direction in which it was turning.
At least that’s how it works on mine.
Mine does this, but it has an additional feature I like even better: one complete rotation is exactly 10 seconds. Thus, when I nuke my coffee water in a Pyrex cup with a handle, if I set the timer for any multiple of 10 seconds the handle always comes back around to the same position as the one I set it in.
OK, so maybe I’m easily impressed, but I think that’s neat.
Actually, if it rotated three times widdershins, it would summon Satan, so they engineered a fix to avoid that.
Neat, huh?
[QUOTE=jdc]
Cook - carosel rotates clockwise.
Cook - carosel rotates counter-clockwise.
[QUOTE]
You don’t list your location. If you’re close to the equator, it could be due to lack of coriolis force 
My microwave rotates clockwise all the time as does my dryer. I run a tight ship :rolleyes:
I’ve noticed ours goes both ways, but I’ve never really kept track at the frequency. I doubt I could get my wife to cooperate with a logbook, anyway.
I expected this thread to be about the burn popcorn button.
Actually they aren’t all that much more complicated. All you have to do is wind a shorted turn or two around the field core, or part of it, in order to have a motor that always starts in the same direction. This makes a “split-phase” induction motor and is used in clocks, small fans and many other places.