Microwave plate turn direction change. Why?

[clayton_e]

I don’t really know a better way to phrase it than that…

I’ve noticed microwaves often have their rotating plate change direction after you stop it for a second to see if something is done then start it again.

Why?

I understand that having the plate turn puts the food item through as many microwaves as possible and from many angles, getting rid of small spots that would be cold by missing the microwaves… But changing direction while turning would have no effect on that… would it?

[MC_E]

I don’t have a cite, other than the quote below, but I know that I have read that the direction the motor turns is random.

A motor with a completely symmetrical stator will start and run in seemingly random directions, as the armature will turn towards whichever pole of the stator is nearest when it last stopped. In an application where the direction of rotation matters (and that’s most motor-drive applications), stators are built such that the rotor will always be attracted the same way, and thus start and run in the same direction.

[Q.E.D]

The type of motor used is called a synchronous induction motor and unless there is a mechanical means to prevent it, the motor will randomly start in either direction. Due in large part to the energy-storage properties of the the geartrain, the motor more often than not starts in the opposite direction it was running before. Since oven turntables are one of the few applications where motor direction is unimportant, microwave oven manufacturers can save money by using this less expensive type of motor.

[clayton_e]

Well thank you both much. This Q has been Aed, so I guess this can be closed.

[Frylock]

@MC$E

I don’t have a cite, other than the quote below, but I know that I have read that the direction the motor turns is random.

What’s that a quote from?

-FrL-

[MC_E]

@Frylock

What’s that a quote from?

-FrL-

I am pretty sure it was from ask.metafilter.com. I don’t have the exact page in my history on this machine though.

[Napier]

Just tried my microwave, and it seems to pick a direction randomly, not alternately.

[clayton_e]

I’m sure I didn’t notice it when it would go the same direction it just did… So perhaps it isn’t alternating. I just know a good chunk of the time when I check on something to see if its done then put it back in for a few more seconds it will go the opposite direction.

[Nanoda]

Hmm. The microwave here at my house (a small, cheap brand probably, came with the place) appears quite random, and exhibits gear lash and other motions I would classify as indicative components such as Q.E.D. describes.

However, from prior testing at the office (don’t ask), I determined a few months back that the microwave table there would always turn twice counter-clockwise, then once clockwise. I don’t have an explanation for this, other than someone was asked to make it either ‘random’, or ‘alternating’, and screwed it up.

[clayton_e]

@Nanoda

However, from prior testing at the office (don’t ask), I determined a few months back that the microwave table there would always turn twice counter-clockwise, then once clockwise.

And I thought I was bored…

[MC_E]

@Nanoda

Hmm. The microwave here at my house (a small, cheap brand probably, came with the place) appears quite random, and exhibits gear lash and other motions I would classify as indicative components such as Q.E.D. describes.

However, from prior testing at the office (don’t ask), I determined a few months back that the microwave table there would always turn twice counter-clockwise, then once clockwise. I don’t have an explanation for this, other than someone was asked to make it either ‘random’, or ‘alternating’, and screwed it up.

Did you always use the same cook time when performing the test? To get a truly accurate result, you would need to randomize the cook time.

[si_blakely]

I thought it was to stop the food from getting dizzy…

Si

[Dinsdale]

Man, I would’ve sworn mine changed direction every time it was stopped and restarted. Also thought each time it was initially started it went the same direction (counter clockwise I think.) Will have to pay more attention. (Hey - looks like I have a NY resolution!)