My microwave turntable turns in a different direction randomly

[PlanetJosh]

And it get's on my nerves or makes me giggle sometimes. It's not going to drive me to drinking or anything but it's just annoying to see it do that. It turns clockwise one time, then the next time I use it it turns counterclockwise.

It doesn't change direction while cooking. I didn't mean it like that in the title. Just changes direction the next time I cook with it. But not everytime, just randomly. Apparently most microwaves have their rotating mechanisms built that way because it's to expensive to make the turntable turn in the same direction.

 

[futurefields]

Put it on YouTube.

 

[Fritzo]

Mine does that too. Is it a Kenmore by chance?

 

[CPA]

LOL, why does it annoy you? Also, why are you watching your food turn in the microwave? That's like watching paint dry.

 

[balloonshark]

Mine does it too and I have a GE. I haven't really noticed it being random but it does alternate directions when I pause it during cooking. It also keeps telling me to kill my neighbors

 

[William Gaatjes]

I think it is because it is a very simple synchronous motor.
I think it depends on what the phase is of the ac line at the moment the motor is powered.

 

[skull]

I think it is because it is a very simple synchronous motor.
I think it depends on what the phase is of the ac line at the moment the motor is powered.

Makes sense why spend extra on a shaded pole or PSC if it doesn't matter what direction it goes.

Here I thought they did it on purpose like rotating a different direction after the stir would help it cook more evenly but that doesn't make much sense after actually thinking about it.

 

[BUTCH1]

I have seen several microwaves do this, as long as it's moving I would not worry about it. I still use a Tappan microwave I bought new in '83 for $250, it has no turntable!. I used an add-on called "micro-go-round" for awhile until it broke, now I just turn it around 180 halfway through cooking time.

 

[BoomerD]

Dude...the rubber band has to unwind once in a while...

Apparently the OP is new to microwaves...the ones we've had for the past 15-20 years have all done this.

 

[SOFTengCOMPelec]

I think it is because it is a very simple synchronous motor.
I think it depends on what the phase is of the ac line at the moment the motor is powered.

+1.

It might also be a simple type of stepper motor.

My Microwave(s), have done this.

It "MIGHT" be on purpose. So that it spins in BOTH directions, for mechanical reasons, to improve the mechanical life, or something. (Guess).

I.e. If it always turned in the same direction, the same points would wear out (mechanically), potentially giving a reduced life, compared to spining in BOTH directions (randomly).

But it could easily be to save money in the parts cost of the Microwave, as suggested by the post I put at the top.

It MIGHT also be an unblocking/un-jamming mechanism. I've seen that it rotates in both directions, when jammed. E.g. The cooking container FALLS out of place badly, blocking stuff in the Microwave. It seems to just oscillate between the two positions it can move to, rather than continually trying ONE direction, and potentially burning the motor out, or something.

 

[William Gaatjes]

+1.

It might also be a simple type of stepper motor.

My Microwave(s), have done this.

It "MIGHT" be on purpose. So that it spins in BOTH directions, for mechanical reasons, to improve the mechanical life, or something. (Guess).

I.e. If it always turned in the same direction, the same points would wear out (mechanically), potentially giving a reduced life, compared to spining in BOTH directions (randomly).

But it could easily be to save money in the parts cost of the Microwave, as suggested by the post I put at the top.

It MIGHT also be an unblocking/un-jamming mechanism. I've seen that it rotates in both directions, when jammed. E.g. The cooking container FALLS out of place badly, blocking stuff in the Microwave. It seems to just oscillate between the two positions it can move to, rather than continually trying ONE direction, and potentially burning the motor out, or something.

This is a property of single pole synchronous motors. They have little torque and blocking them will make them go turn the other way. The rotor just tries to follow the field. To be honest, no idea how to visualize that though , making it go both directions..

Now that you mention it, this might be a deliberately chosen property since this makes sure the food keeps turning around even if it blocks all the time.
The food still gets turned. Great choice of motor of the inventor.
It is also nice that the turntable motor does not try to wreck the inside of the microwave because it has too much torque.

 

[SOFTengCOMPelec]

This is a property of single pole synchronous motors. They have little torque and blocking them will make them go turn the other way. The rotor just tries to follow the field. To be honest, no idea how to visualize that though , making it go both directions..

Now that you mention it, this might be a deliberately chosen property since this makes sure the food keeps turning around even if it blocks all the time.
The food still gets turned. Great choice of motor of the inventor.
It is also nice that the turntable motor does not try to wreck the inside of the microwave because it has too much torque.

I agree, it is a synchronous motor. I've NOT seen a Microwave motor in a very long time, so had to guess on the motor type, without actually knowing. It seemed like a very simple, low end stepper motor (from watching my Microwave cook, sometimes). But that was an educated guess, rather than a known fact. Sorry!

As my original post was trying to say, I think it is a liked/intentional feature, that it reverses direction if blocked, rather than potentially wear itself out, and cooking the food in the same place, which is bad.

EDIT:
It's the turbine smoothness and kind of regulated movement, patterns. Seem to have psychologically fixated a type of "Stepper Motor", idea in my head. Sorry if you felt I was disagreeing with you.

 

[Newbian]

Maybe it's part Australian and spins both ways.

 

[William Gaatjes]

I agree, it is a synchronous motor. I've NOT seen a Microwave motor in a very long time, so had to guess on the motor type, without actually knowing. It seemed like a very simple, low end stepper motor (from watching my Microwave cook, sometimes). But that was an educated guess, rather than a known fact. Sorry!

As my original post was trying to say, I think it is a liked/intentional feature, that it reverses direction if blocked, rather than potentially wear itself out, and cooking the food in the same place, which is bad.

EDIT:
It's the turbine smoothness and kind of regulated movement, patterns. Seem to have psychologically fixated a type of "Stepper Motor", idea in my head. Sorry if you felt I was disagreeing with you.

You don't have to apologize, my writing style can sometimes be a bit cold and harsh. But that is because English is not my native language and when trying to remember all the technical terms to make a proper sentence without typing errors, i usually forget to write with a little feeling. I use google a lot to look up how to correctly spell and write words.

 

[Kaido]

NYT to the rescue:

http://www.nytimes.com/2013/04/16/s...rowaves-turntable-switch-directions.html?_r=0

This explains why it's random:

Q. Why does my microwave’s turntable switch directions when I stop it and start it again? Does it affect how the food heats?

A. “The direction of rotation should have no effect on the rate of heating or uniformity of heating for any conceivable food-heating situation,” said Ashim K. Datta, professor of biological engineering at Cornell University.

Rather, the reversal has to do with the relatively inexpensive turntable motors designed for use in most microwaves, said Robert J. Thomas, professor of electrical and computer engineering at Cornell. By design, they reverse their direction of rotation if a load greater than their output torque, or twisting force, is present, he said.

“All motors require a starting torque in order to start themselves from zero rotation speed to design speed, with or without a load attached,” Dr. Thomas said. It takes very little torque to rotate the turntable once it is turning, he said, but it can take several times the running torque to start it.

After a full stop, the drive mechanism is usually pressed against the load in the direction of the last rotation. When the motor encounters the load, it reverses itself and gets a small running start (with no load for a small fraction of time) to pick up speed before engaging the load again.

The mechanical linkage needed to perform this is much cheaper than the additional windings of copper wire that a stronger motor would require, Dr. Thomas said.

 

[William Gaatjes]

NYT to the rescue:

http://www.nytimes.com/2013/04/16/s...rowaves-turntable-switch-directions.html?_r=0

This explains why it's random:

they reverse their direction of rotation if a load greater than their output torque, or twisting force, is present,

This is key. But what is the physics behind it ?
It is a single pole ac motor and i think it depends when the load increase happens and what phase the voltage of the ac line is at that moment : The magnetic field direction in the stator. rotor is pulled either way.

 

[SOFTengCOMPelec]

This is key. But what is the physics behind it ?
It is a single pole ac motor and i think it depends when the load increase happens and what phase the voltage of the ac line is at that moment : The magnetic field direction in the stator. rotor is pulled either way.

This EEVblog forum has some discussion about it HERE.

It includes photo(s) and datasheet(s), and some discussion about it.

 

[purbeast0]

does spinning the stuff in the microwave even do anything anyways? i mean the stuff in the center is always going to be in the center, and the stuff further from the center is always going to be further from the center.

and the shit in the center of hot pockets is 100% going to burn the shit out of your mouth no matter whether it spins or doesn't spin while you cook them. and if you wait too long to let them cool down, they taste like shit!

 

[NikolaeVarius]

does spinning the stuff in the microwave even do anything anyways? i mean the stuff in the center is always going to be in the center, and the stuff further from the center is always going to be further from the center.

and the shit in the center of hot pockets is 100% going to burn the shit out of your mouth no matter whether it spins or doesn't spin while you cook them. and if you wait too long to let them cool down, they taste like shit!

Standing waves. Food isn't perfectly symmetrical nor are people able to place food in such a way that it will only spin on its axis of symmetry.

 

[sdifox]

It does that when nsa turns on listening mode and you decide to use the microwave at that time.

 

[Ichinisan]

I think it is because it is a very simple synchronous motor.
I think it depends on what the phase is of the ac line at the moment the motor is powered.

Yeah. I've read about this "randomness" and thought everyone was familiar with it.

 

[notposting]

LOL, why does it annoy you? Also, why are you watching your food turn in the microwave? That's like watching paint dry.

You probably aren't a fan of the front loader's secret entertainment option. The Laundry Channel, spin at 11.

 

[notposting]

I have seen several microwaves do this, as long as it's moving I would not worry about it. I still use a Tappan microwave I bought new in '83 for $250, it has no turntable!. I used an add-on called "micro-go-round" for awhile until it broke, now I just turn it around 180 halfway through cooking time.

Need to go get my GE Dual Wave, wood-grain trim, monster microwave out. It's from 85 I think. Had to do the same thing. Humongous too. Could probably rig it as a radar or something.

 

[William Gaatjes]

This EEVblog forum has some discussion about it HERE.

It includes photo(s) and datasheet(s), and some discussion about it.

That was a fun read.
Yaahooo. AC phase. But it is also the slack in the gearbox. and the 2 sets of stator poles have different sizes.

 

[Humpy]

I haven't seen such a strongly geeked out thread in a while.