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Microwaves

Why Do Microwave Turntables Switch Directions? (Explained!)

Antonio Forde
Updated: June 7, 2022
4 min read

If you own a microwave, chances are you have observed its turntable switches directions after every cycle.

Why does it happen, and does it affect how the food heats?

Here’s Why Microwave Turntables Switch Directions:

Microwave turntables switching directions have to do with the type of motor used to turn the glass tray. Most microwaves have relatively cheap synchronous AC motors that can run in either clockwise or counter-clockwise direction, depending on where the motor is at the time the oven is turned on.

Do All Microwave Turntables Switch Directions?

turntable-switch-directions

Yes. Your appliance likely has a turntable that switches direction since most microwave oven manufacturers use less expensive turntable motors.

Utilizing cheaper motor types, such as synchronous motors, can save them a lot of money.

Turntables can turn in either direction when microwaves begin cooking. You may observe the tray rotating clockwise one time and counter-clockwise the next. This is normal.

The electrical circuitry in your microwave causes this change in direction.

When applied with alternating current (AC) power, cheap motors can run in random directions. Its design utilizes the shift in polarity to generate a magnetic field in a coil. 

This coil then interacts with a multi-poled permanent magnet.

The motor will turn one way at the start-up if supplied with a positive half cycle and turn the opposite way if equipped with a negative half cycle.

This is why microwave turntables can move in random directions when cooking or defrosting.

Once you turn on your appliance, the armature will rotate towards whichever pole the coil is nearest when it last stopped.

Unless there is a mechanical means to prevent it, the switch will happen randomly whenever you use your microwave.

More often than not, turntable motors rotate in the opposite way it was running before. 

This is primarily due to the energy-storage properties of the appliance’s gear train.

Some experts also explain that microwave turntables switch directions if you apply a more significant load than their output torque.

All motors need a starting force to go from zero rotation speed to target speed with or without a load attached. 

After a complete stop, the drive mechanism is usually pushed against the load in the last rotation’s direction.

When the motor encounters the load, it switches direction before picking speed, beginning the process again.

The system assembly needed to perform this is not as expensive compared with more robust motors and additional copper wires.

Motor direction is inconsequential in microwave applications, so using a pricey motor is impractical for manufacturers. 

The reverse in the direction happens only as an accidental byproduct of the motor supplied with AC.

So if your microwave’s turntable revolves in random, there is no need to worry. 

Your appliance is just behaving the way it should.

Does It Matter in What Direction Your Microwave Rotates When It Heats Food?

No. The direction your microwave turntable spins has no effect on the heating rate when cooking food.

It should not matter if it turns clockwise or counter-clockwise as long as it does turn.

Microwave ovens use microwaves for cooking and heating up food. These are types of radiation in the electromagnetic spectrum.

The magnetron or the vacuum tube inside the appliance produces the microwaves using power from the supply.

Once released from a metallic cavity called the waveguide, the waves bounce off the oven’s interior, passing through any type of container until they reach the food within.

Microwaves work on the principle of radiation, so when they penetrate the uncooked food, they heat up the molecules, causing them to vibrate.

Food with the highest liquid content heats up the quickest since liquid molecules are the easiest to warm through.

To distribute the waves evenly throughout the oven, you need to control the movement of the food. This is the purpose of the turntable.

Rotating the turntable is necessary to ensure that the food item gets the same amount of heat from all angles.

This ensures that microwaves spread evenly and that your meal cooks simultaneously and uniformly. I have explained why microwaves rotate the food more-in depth here.

The direction the turntable turns is not essential. The food gets properly cooked either way, whether it turns left to right or vice versa.

If you have a faulty turntable, you will notice that certain parts of your meal are not heated enough. Reasons, why a turntable might break, are listed here.

When a wave is trapped in the cavity of your oven, there is bound to be interference. 

Waves that interfere constructively result in increased energy, creating hot spots that heat up the food items near them.

Those that interfere destructively lead to no net radiation. This generates cold spots. Food at these spots tends to remain cold.

This uneven distribution of heat can be solved by spinning the turntable. 

Other ovens are equipped with stirrers as a substitute for turntables. This feature magnetically mixes the food to spread heat evenly throughout the food container.

Some units contain rotating reflectors as an alternative for turntables. These are located just below the magnetron of your appliance.

Rotating reflectors function just the same as regular turntables. They are designed to distribute microwaves evenly and efficiently.

For those older models of microwave ovens that do not contain rotating trays, manually stirring the food is needed to avoid cold spots.

Even without stirring, the food will still get cooked, perhaps just not as thoroughly as you expect it to be.

Sources:

The New York Times

Scientific American

Science ABC

Written by
Antonio Forde
I'm the head-writer @ Ask The Home Geek (or, in plain English, I'm the guy writing & editing the majority of the content here). Current learning project: Korean.
Have any questions? Write us a message.
Antonio Forde
I'm the head-writer @ Ask The Home Geek (or, in plain English, I'm the guy writing & editing the majority of the content here). Current learning project: Korean.