We used microwaves that did not have rotating trays in the past, namely- flatbed microwaves. But a flatbed microwave could not heat the food evenly. So now, most of us have switched to turntable microwaves.
These microwaves have a rotating tray that ensures even heat distribution across the food. However, the microwave’s turntable can change the direction of its spin. Why does this change take place? Does it affect the food? We will talk about it briefly.
Why Does My Microwave’s Turntable Change direction?
The direction change occurs due to the cheap Synchronous AC motor. The motor has a magnetic coil where AC current is directly supplied. As the AC changes direction, the coil starts rotating in the direction of the AC at that time. So, based on the direction of the AC, your turntable can alternate rotating directions.
How Does A Microwave Turntable Work?
To understand the issue, first, we should understand how the turntable works in the first place. You can guess that a motor under the turntable rotates it. But this motor is a little different. The motor that runs the turntable is a Synchronous AC motor. This motor utilizes AC current directly.
The motor has a coil in the center. When the AC passes through the coil, it creates a magnetic field. There is another permanent magnet in the motor. That magnet interacts with the magnetic field.
So, when the polarity of the magnetic field shifts, the magnet starts rotating because of the attraction force. The initial movement energy boosts the mechanical parts to turn. The magnet is attached to a shaft that is connected with multiple gears. The gears reduce rotation speed and increase the torque of the turntable.
Why Do Microwave Trays Rotate?
Well, as mentioned before, the rotating tray has some pros. The microwave oven emits radio waves with ‘micro’ or small wavelengths. Wavelength is inversely proportional to frequency. So a small wavelength means high frequency. So the microwave oven emits high-frequency radio waves inside the cavity through an antenna.
High-frequency waves do not spread that much. In other words, high-frequency radio waves work as a flashlight beam or a laser light instead of spreading the waves like a bulb. So the microwaves hit only a portion of the food. So that portion gets overheated, and the other parts remain cold.
The rotating tray is used to prevent this problem. Rotating allows even distribution of heat throughout the food. So all the parts are evenly heated, and you can enjoy your apple pie.
Is A Microwave Turntable Necessary?
Turntables are not totally ‘necessary’ for microwaves. Microwave ovens that are made without turntables are called flatbed microwaves. They are still able to reheat food efficiently. But a flatbed prevents the even distribution of heat. So the food may contain hot and cold spots. So a turntable microwave does the job better.
However, you can still get the same effect in a flatbed by pausing the microwave after a few seconds and turning the container manually. Thus you can even promote cooking or heating without using the turntable.
Why Do Microwave Turntables Change Direction?
So now we have a fundamental understanding of how a microwave turntable works and why it is necessary. Now let’s move on to the next question. Why does the turntable change direction? The simple answer is AC current.
The key specialty of AC is that these current changes directions. The AC consists of the positive half cycle and the negative half cycle. In the positive half cycle, the current flows from the negative to the positive. At the negative half cycle, the direction is opposite.
The change in the AC cycle causes the polarity shift in the motor coil. This polarity shift facilitates the rotation of the motor. So, the direction is determined when the motor is started. For example, suppose the AC shifts from negative to positive half-cycle at the start. In that case, the turntable will move in one direction. But if the AC shifts from a positive half cycle to a negative, the turntable will rotate in the opposite direction.
Once the turntable has started rotating, it does not change direction. Because then the alternating cycles help rotate the tray. You can think of it as similar to a bicycle pedal. To keep the pedal spinning, you need to push and pull continuously. But the direction of rotation depends on whether you pulled or pushed at first!
So the direction of the rotation is random. However, because it depends on the cycle of the AC when the motor starts, some microwaves alternate the direction each time they start. They do it by adding ‘load.’
After starting, the motor will spin whichever way is the easiest to turn. Since the turntable was spinning one way before, it caused a load. So the motor spins back the other way because there is less load. So rotating the other way is easier.
Perks Of Changing Direction
There are a couple of advantages to changing directions. Firstly, the Synchronous AC motor is cheap. Some motors need a precise, fast & unidirectional start. So they use magnetic sensors that give absolute feedback on direction and speed.
Some motors must rotate the same way (e.g., disc drive motor). They may use sensor-less systems with a diode to force current flow in a single direction. But here, circuitry is needed to check rotation and adjust the powering if the direction is wrong. All of these methods increase the cost.
So the systems that do not care about direction and want the lowest cost use a sensor-less system and accept what comes. This is how the prices remain affordable for us.
There is another mechanical advantage. If the tray constantly rotated in the same direction, the same mechanical points would corrode and eventually wear out (The connected shafts and gears). This gives a reduced life to the machine. But on the other hand, spinning in both directions allows all the mechanical points and provides a prolonged life.
Also, when a motor is unidirectional, it can quickly get stuck or jammed. Unjamming a motor is not an easy task. If a jammed motor is forced to run, the motor can overheat and burn out. On the other hand, if a motor that can spin both ways gets jammed, it can easily un-jam itself by moving in the opposite direction.
Does Changing Direction Affect The Food?
A turntable is required for even cooking food in the microwave oven. So only the rotation matters here, the direction of rotation does not matter here. Experts also agree on this.
“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.
Why Does My Turntable Change Direction During The Cooking?
Usually, a microwave turntable will not change direction during the cooking process. However, if it does happen, this might denote some problems.
Firstly, if you put something heavy on the turntable, this might cause the load to increase. So the turntable might change direction to decrease the load.
The property of an AC motor is it changes its direction when it faces a resistance or ‘load.’ So anything that can artificially create the load can cause the direction to change when the microwave is running.
Lastly, if anything is stuck in the motor, the motor will try to un-jam it by constantly changing directions. So a stuck motor can also cause an alteration in spin direction.
What Is The Problem If My Microwave Turntable Changes Direction During Cooking?
Changing direction during cooking can be harmless in some cases. But the food can’t cook properly if the direction change occurs rapidly. So cold and hot regions may be seen in food.
Also, a change in direction during the cooking implies some problem in the system. So if the microwave is not repaired, it can stop working in the future.
How Do You Fix A Microwave Turntable That Won’t Spin?
- Please switch off the microwave and disconnect it from the socket for safety.
- Draw out the glass tray and the circular turntable guide. Clean them properly with hot water and soap to remove every residue. Thoroughly wash the rollers of the turntable guide and apply lubricant if necessary. Make sure the rollers spin freely.
- Scrub the internal cavity of the microwave oven. Make sure no leftover food residue is left.
- Make sure that the drive bushing is working. The drive bushing is a small plastic mechanism in the bottom of the microwave’s interior. Usually, a glass tray switches on the drive bushing in the microwave. Check closely if it is worn out or split in two. If the drive bushing is damaged, you will need to replace it.
- Reassemble everything back together.
- Now test your microwave again. Try with a mug of water to see if the problem is fixed.
Conclusion
Now you should have a brief idea about microwave turntables. This guide has been helpful to many people. You can share our content and follow our website if you think it was helpful too. For more content like this, subscribe to our newsletter.
