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What Is a Wax Motor?

By Lakshmi Sandhana
Updated May 17, 2024
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A wax motor is an inexpensive type of linear actuator device that is designed to push a plunger, causing it to move. It's also called a wax capsule and is used in many appliances where a short range of motion is required. Wax motors can be found in appliances like dishwashers and older models of washing machines. They were used earlier to lock the doors in washing machines before spin cycles were activated. Quite economical when compared to magnetic solenoids, wax motors are used to operate or pump thermal control valves and drive valves in heating mechanisms.

The three major components in a wax motor are a wax block, a plunger that bears on it, and a heat source that heats the wax. It operates in a very simple manner — an electric heater heats the wax block when it is activated. This causes the wax to heat up, which drives the plunger out. When the current is removed, the wax cools down and contracts, withdrawing the plunger in the process. Heating or cooling the wax, therefore, causes the plunger to be ejected or withdrawn.

Sometimes, countering springs are incorporated into the motor, or spring force is applied from external sources to push the plunger back into the housing. A wax motor requires almost no maintenance and offers many advantages over magnetic solenoids, which are used for the same purpose. Magnetic solenoids use a coil of wire to create a magnetic field.

This field is used to push the steel plunger out or pull it in. A wax motor is preferred over a magnetic solenoid in some cases because it has a much gentler and smoother operation. In comparison to a solenoid, it is slower to actuate and to return and, as a result, is less noisy in operation. Wax motors also use resistive loads, and those controlled with the help of triacs don't need snubber circuits.

It's also easy to check if they are functional by measuring the resistance; it's easy to spot a short or open circuit. As long as the resistance between the two terminals falls within a certain range, the device is functional. One of the greatest advantages this motor has over a solenoid is that it is less prone to failure. A wax motor survives in situations where the plunger is blocked and cannot travel all the way.

In contrast, a solenoid in the same situation may burn out. Solenoids are also expensive when compared to wax motors because they contain steel and copper wire. The motor also weighs less than a magnetic solenoid and is quieter; solenoids typically produce clicking noises. Speed is an advantage of solenoids, though, and they only need milliseconds for operation in contrast to wax motors. It may take more than half a minute for the plunger to fully push out in a wax motor.

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Discussion Comments
By anon1006786 — On May 21, 2022

Good article. I'm studying this wax motor recently. It seems like it's also called "thermoactuator". I'm considering to use it in my ventilation project.

Anyone know any manufacturers?

By anon989489 — On Mar 09, 2015

Very good article; informative.

I am investigating a wax motor incorporated into a piezo igniter on a gas stove cook top, but according to this article, it would be just too slow to repeatedly click a piezo igniter.

Is there such thing as a fast wax motor?

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