Introduction to Wax Motors: What are Wax Motors & How Do They Work?

What is a Wax Motor?

What comes to your mind about wax? Candles, crayons, car polishing? They're all correct but have you realized that you possibly have another wax usage around you inside your home appliances?

A wax motor is a little linear actuator designed for applications where a silent, strong, smooth motion is required to trigger a mechanical action. It converts thermal energy into mechanical energy by taking advantage of the unique volume expansion property of wax.

The structure of a wax motor is quite simple. It consists of a piston, a Positive Temperature Coefficient thermistor (PTC), and a sealed vessel filled with a fixed amount of solid wax. The piston is used to convert the force generated from wax volume expansion into a linear mechanical output force. The PTC is the heat source when energized to heat up the wax. The vessel is used to seal the wax during the transition between solid phase and liquid phase.

iSwell is manufacturing two types of wax motors as below. The left one is the core component of our Thermoactuator and the right one is the core component of our Electric Ball Valve Actuator.

We've published another blog post about Introduction to Thermoactuators. Click this link to read it.

How Much Does Wax Expand?

The volume of most materials expands when melting and shrinks when freezing. So does the wax. What makes the wax outstanding is that the volume expansion rate can be up to 20%. Almost no other material expands as much as wax. As wax can expand a lot more in volume than other materials, we can obtain a larger amount of linear motion with a fixed amount of wax.

Another good thing about wax is that it doesn't have a melting point outside the environment temperature range that we can not handle. We can even formulate the melting point of wax by different mixing ratios.

How Strong is Wax Expansion?

As a small amount of wax can expand so much when melting, the force generated from the expansion is enormous. However, this force is limited by the pressure tolerance capacity of the vessel and sealing materials. In our case, the output force of wax motor can reach 300N or more. This is quite enough for most applications. Furthermore, the output force is consistently high throughout the entire range of motion.

How Does a Wax Motor Work?

We've covered the basics of a wax motor above. It's time to explain how the wax motor works.

The PTC thermistor on the wax motor starts heating up when energized. And the wax inside the sealed vessel starts melting. As the volume-expanded wax takes up more space inside the vessel, it pushes the piston to move outward.

In return, when the PTC thermistor stops heating up, the wax inside the vessel cools down and contracts to the solid-state. The wax volume gradually shrinks. However, the piston will not return to its initial position itself. An external force, usually a spring, will be required to overcome the frictional resistance between the sealing material and the piston. With the assistance of the return spring, the piston goes back into the vessel.

Where is a Wax Motor Used?

You can find wax motors and thermoactuators in various applications, especially in the Home Appliance industry. For example:
•  Door Lock for laundry washing machines, dryers, dishwashers
•  Detergent Dispenser for dishwashers
•  Impeller Blower (Vent Fan Motor) for dishwashers
•  Exhaust Control for steam ovens
•  ...

You will also find various applications in the HVAC industry. For example:
•  Mixing Valves for hydraulic heating systems such as radiators, domestic heating systems to open, close, or adjust the water flow
•  Air Vent Fan to open or close louver
•  Freeze Protection Valve to avoid damage to pipes, solar systems
•  ...

Bottom Line

So, we've walked you through all the basic knowledges about wax motors. It's not as complicated as it sounds, right?

A wax motor is a little linear actuator utilizing the force generated from the wax solid-to-liquid phase transition. The operation of a wax motor is quiet, strong, and smooth.

The wax motor can be the simple but efficient solution to your project. And it still has great potential. Let's explore more applications together.

Useful External Resources

•  "Wax Motor" from Wikipedia
•  "Wax Motors" from CDN Inc.
•  "WAX MOTORS ~ A Full Understanding Of Operation & Construction" on Youtube