Introduction to Thermoactuators: What are Thermoactuators & How Do They Work?

In this article, we will provide you with a comprehensive overview of thermoactuators, covering all the essential information you need to know. Whether you're exploring potential solutions or seeking a deeper understanding, we've got you covered. Let's dive right in!

What is a Thermoactuator?

A Thermoactuator is small linear actuator with a wax motor inside. It produces silent, strong, and smooth motion by utilizing the unique wax volume expansion characteristic through its plunger. It's widely used in Home Appliance and HVAC Industries to trigger the open or close actions of mechanical parts such as door locks.

As you can see from the image above, the structure of a thermoactuator is very simple and compact. It consists of a wax motor, flame-retardant plastic housing, a plastic plunger, a return spring, and tab terminals.

The wax motor is the core component of a thermoactuator to convert thermal energy into mechanical energy. We posted another introduction blog for wax motors. We recommend you read it before continuing to this post. The plunger delivers the linear movement as wax expands. The return spring helps the plunger and piston move back to their initial position when the wax solidifies. The plugs are used to connect electricity to the PTC thermistor. All these components are assembled within the plastic housing.

Why We Need a Thermoactuator When We Already Have a Wax Motor?

We've mentioned in this blog post that the wax motor requires an external return spring to have the piston go back into the sealed vessel as the wax solidifies. And the PTC thermistor needs to be energized in order to heat up the wax inside the wax motor. Besides, the insulation is a must to ensure safety.

So here comes the thermoactuator.

How Does a Thermoactuator Work?

The thermoactuator does the same thing as a wax motor. It convert the energy generated from the solid-to-liquid volume expansion of wax into mechanical force. Read this blog post about how a wax motor works.

The PTC thermistor starts heating up the wax inside the wax motor when we power it on. Then the wax melts into liquid state and takes more space in the wax motor. The piston is forced to move outwards and pushes the plastic plunger outwards.

When we disconnect the power supply to the thermoactuator, the wax cools down and contracts to solid state. The wax volume shrinks. With the assistance of the return spring, the piston and plunger move back to their initial position.

How Strong is a Thermoactuator?

As a small amount of wax can expand so much, the force generated from the phase transition is enormous.

Let's take our thermoactuator P21.8T as an example. Actually, the output force is limited by the pressure tolerance capacity of the plastic plunger. However, the output force still can reach more than 300N in our Limit Test.

In the Limit Test, we placed a dynamometer with a stroke ruler on the top of the plastic plunger. Then we recorded the values of the output force when we forcibly restrict the plunger at different strokes.

This thermoactuator P21.8T still worked well after a 10-minute operation at the limit stroke of 0mm, except there was a deep dent (approximately 2mm depth) left inside the plunger caused by the piston and high force.

As you see from the graph in our Limit Test, the shorter the working stroke, the bigger the force. And through mechanical conversion calculations, it has been determined that when a 100N load is applied to the piston of the wax motor, the working pressure in the wax motor reaches nearly 500 bar.

This Limit Test showed us how strong a thermoactuator is. 300N is quite enough for most applications. But we should be aware that excessive force can cause irreparable damage to the plastic plunger and adversely shortens the effective stroke and lifetime of thermoactuators.

Check this post about how we test our thermoactuators to ensure zero defects.

How to Select Appropriate Thermoactuators?

We listed basic models in our Thermoactuator Product Page. But you need to consider different aspects when you're selecting a thermoactuator.

1. The Working Direction

The plunger can work in PUSH or PULL direction. The "T" in the model name stands for PUSH direction and "L" stands for PULL direction. PUSH means the plunger goes out from the housing and PULL means the plunger goes into the housing. You need to consider which direction is required to trigger the mechanical action in your application.

2. The Working Stroke

The working strokes of plungers are available in 6mm, 8mm, and 12mm. The number "6", "8", and "12" in the model name stand for the rated working strokes. Even if there's nothing to PUSH or PULL for the plunger, the plunger won't go beyond the tolerance of rated strokes because there is a limitation structure inside the housing.

Another thing needs to be considered is the actual working stroke in the application. The Limit Test we explained above tells us that the effective working stroke will be shortened if we limit the working stroke too short. We don't recommend limiting the working stroke lower than 4.5mm for 6mm models,  6.5mm for 8mm models, and 9mm for 12mm models.

3. The Working Voltage

The thermoactuators are available in 110-240V, 24V, and 12V. The difference is only the PTC thermistor. We apply the same PTC thermistor for 240V and 110V. To change a thermoactuator of 110-240V version to 24V version, all we need to do is to replace the PTC thermistor.

4. How Quickly for The Plunger to Start Working

There are also Normal and Fast versions for thermoactuators. The plunger of a Fast thermoactuator starts moving earlier than a Normal thermoactuator. However, for each time, our Fast thermoactuator can not be energized for more than 5 minutes while the Normal thermoactuator can.

This is because our Fast version thermoactuators uses a PTC thermistor with higher temperature. It starts working earlier because the PTC heats up speed is faster. This will results in a higher surface temperature which is not good for the plastic housing. That's why there is a 5-minutes energization time limitation for our Fast version thermoactuators.

So if you want to complete a mechanical action more quickly and decide to use the Fast version thermoactuator, please make sure to de-energize it in 5 minutes.

5. The Wax Melting Temperature Range

Every thermoactuator contains a fixed amount of wax. But using the same wax melting temperature range for all kinds of applications is not a good choice sometimes. Let's take two thermoactuator applications as examples. One is the dishwasher detergent dispenser and the other is the extractor fan.

The dishwasher works under a much higher temperature, while the extractor fan works under the ambient temperature. Using the wax with a lower melting temperature range for the extractor fan means we can use a PTC thermistor with lower temperature. As a result, the power consumption will be lower, the plunger will start moving more quickly, and the working temperature of the thermoactuator will be more friendly to the plastic housing. Furthermore, it will also extend the product service life.

The dishwashers prefer wax with a higher melting temperature range. It's because the working temperature of a dishwasher is much higher than the extractor fan. If you use the wax with a low melting temperature range, the thermoactuator will start working when you don't expect it to. For example, the detergent dispenser opens to release the detergent before the dishwasher reaches the set working temperature.

6. The Installation Condition

If the space is limited or screw installation holes are not necessary in your application, we can offer our thermoactuators with one or no screw-installing holes. There are no cut marks on the plastic housing.

Furthermore, if there is a requirement for dust-proof in the application, we can offer the thermoactuators with no vents on the plastic housing.

External Factors That Affect the Plunger Initiation Speed

After power is supplied to the thermoactuator, the plunger will only start moving once the wax undergoes a phase transition from solid to liquid. Therefore, there is a response time as the wax absorbs heat. But some external conditions can affect the plunger initiation speed.

1. The Working Load

As indicated in the Limit Test section of this post, the thermoactuator demonstrates a high force output capability. Conversely, when the load on the plunger is smaller, the pressure inside the wax motor decreases, resulting in faster plunger initiation.

During our tests on the P21.8T thermoactuator at room temperature, we observed a time difference for the plunger initiation of up to 20 seconds between a working load of 10N and 70N.

2. The Ambient Temperature

The wax melting principle decides that as the ambient temperature increases, the time needed for wax melting decreases, resulting in a faster initiation of plunger movement.

During our tests on the P21.8T thermoactuator under a 70N load, we observed a time difference for the plunger initiation of up to 20 seconds between an ambient temperature of 20°C and 80°C.

The Benefits of Thermoactuators

After exploring the details of a thermoactuator, it is important to understand its benefits, particularly when compared to a solenoid:

Consistent Force
Thermoactuators provide a consistent high thrust throughout their entire range of motion, ensuring reliable actuation.
Smooth and Silent Operation
Thermoactuators offer smooth and silent plunger operation, minimizing noise and vibration during use.
Durability and Reliability
Thermoactuators are known for their outstanding durability and reliability as it's a component closer to mechanical, making them suitable for long-term use.
Compact Size and Structure
Thermoactuators feature a compact product size and simple structure, allowing for easy integration into various systems and devices.
Electrical Protection Not Required
Unlike solenoids, thermoactuators do not require additional electrical protection, simplifying installation and reducing overall costs.
Electromagnetic Interference-Free
Thermoactuators do not produce electromagnetic interference, ensuring reliable operation in sensitive electronic environments.

Where Can Thermoactuators Be Used?

Thermoactuators have been widely used in the home appliances and HVAC sectors, including automatic exhaust devices for steam ovens, automatic door opening mechanisms for dishwashers, detergent dispensers for dishwashers, safety door locks for home appliances, and automatic control for extractor fan louvers.

If your applications demand strong, smooth, and silent linear actuation, and response time is not a critical factor, thermoactuators are the perfect solution for you. Their exceptional performance and reliability make them an ideal choice.

Bottom Line

In summary, thermoactuators are highly reliable and durable component used in various industries, including home appliances and HVAC sectors. They operate by leveraging the wax phase transition, delivering quiet, smooth, and linear actuation, making them an ideal solution for applications requiring strong force. Compared to solenoids, thermoactuators offer consistent force throughout their range of motion and outstanding durability and reliability.

Useful External Resources

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