Electronic or variable fan speed controllers offer continuously variable speed control for AC fans. They use phase angle control, Triac technology, to reduce the motor voltage. The lower the motor voltage, the lower the fan speed.
TRIAC speed controllers
Electronic speed controllers are also referred to as variable speed controllers or TRIAC speed controllers. They regulate the speed of AC motors continuously variable by reducing the motor voltage without steps. Electronic speed controllers operate completely silently and require no configuration before use. They are typically used to regulate fan speed. Most customers are willing to accept the disadvantage of a slightly lower energy efficiency (compared to frequency inverters) because the advantage of user-friendliness and easy commissioning is more important to them.
Completely silent fan speed controller
Electronic fan speed controller use electronic components to reduce the motor voltage and to regulate motor speed. For this reason, they operate completely silently unlike transformer fan speed controllers. The electronic components do not generate any sounds unlike an electrical transformer (which generates a soft humming sound, caused by the electrical transformer). Electronic speed controllers can therefore be used in applications where the noise of a transformer speed controller would be perceived as disturbing.
Motor noises at low speed
The motor speed is regulated by reducing the motor voltage. This is realised by blocking parts of the supplied voltage. In technical terms this technique is called ‘Phase Angle Control’. Phase angle control technology causes that the motor voltage no longer has a perfectly sinusoidal shape, since there are pieces missing. Certainly at low speed the motor voltage will therefore be less sinusoidal. This non-sinusoidal motor voltage makes the motor noisier. Depending on the motor brand, these motor noises can be more pronounced. In most cases, it will be more noticeable at low speed.
With a transformer speed controller, the controller itself will produce a humming sound, but the motor will operate quietly. With an electronic speed controller, it is the other way around. Here, the motor makes more noise, while the controller is quiet.
Continuously variable speed control
Electronic speed controllers regulate fan speed by reducing the motor voltage continuously variable (without steps). Transformer fan speed controllers also regulate the motor speed by reducing the motor voltage. The difference is that transformer fan speed controller do this in steps, while electronic fan speed controllers do this continuously. Both types of speed controllers are suitable for voltage-controllable motors. These are electric motors where the speed can be controlled by lowering the motor voltage while the frequency remains constant. Most fans with AC motor can be controlled in this way. Both TRIAC and transformer fan speed controllers can be used in applications where the torque decreases with speed, such as fan speed control.
Phase Angle Control regulates motor speed
Electronic fan speed controllers use electronic components to control motor speed. The most important one is the TRIAC or TRiode for Alternating Current. A TRIAC is visualised in the image at the right side. It is the black electronic component with the three pins. Electronic fan speed controllers are also referred to as TRIAC controllers. A TRIAC is a three-electrode semiconductor that can be seen as a switch. Either it allows the electric current to pass or either it blocks the flow of electric current.
The more precisely the TRIACs are controlled, the less noticeable the additional motor noise will be. For this reason, the latest Sentera electronic fan speed controllers are all equipped with advanced microprocessors. This makes it possible to reduce additional motor noise to an absolute minimum. Cheaper variants of electronic fan speed controllers usually control the TRIACs with much lower accuracy. This results in additional motor noises and faster wear of the electric motor.
Typically, TRIACs can switch electric currents with a maximum current of up to 10 A. For this reason, this type of controller is usually only available for single-phase motors.
TRIAC controllers require a minimum load
A TRIAC has the special property that it needs a minimum load before it can function. If no load (a motor, a light bulb, …) is connected to the speed controller, it will not function. Only when a minimum electrical current can flow (typically 10% of the maximum current), the electronic speed controller will function normally. So if you want to verify whether the speed controller is functioning correctly, a load must be connected! Without this load, it appears as if the speed controller is defective because the TRIACs cannot conduct. This is not the case with a transformer speed controller. Transformer speed controllers do work without a load.
User-friendly and easy commissioning
The electronic circuit that controls the TRIACs, makes it possible to offer additional setting options. These additional setting options are usually not available on less advanced transformer speed controllers. For example, most TRIAC controllers allow the minimum or maximum speed to be changed according to the needs of the application. Since fans are usually oversized, it is important in many applications to adjust the maximum speed. Thanks to these additional setting possibilities, this type of controller can be better optimized for the application than transformer fan speed controllers. Some TRIAC speed controllers are deliberately kept simple to keep the price down, other series offer more setting options. There are two ways to adjust settings on Sentera electronic speed controllers: via Modbus RTU communication (software) or via a trimmer (small potentiometer, mounted on the printed circuit board).
In most Sentera products, settings can be changed via software, by adjusting a value in a Modbus holding register. A Modbus network consists of a master device and at least one slave device. The master device can be a PC with configuration software, the slave device can be the speed controller. The Modbus master device can change certain values in the slave device and read out other values. This makes it possible, for example, to change the minimum speed by adjusting the value of the corresponding Modbus Holding register.
Another example: in some electronic fan speed controllers the operation method is adjustable. This makes it possible to change the behaviour of the fan speed controller by writing a different value in the corresponding Modbus Holding register. By default, the operation mode is ‘from low to high (value 1)’, but it can be changed into ‘from high to low' by adjusting the value of the Holding register towards 2. If the fan speed controller is connected to the SenteraWeb cloud, it is even possible to read out or to adjust the values of the Modbus Holding registers remotely. This can only be done by the configurator of the installation.
Some basic Sentera TRIAC speed controllers do not feature Modbus communication to keep the price down. In these devices it is usually possible to adjust the minimum or maximum speed via a trimmer, mounted on the printed circuit board.
Frequency inverter versus electronic fan speed controller
What is the difference between a frequency inverter and an electronic speed controller? In short, a TRIAC controller is cheaper and easier to use, while a frequency inverter will control the electric motor in a more energy-efficient way, especially at low speed.
But what are the real differences? This is not so easy to explain in a non-technical way. Here is an attempt: A TRIAC speed controller regulates the motor speed by reducing the amount of incoming power before sending it to the motor (reducing the motor voltage). On the other hand, a frequency inverter not only reduces the power but also changes how fast the power cycles (it also changes the frequency of the motor voltage). By adjusting both the frequency and the voltage, the motor torque can be controlled in addition to the motor speed. Motor torque means the force of the electric motor. So the frequency inverter can control both how fast the motor rotates and how strong it is. By optimizing motor speed and torque, energy can be saved at lower speeds.
Explaining the difference between a Frequency inverter and TRIAC speed controller in a more technical way would sound like this: A frequency inverter does not only reduce the motor voltage, but it also changes the frequency of the motor voltage. This makes it possible to keep the ratio between motor voltage (V) and frequency (f) constant. This control algorithm is also referred to as constant V/f control.
If the motor voltage is reduced without adjusting the frequency - this is what a TRIAC speed controller does - the magnetic flux decreases. Since motor torque is directly related to the magnetic flux in the motor, this leads to a reduction in motor torque at lower speed. The motor may struggle to drive the load, especially at lower speeds, and could even stall under heavy load conditions. This problem will not occur in applications requiring low starting torque. Since a fan usually requires a relatively low starting torque, this type of applications can usually be controlled by a TRIAC speed controller.
There are also applications that require a high starting torque. For example, hoisting applications require maximum motor torque from minimum speeds. As soon as the mechanical brake is released, the electric motor must immediately deliver full torque to keep the load under control. For such applications, a frequency controller is required. A TRIAC speed controller is not sufficient here.
With the TRIAC speed controllers we aim at applications in the HVAC industry, such as controlling fans or centrifugal pumps. Most fans follow a quadratic torque curve. This means that the required motor torque increases quadratically as the speed increases. At low speeds it is easy to get the fan running. As fan speed increases, more motor torque is needed to further accelerate the fan. This increase in required motor torque is not linear but quadratic. For this reason, a lot of energy can be saved by reducing fan speed if possible.
Optimizing the magnetic flux is the reason why a frequency inverter can control the motor in a more energy-efficient way. Reducing the motor voltage while keeping the frequency constant causes the motor to draw more electrical current at low speed to compensate for the reduced magnetic flux. This increased current leads to higher losses in the motor windings, resulting in excessive heat. Keeping the V/f ratio constant ensures that the motor operates more energy efficiently, with optimal current levels. The motor produces sufficient torque without drawing excessive current, which minimizes heat generation and avoids overheating.
Why TRIAC speed controllers remain interesting
Sentera TRIAC speed controllers are still widely used to regulate fan speed. Their ease of use, simple construction and attractive price are the main advantages. The fan speed can be adjusted continuously variable (without steps). The fan speed controller operates completely silently. Disadvantages of this technology are the lower energy efficiency compared to frequency inverters and the possibility of motor noises at low speed. Sentera TRIAC speed controllers are designed to minimise these disadvantages as much as possible. Due to the very accurate control of the TRIACs using microcontrollers, the motor noises are in most cases hardly noticeable.
Product range of Sentera TRIAC fan speed controllers
Sentera is one of the leading manufacturers of fan speed controllers. For two decades, our electronic fan speed controllers have been the standard in the HVAC world. Quality and user-friendliness has always been our top priority. Due to the great success, many variants were created. As a result, it is not always easy to get an overview of this product range. The most important properties of the different series are briefly summarized below.
Sentera electronic fan speed controllers are available with a maximum current rating of 10 A. They feature a high-quality plastic enclosure. The versions with higher current ratings are equipped with a metal cooling fin for heat dissipation. The enclosure is manufactured in our own Sentera plastics factory from flame-retardant ABS plastic. The cooling fin guarantees sufficient heat dissipation and is calculated for the maximum power of the controller.
A first group contains electronic fan speed controllers with build-in control switch on the front panel. They control single-phase voltage controllable motors with a maximum current of 10 A. These speed controllers in particular are easy to install and operate. Motor speed can be adjusted via the controls on the front panel.
- For residential applications, we recommend the SDX and SDY series. They control single phase motors with a maximum current of 3 A. Both versions are easy to install on a wall or flat surface or in a standard European wall-socket. The minimum speed can be adjusted via an internal trimmer.
SDX-1-x5-DM series offer more flexibility thanks to the Modbus RTU communication. Via the Modbus holding registers, additional settings can be made. This makes it possible for example to inverse the operation from 'high to low' speed into 'low to high' speed. - For logistics or industrial applications we recommend the ITR-9 series. They control single phase motors with a maximum current of 10 A. The minimum motor speed can be adjusted via an internal trimmer on the PCB. The integrated ON-OFF switch is placed at the side of the enclosure. If necessary, this ON-OFF switch can be disabled. The enclosure is designed for surface mounting and offers an IP54 protection degree against ingress of dust and humidity.
The similar ITRS9 series look almost identical, but they feature two extra inputs for remote start-stop commands, one extra output for alarm notifications and the possibility to connect the motor thermal contacts (temperature sensor integrated in the motor windings to detect motor overheating).
A second group offers electronic fan speed controllers with analogue input. These versions do not have integrated control switches. They require an analogue signal to set the desired fan speed.
Sentera also offers demand based electronic speed controllers. They regulate fan speed based on the ambient temperature.