The minimum speed or low speed is different for each AC fan. Therefore it is important to adjust this level according to the installed fan. The minimum speed level or minimum motor voltage can be adjusted via a trimmer. Some series also have Modbus RTU communication. In this case, the settings can be adjusted via Modbus RTU communication. During operation, asynchronous motors heat up due to electric currents flowing through
the motor windings. The air flow generated by the motor compensates this heating process. If the motor speed is not high enough, the excessive heat might cause melting of the isolation of the motor windings and damage the motor.
In some extreme cases, a low motor voltage might even cause stalling of the motor: electric currents are flowing through the motor windings while the motor is at standstill (stalled or blocked). To avoid this, the minimum motor
speed should be set high enough to avoid excessive heating or stalling of the motor. The minimum required motor voltage depends on the type and brand of the motor.
In case the fan is overdimensioned, it can be useful to reduce the maximum motor speed. Reducing the high speed level in accordance with the installed ventilation system increases the comfort and
realises energy savings.
There are different ways to accelerate a motor. We distinguish between Kick start and Soft start. The choice between these two acceleration methods depends on your application. Applications with
high inertia might need a higher torque at start up to avoid stalling of the motor.
Kick start — the motor will accelerate immediately from standstill towards maximum speed. The full motor torque is almost immediately available. After this start-up period (typically 8 – 10 s), the motor will decelerate
towards the requested fan speed setpoint. This starting method is often used to avoid motor stalling at low speed. The disadvantage is the mechanical stress at start-up and a high motor start current.
Soft start — the motor will smoothly accelerate from standstill towards the requested fan speed setpoint. This starting method gives you the advantage of reduced mechanical stress and lower motor starting currents.
Due to the reduced motor torque during start up, this acceleration method is not ideal for high inertia applications.
Most Sentera fan speed controllers have an unregulated output. The unregulated output (230 VAC) is activated during motor operation. Typically, the unregulated output is used to power an external 'motor
run indicator light' or to supply the start-up capacitor (in case of single-phase motors with external start up capacitor).
Sentera fan speed controllers are manufactured in Europe. We use electronic components of the highest quality. Sentera fan speed controllers should not be overdimensioned. A Sentera fan speed controller
with a maximum current of 5 A is designed to control a 5 A motor on a continuous basis.
Thermal motor protection
The low speed level is not only adjustable to minimise motor noise at low speed. Operating a motor during a longer period at low speed is not without risks. Next to the increased motor noise, there is the risk
of overheating. At low speed, the motor is cooled less. Motor overheating causes degradation of the insulation of the motor windings. This can lead to short circuits, and eventually motor
failure. To reduce the risk of overheating, we recommend not to set the minimum motor voltage too low. The minimum motor voltage limit is different for each motor type.
Some AC motors are equipped with thermal contacts – often called TK contacts. These thermal contacts measure the temperature in the motor windings. In case of
motor overheating, the TK contacts are opened. Some fan speed controllers provide extra protection against overheating via their TK monitoring function (only applicable for motors with TK contacts). This functionality
the motor in case of overheating. At the same time, the alarm output will be enabled to indicate a motor problem. In case your motor is not equipped with TK contacts, don’t forget to bridge the
TK terminals of the fan speed controller or to deactivate the TK monitoring function.
Electronic or variable fan speed controllers provide infinitely variable speed control for single-phase or three-phase motors. Typically, they are used to control AC fans or pumps in HVAC applications.
They use phase angle control - TRIAC technology - to adjust the motor voltage and to control fan speed. Thanks to this technology, these fan speed controllers are completely silent. This means that the mains voltage is reduced
by cutting pieces out of it. The remaining motor voltage will not have a perfect sinusoidal shape. Most of our
fan speed controllers are microprocessor controlled. That makes it possible
to optimise the zero-cross detection. This results in an exceptionally quiet motor operation. Nevertheless, depending on the motor type some additional motor noise at low speed might occur due to the non-sinusoidal shape of the
motor voltage. Increasing the minimum motor voltage will reduce the noise level.
Electronic fan speed controller
Electronic fan speed controllers provide infinitely variable
speed control for AC fans. Just like frequency inverters… So what is the difference? A frequency inverter uses Pulse Width Modulation – IGBT technology – to adjust the motor voltage and frequency. This offers a sinusoidal motor voltage in all circumstances and more precise motor control. However, due to the higher switching frequency
of the IGBTs, special filters are required to reduce the EMC pollution in the power grid. This extra hardware has a cost. Precise motor control also means: more complex to configure.
How to control AC fan speed? There are many possibilities to adjust AC fan speed. The simplest way is to use a fan speed controller with integrated potentiometer. We call this product group ‘manual motor control’. The motor speed can be adjusted manually via the potentiometer on the fan speed controller. Some versions have a
potentiometer with integrated on-off knob. Other models have a separate illuminated on-off knob on the side of the enclosure.
These fan speed controllers are available in different enclosure types. Surface mounting, inset mounting or DIN rail mounting are possible. Click on the product images and discover all products:
Remote manual fan speed control
In some applications, the control unit (potentiometer) is installed separately from the fan speed controller. The fan speed can be adjusted manually via the
The potentiometer transmits the requested fan speed to the fan speed controller. The fan speed controller adjusts the motor voltage and the fan speed. There are two ways to transmit the requested fan speed: via
0-10V control signal or
Modbus RTU communication.
Analogue control signals have been popular in the (home) automation industry
for many years. Even today, many fan speed controllers or frequency inverters are controlled via a 0-10 V signal. It is a simple technology that works fine if cable lengths remain limited. If the control lines are
installed nearby power lines, there is a risk of interferences. We advise to keep the cable length of the analogue control signal limited to maximum 10 m. In case longer cable lengths are required, it is preferable
to transmit the requested fan speed via Modbus RTU communication.
To control a device via
Modbus RTU communications has many benefits compared to an analogue control signal.
Modbus RTU is a serial communication platform that uses RS485 technology. This technology makes it
possible to transmit information over larger distances. Cable lengths up to 1.000 m are possible. The risk of disturbances is minimal.
Solutions for remote variable fan speed control are available with different enclosures for surface mounting or DIN rail mounting are possible. Click on the product images and discover all produtcs:
Demand based fan speed control
In this case, fan speed is controlled automatically in function of demand. Fresh air supply is essential to create a healthy environment with good air quality. Since most people spend the majority of their time inside,
indoor air quality matters. Temperature,
relative humidity, CO2 and TVOC are the most important parameters that determine an occupant's comfort and productivity. Sufficient fresh air supply
reduces the risk of COVID-19 transmission via aerosols. That’s why automatic or demand based fan speed control is the best choice for most ventilation systems. Fan speed is always optimised to meet
the local circumstances. This control solution provides the best balance between a healthy indoor air quality and energy efficiency.
The optimal fan speed is calculated by
HVAC controllers or directly by the
intelligent HVAC sensors. Fan speed can be
optimised in function of temperature, relative humidity, CO2 level, air quality, CO level, differential pressure or a combination of these. Some sensors also have an ambient light sensor. This makes it
possible to distinguish between day-night regimes. Discover all possible combination on the
solution page of our website.