13.05.2024 | reading time approx. 5 min.


Why EC motors are the best choice for fans

The European fan market is undergoing a significant change: while the sales figures for fans with AC motors are stagnating, EC motors are recording a steady increase. This is mainly due to the ErP requirements, which stipulate a minimum efficiency for the overall ‘fan’ component.

Conventional AC external rotor motors typically achieve a maximum efficiency of around 85%. In contrast, external rotor motors in the ZIEHL-ABEGG ECblue series achieve efficiencies of up to 93%. In order to fulfil the increasingly stringent ErP requirements, highly efficient motors are essential, even if the impeller is already efficient. This is where EC motors come into their own.

Read more about the efficiency of electric motors here.

How are these impressive differences in efficiency achieved?

The way the motors work plays a decisive role here.

In an AC motor, the current in the motor windings creates a magnetic field that induces a current in the rotor’s short-circuit cage. The current generates a magnetic field that lags behind that of the stator windings. The difference in speed creates a torque that drives the rotor.

EC motors also generate a magnetic field in the motor windings, but this attracts the permanent magnets in the rotor without the need for an additional magnetic field.

The difference in efficiency is due to the different way the motors work. With AC motors, a lot of energy is required to build up the magnetic field in the rotor, whereas with EC motors, this energy is already used during production and is no longer required during operation. The control also differs between the motor types: EC motors are typically controlled analogue (e.g. via a 0-10V signal) or digitally (e.g. via Modbus or other protocols). The speed can be flexibly adjusted and the components can be monitored and optimised by a higher-level control system. In the case of the more simply designed AC motors, the control depends on the control component connected upstream of the motor.

Challenges can arise when the motors are used in critical applications where harmonics can cause difficulties.
In large EC motors, these harmonics occur in the intermediate circuit due to the conversion of alternating voltage into direct voltage. The smoothing of the voltage by capacitors leads to the unwanted harmonics that can negatively affect the grid. To solve this problem, filtering is required. This can be done either directly in the engine through a built-in active filter or downstream through an external filter.

Despite this disadvantage, EC motors offer advantages that cannot be achieved with AC motors.

The integrated sensors make EC motors ‘smart’ and can actively influence processes, for example by recording and storing temperatures, vibrations, speeds, run-ups or anomalies and visualising them via cloud services. This enables well-founded statements to be made about the operating status of the system, allowing appropriate measures to be initiated. The requirements of the ErP Directive offer an opportunity to rethink systems and increasingly rely on EC fans. Although modern EC motors generate harmonics, these can be contained through the use of filters, while at the same time offering a wide range of functions and maximising efficiency.