20. May 2020

Detect interfering electromagnetic fields

All electrical devices inevitably generate electromagnetic fields during operation. You can observe this very well in everyday life. An example is the flickering of the old PC monitor when a call comes in on a nearby cell phone. The cause of this disturbance is the electromagnetic field of the phone. Electromagnetic radiation is also generated by the motor in e-mountain bikes, as it generates its drive force with the help of such fields between the rotor and stator. The power electronics can also cause such effects. This includes switches, regulators and converters of electrical voltages. Likewise, such fields are created around all cables through which current flows in the e-mountain bike. The longer such cables are, the more such effects are amplified. If such disturbances in the e-bike affect the control system and the motor unintentionally changes its behavior, dangerous situations can arise, for example in road traffic. Therefore, when designing an e-mountain bike, engineers must ensure that the bike does not interfere with the function of other electronic devices. Conversely, it is necessary to shield the electronic components of an e-bike from interfering fields on their part.

Testing of electromagnetic fields according to DIN standard

For ROTWILD, this means that the company must not only test the motor as an electric drive for its radiation and its protection against interference from electromagnetic fields. All other components such as the lighting, the battery and the display must also meet the standards, both individually and as a complete system on the roadworthy E-MTB. The DIN EN 15194:17 guideline defines the corresponding requirements for testing and electromagnetic compatibility. This test is divided into three parts. In the immunity test, engineers aim antennas at the bike that emit interference in the frequency range from 20 to 2000 MHz. On the test bench, the testers switch on the engine at a realistic speed of 22.5 km/h. During the test, the change in speed must not exceed 10%, and the operating state of the system must also remain unchanged. All measurements take place both at the front and rear of the wheel, as well as additionally in standby and push-assist mode. During the test, the test bench logs the output power of the drive and its speed. During this process, the change in speed must not exceed 10% and the operating state of the system must also remain unchanged. In addition, cameras are installed in the measuring room. These monitor the condition and behavior of lighting systems and the control unit.

Preparations of the test stand in the laboratory of Hansecontrol Zertifizierungsgesellschaft mbH, here with the ROTWILD R.T750 TOUR.

"The most important point is that in the end we have to shield in the product all current-carrying components and of course all cables. In combination with careful assembly, we can rule out irregularities and interference in our ROTWILD bikes." (Testimonial David Dönigus)

The EMC test includes extensive test procedures

The focus is also on the electromagnetic fields emitted by the e-bike. In the field of interference emission, the engineers check whether this is within certain limits. For this purpose, the bike runs on the test bench with a realistic load of 75% of the rated continuous power. The antennas in the test lab, which are precisely aligned with the bike, detect possible emissions in a frequency range from 30 to 1000 MHz. Outside this bandwidth, emissions can interfere with radio frequencies, radio equipment or machinery, for example. The testers take measurements on both sides of the bike and in standby mode. The ESD test checks whether potential differences in the environment interfere with the e-bike's electronic components. In practice, the rider can cause these himself. Anyone can become electrostatically charged. If you then touch the e-bike's display, for example, the voltage can discharge. In the test lab, this is done with the help of ESD guns, which discharge contact discharges at +/- four kV and air discharges at +/- eight kV specifically onto the e-bike. The bombardment must not cause sustained changes in the operating state of the entire bike and all electronic parts.

"We have to perform the tests very accurately. Setting up for the measurements represents a considerable effort. The highest precision is required when adjusting the test stand and aligning the measuring antennas." (Testimonial David Dönigus)

EMC tests in cooperation with specialized experts

ROTWILD commissions renowned testing institutes, such as Hansecontrol Zertifizierungsgesellschaft in Hamburg, for the complex EMC tests. They have the necessary high-quality measurement equipment and a test stand with mobile cameras. The entire test setup is located in an absorbent measuring hall, where atmospheric pressure, temperature and humidity are optimally matched. The pace of new developments is enormous, especially for e-bikes. Since all new components must be tested in accordance with DIN guidelines, the time-intensive tests are subject to a tightly timed process. As an absolutely necessary procedure, they therefore have a very high priority in the complete development of a new bike - from the first draft to series production. Since ROTWILD tests all components in combination, the main focus is on the cable layout, cable routing and their shielding. This is because effects from sources of interference can be amplified via the cable run. In addition, the general conditions for flawless EMC tests are a challenge, especially for displays. Pushbuttons must be sealed in the best possible way in order to comply with the required limit values. In addition, these components often have housings made of plastics that shield electromagnetic fields to varying degrees depending on the composition of the material. However, with a clean product design, even these products can be manufactured in such a way that they pass all electromagnetic compatibility tests.

David Dönigus

David Dönigus has been on board at ROTWILD since 2014. After studying mechanical engineering and holding various professional positions, including in the automotive sector, he joined the bike manufacturer as a Research & Development Engineer. In this role he is responsible for the system integration of the drive units. As a passionate mountain biker, he is mainly on the road in southern Hesse and Liguria.