Electromagnetic compatibility test
Explanation of terms
Like all electronic devices, an E-MTB also generates electromagnetic fields during operation. These are generated by the motor, since it, like any other electric motor, generates its driving force with the help of such fields between the rotor and stator. However, not only the motor causes electromagnetic fields on the E-MTB. The existing power electronics, such as switches, controllers and converters of electrical voltages, can also cause such effects. Likewise, such fields arise around all cables through which current flows on the e-mountain bike. The longer such cables are, the more such effects are amplified.
When designing an E-MTB, engineers must ensure that the electromagnetic fields that inevitably occur do not interfere with the operation of other electronic devices. Likewise, it is necessary to prevent malfunctions on the E-MTB. This can only be achieved if all electronic components of the e-bike are optimally protected from interfering fields emanating from other devices and machines.
In everyday life, you can observe interference from electromagnetic fields very vividly. For example, if you place your cell phone near a monitor when you receive an incoming call. The screen starts to flicker. The cause of this disturbance is the electromagnetic field of the phone. The sudden noise and crackling of the hi-fi system is also a sign that another electrical device in the vicinity is causing interference.
Procedure of an EMC test on an e-bike
The electromagnetic compatibility criteria applicable to E-MTBs are defined in the DIN EN 15194:17 guideline. In this context, it is important to know that every electronic component on the e-bike must comply with these prescribed standards in itself. In addition, DIN EN 15194:17 stipulates that, finally, all system components that a manufacturer intends to market must be tested in combination.
In practice, this means for the producer of e-bikes that not only the motor as an electric drive must be tested for its radiation, and its protection against interference from electromagnetic fields. All components, such as the lighting, the battery and the display, must meet the standards both individually and on the bike itself.
The necessary tests are divided into three areas:
1. Noise immunity test
While the bike is on the test stand, the motor is switched on for support at realistic speed [22.5 km/h]. Antennas are aimed at the bike, which emit an interference frequency in the frequency range of 20-2000 MHz. All measurements are performed both at the front and rear of the bike, 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.
While the bicycle is exposed to the interference frequencies, there must be no changes in the speed of the drive or other system malfunctions above the permissible limits. If these were to occur in practice, the pedelec control system could be impaired and, for example, the motor could unintentionally change its behavior significantly. If you imagine such a malfunction while cycling in road traffic, for example while waiting in front of a red light, such a malfunction quickly becomes a serious danger.
2. measurement of the interference emission
All emissions of electromagnetic fields generated by the e-bike must remain below the applicable limits. Otherwise, radio frequencies, radio equipment or machines, for example, may be disturbed. To test this, the e-bike is set up on a dynamometer and operated with a realistic load of 75% of the rated continuous power. The antennas used to pick up potential spurious emissions from the bike are precisely aimed at the bike and detect emissions in a frequency range of 30-1000 MHz. All measurements are performed on both the left and right sides and in standby mode.
3. ESD - Electrostatic Discharge Test
This test procedure checks whether the electronic components of the e-bike are disturbed by potential differences in the environment and whether their function is impaired. In the test laboratory, this is done with the aid of ESD guns that discharge contact discharges at +/- 4 kV and air discharges at +/- 8 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.
In practice, for example, the cyclist can cause potential differences and disturbances. This is because any person can become electrostatically charged and then cause a discharge of voltage, for example, when reaching for the display of the e-bike. Similarly, all electronic components are connected to the bike. If something changes in the voltage relationship between these components, potential differences that disrupt the function can occur.
The actual measurements and tests can be performed in a comparatively short time and take only a few minutes. However, setting up the test stand and aligning the antennas is much more time-consuming. To ensure that all tests can be performed accurately, the e-bike must be fixed in the correct position on the chassis dynamometer in the measuring room. Changing the antennas for the different frequency ranges is also a time-consuming process.
Backgrounds and challenges
Since the complex EMC tests cannot be carried out in ROTWILD's own development workshop, we work together with renowned test institutes. They have the necessary high-quality measuring equipment and a test bench with mobile cameras. The entire test setup is located in an absorbent measuring hall, where atmospheric pressure, temperature and humidity have to match perfectly.
The speed of development for e-bikes is currently enormous. The demand for test appointments in the independent test laboratories is correspondingly high. This does not make it easy for engineers to find laboratories that still have capacity available in view of the planned start of series production of a newly developed e-MTB.
Since we test all components in a network, it has proven useful to focus on the cable design, routing and shielding. This is because effects from sources of interference can be amplified by the routing of the cables.
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.