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Emissions & Immunity

These installation recommendations are intended to help you reduce electromagnetic emissions (EMI) and improve electromagnetic immunity (EMS) when integrating a battery-powered motor controller into an application.

Important Note on electromagnetic compatibility (EMC) Compliance

The ability to meet EMC/EMI standards depends not only on the motor controller itself but also on the overall application design, including wiring, grounding, enclosure, and surrounding components.

While the motor controller is designed with EMC/EMI performance in mind, final responsibility for passing EMC/EMI compliance tests lies with the integrator or end-user. Proper installation and adherence to the guidelines in this document are essential to achieving compliance.

Prioritization of Standards and Guidelines

In the event of conflicting guidance, always prioritize the source with the highest level of authority and stringency. We recommend following this hierarchy when determining which source to rely on:

Industry Regulations – e.g., ISO, UL, CE, EN Industry Standards – e.g., IEEE, ANSI Application-Specific Guidelines – tailored to the particular use case or product General Guidelines and Good Engineering Judgment – including this article

Power Wiring

  • Use wires with appropriate cross-section. Thicker wires reduce resistance, voltage drop, and heat generation. Always size cables for both current and EMI performance.
  • Keep power wires as short as possible. Shorter wires reduce inductance and minimize EMI and voltage spikes.
  • Twist power wires. This helps reduce radiated magnetic fields by minimizing the current loop area formed by the conductors. E.g.:
    • Twist the battery power leads (B+ and B−) tightly together.
    • Twist the motor phase wires (U, V, W) together.
  • Place ferrite beads on noisy or unshielded wires.
  • Route within the vehicle frame, preferably low and central.
  • Use screened conduit or metal shrouds where structural shielding is insufficient.

Signal Wiring

  • Use twisted pairs
    • For differential signals (e.g., CAN-H and CAN-L), always use twisted pair wiring.
    • For single-ended signals, twist each signal wire with its corresponding ground return wire.
  • Separate power and signal wires. Avoid running signal wires in parallel with power wires. If crossing is necessary, do so at a 90° angle.
  • Use shielded cables for signal and sensor wires. A common practice to prevent low-frequency ground loops is to connect the shield to ground at one end only (preferably on the controller side). Be aware that for optimal high-frequency performance, other grounding strategies might be necessary depending on the specific application.
  • Place ferrite beads on noisy or unshielded wires.

Grounding and Shielding

  • Do not mix signal and power grounds. Keep power ground (B−) and signal ground (GND) separate outside the controller, even if they are connected internally.
  • Use galvanic isolation for sensitive signals. Employ isolated transceivers or opto-isolators for communication lines and sensor inputs that are susceptible to noise.
  • Connect chassis (earth) to B− near the controller with use of a Y-class safety capacitor between the chassis and B− to reduce common-mode emissions.
  • Bond shields and metal enclosures properly. Ensure all shielding and conductive enclosures are electrically continuous and bonded to a known ground point.

Installation Environment

  • Avoid placing the controller near high-EMI sources. Keep the motor controller away from devices like contactors, high-frequency switching converters, and transformers.
  • Mount the controller on a thermally conductive, electrically insulating material if the mounting surface is conductive. The controller's heatspreader is electrically isolated from internal circuitry.
    • For EMI/EMS: If the isolated heatspreader might pick up internal high-frequency noise and radiate it, or be susceptible to external fields, it can be beneficial to bond it to the chassis ground via a Y-class safety capacitor. This provides a path for high-frequency currents, helping to reduce emissions and improve immunity.
    • Safety Considerations: A Y-class capacitor is designed to maintain DC isolation. In the event the heatspreader accidentally becomes electrified (e.g., due to an internal fault connecting it to B+ or B-), the Y-capacitor will block DC flow to the chassis, preventing the chassis from becoming a primary path for battery fault current. Y-class capacitors are designed to fail open-circuit or maintain high impedance under fault conditions like overvoltage, which is critical for safety. They are not, however, designed to act as overcurrent fuses that open due to high DC fault current through them; their primary role is DC blocking and safe failure under voltage stress. Ensure this RF bonding strategy complements the primary chassis-to-B- grounding (often also via a Y-capacitor) for overall system safety and EMC.
  • Mounting in a metal enclosure (metal box with minimal seam lengths and small ventilation holes) can drastically reduce emissions and improve immunity.

Additional Practical Tips

  • Avoid sharp bends in cables. Sharp bends can damage conductors or shielding, alter the cable's intended electrical characteristics (e.g., impedance, balance of twisted pairs), and potentially degrade signal integrity or shielding effectiveness, reducing reliability.
  • Secure all wiring. Prevent cable movement and vibration using cable ties or clamps to avoid intermittent connections or radiated noise.
  • Employ consistent routing and placement of cables to avoid introducing unintended EMC issues.
  • Terminate unused signal inputs. Avoid leaving digital or analog inputs floating; connect them to a defined logic level or use pull-up/pull-down resistors.
  • Ensure good connector contact. Use high-quality connectors. Make sure contacts are clean, tight, and corrosion-free to avoid noise or failure.
  • Ensure good grounding. Ground loops, especially when using shielded cables, can induce unwanted currents.
  • Devices with significant capacitance to chassis can unintentionally introduce EMC issues.

By using a holistic approach, you can significantly improve EMC/EMI performance, reduce interference risks, and enhance the reliability of the motor control system in real-world installations.