Electromagnetic emissions with DC motors

Topic:

• How can the electromagnetic emissions of DC motors be minimized?

Solution:

Main sources

The main sources of electromagnetic interference are

• the brush system (arcing because of inductivity and brush vibrations)
• the PWM amplifier

maxon DC motors

maxon DC motors have a relative low tendency to produce arcs, due to

• the ironless winding
• the lower inductance than DC motors with iron cores
• the odd number of collector segments (only one winding segment needs to be commutated at one time)
• the arc reduction by the CLL concept with precious metal brushes

Measures against electromagnetic emissions

There are a number of possible measures that can be adopted to keep the electromagnetic emissions of the drive components as low as possible:

• Use precious metal brushes with CLL rather than graphite brushes, or better yet a brushless motor.
• Install suppression capacitors between the terminals and the ground shield (see Figure below). This is available as an option on DCX motors.
• Install a toroidal ferrite core on the motor leads.
• Suppression directly at the motor is recommended for DC motors without CLL discs.
• Pair motor leads and shield, if possible (also shield the terminals).
• Controllers with a linear power stage produce less electromagnetic emissions on the motor lines than most modern controllers with PWM actuation of the motor.
• Additionally, encapsulate the motor in a grounded housing (the principle of a Faraday cage).