How can the electromagnetic emissions of DC motors be minimized?
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).