Brush Arcing
It is the current forced by the winding inductance continuing as a spark in air at the moment the carbon brush passes between commutator segments. It repeats at every commutation, radiates broadband radio frequency noise and wears both the brush and the commutator surface.
The current flowing in the winding cannot be cut abruptly; as the brush leaves a segment, a high voltage appears at the terminals according to V = L·di/dt and the gap ionises to form an arc. The arc uses the motor cable like an antenna and radiates noise extending from kilohertz to hundreds of megahertz.
In the field the most visible consequence of this is the drop in radio remote control range while the motor is running. Suppression methods:
- Fitting suppression capacitors between the motor terminals and from each terminal to the body.
- Slipping a ferrite ring onto the motor cable.
- Twisting the supply and motor cables and keeping them at least 50 mm away from signal cables.
The arc is also an indicator of mechanical life. If you see dark burn marks on the commutator surface, tracking arc marks or excessive carbon dust in the brush holder, the brushes must be renewed and the commutator surface cleaned. Otherwise the contact resistance increases, the motor does the same job with higher current and the driver's current thresholds start tripping early.
The context in which this term is used: DC motor and driver fault diagnosis matrix