Carbon Brushes

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Information @ a Glance

  • A brush is a device which conducts current between stationary wires and moving parts, most commonly in a rotating shaft. Typical applications include electric motors, alternators and electric generators.

  • There are distinguished basically three types of carbon brushes: brushes for automotive applications: Direct Current, voltage 12-48 V, brushes for household applications: Alternating Current, voltage 110 / 220 V,
    brushes for industrial motors: both Alternating Current and Direct Current, various voltages.

  • Exact composition of the brush depends on the application. Graphite/carbon powder is commonly used. Copper is used for better conductance (rare for AC applications and not on automotive fuel pumps which run on carbon commutators).

  • A carbon brush is typically constructed of carbon with an amorphous structure or graphite which is an allotropic form of carbon.

  • Brush sizes are designated as Thickness x Width x Length of the carbon.It performs both an electrical and a mechanical function within a system. It is a conductor of current in an electrical circuit and it is subjected to mechanical forces as it makes physical contact with a surface in motion.

  • Successful carbon brush operation is dependent on many factors but the primary factor is proper contact and mechanical stability.

  • Copper powder is generally used for the manufacture of carbon brushes applied in low voltage motors.

  • In order to increase service life and to minimize susceptibility to electromotor failure, the carbon brushes must be guided with low friction and wear and without burring.

  • A basic requirement for problem-free movement of the carbon brushes is a smooth and well-designed precisely dimensioned sealing technique.

  • A carbon brush for discharging static electricity of protecting semiconductor devices from damage by the discharge of static electricity from the semiconductor devices.

  • To characterize carbon and graphite materials used for carbon brushes, it is sufficient to state the following material characteristics: Specific Electrical Resistance, hardness and bending strength and bulk density.

  • The specific electrical resistance (SER) of a carbon brush that can be used in a starter motor is greater than 1000µcm, the SER of a carbon brush that can be used in an auxiliary electric motor or an alternator is greater than 10,000µcm, and the SER of a carbon brush that can be used in fuel pump motor is greater than 20,000µcm.

  • The carbon brush assembly includes a carbon brush, a carbon brush seat, a constant force spring and a cover.

  • A constant carbon brush pressure also can maintain proper contact between the carbon brush and a connecting portion to prevent poor electrical contact and generation of sparks.

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