Carbon Brush for Starter

Spec:4.5x5x9

Carbon Brush for Starter Supplier - Ruian Donghang Trading Co., Ltd. is a professional international trading company specializing in the import and export of automotive electrical components. 

What is a carbon brush ?

A carbon brush, also commonly known simply as a brush, is a critical component in rotating electrical machines like motors and generators. It is a sliding contact that conducts electrical current between the stationary part (stator) and the rotating part (rotor).

Its core functions can be summarized as: Transmit current + Make physical contact + Commutate current (in DC motors).

What are the main functions of carbon brushes

1.         Conduct Current: In DC motors or wound-rotor AC motors, current must be fed to or collected from the rotating windings via the brush.

2.         Commutation (Crucial in DC Motors): In DC motors, the current direction in the rotor coils must constantly reverse to maintain continuous torque. The brush sliding on the commutator bars facilitates this automatic switching.

3.         Collect Current (in Generators): In generators, current induced in the rotating rotor is collected by the brushes from the slip rings and transferred to the external circuit.

4.         Controlled Wear: Made of relatively soft materials like graphite, the brush is designed to wear down in a controlled manner. This sacrificial action protects the more expensive and critical metal components (commutator or slip rings).

Construction & Materials of carbon brush

·         Form: Typically a small rectangular or square block attached to a flexible wire (shunt or pigtail).

·         Main Composition:

o    Carbon/Graphite: The base material, providing conductivity and self-lubrication.

o    Metal Powder (e.g., copper, silver): Enhances electrical conductivity and strength, used for high-current applications.

o    Binders & Lubricants: To reduce friction and minimize sparking.

·         Common Types:

o    Carbon-Graphite Brushes: For general-purpose use.

o    Electrographitized Brushes: Heat-treated for stable performance, very common.

o    Metal-Graphite Brushes (with Cu, Ag): Excellent conductivity, used for low-voltage, high-current applications (e.g., automobile starter motors).

Carbon brushes are found in all brushed or commutator motors:

·         Power Tools: Drills, angle grinders, sanders.

·         Home Appliances: Vacuum cleaners, mixers, hair dryers.

·         Industrial Machinery: Cranes, large DC motors, wound-rotor motor starters.

·         Automotive: Starter motors, alternators (in older designs).

·         Transportation: Traction motors in traditional locomotives and trams.

Carbon brushes are wear parts and require periodic inspection and replacement.

Symptoms of Failure:

1.         Excessive Sparking at the commutator.

2.         Abnormal Noise (chattering, squealing).

3.         Reduced Power or Unstable Operation.

4.         Overheating at the brush holder.

Maintenance Key Points:

·         Regular Inspection: Check remaining length. Replace when worn to about 1/2 to 1/3 of original size.

·         Keep Clean: Prevent buildup of carbon dust and oil on the commutator/slip rings.

·         Proper Seating: New brushes must be "seated" or "bedded-in" to match the curvature of the commutator for optimal contact.

·         Correct Spring Pressure: Pressure must be within specifications. Too little causes arcing; too much accelerates wear.