Checking and replacing alternator brushes

Checking and replacing the brushes is a regular process after dismantling the alternator or voltage regulator and when there are problems in the charging system. Brushes through the sliding rings and transmits power supply to the rotor windings. Power supply to the rotor windings and operation of the alternator depends on correct brushes. In the case of brushes, it is important that they have sufficient length, that the springs push them with a certain force, and that they slide easily in their holders.

After removing the brush holder from the alternator, a visual inspection of the condition is performed. The brushes should be of equal length, the correct shape, and the holder should be undamaged and clean.

Bad brushes can damage the slip rings. Short brushes make weak contact with the sliding rings because the springs cannot press them with the necessary force. There is a high voltage drop and a weaker power supply to the rotor windings. The length of the brush is measured with a vernier caliper. The brush is correct as long as its length is 5 mm above the upper edge of the brush holder. If the brush is damaged or worn, they are replaced in pairs according to the specification for that alternator.

Measuring brush length

There are various types of spring brushes. They can be in the form of a spiral or push rod. Some are part of the holder, separate or delivered together with the brushes. Their condition and thrust are checked. Defective springs are replaced because they do not perform their function of pushing the brushes.

If the brush head, check the condition of the holder, that is, the guide. If necessary, the holder is cleaned or replaced. If the brush after replacing the head, it is necessary to check the diameter of the brush body and possible sanding of the sides. The brush holders must be well insulated from the ground and have a good electrical connection with the brushes. Their electrical condition is checked with a multimeter.

To check and replace the alternator brushes, follow these steps:

Checking and replacing brushes

Perform a visual inspection of the condition of the brushes. Replace damaged or too short brushes with new ones. Measure the length of the brush with a vernier caliper. If the brush is below the required minimum length, replace both with new ones.

Removing the drive belt

Check the condition of the brush spring (length, color…). Check the spring pressure. Replace defective springs with new ones.

Brush holder control

Inspect the holder for cracks, damage, and dirt. Replace damaged supports with new ones. Clean the carrier. Use an ohmmeter to check the electrical connection between the power supply on the holder and the brush. If transient resistance is observed, locate the bad connection and eliminate the malfunction.