How to Replacing Dynamo Brushes

How to Replacing Dynamo Brushes

Here you can get How to Replacing Dynamo Brushes. Here we provide Dynamo Brushe Removing, Refitting brushes, Inspecting and Cleaning commutator.

Undo the screws holding the brush cables. Push the spring to one side and remove the brush. Before refitting the endplate, push the end of the coiled spring from the top to the side of the brush to wedge it in the holder.

Removing the brushes

The carbon brushes are a sliding fit in oblong holders on the dynamo endplate. Coiled springs bear against the tops of the brushes to carry them in contact with the commutator. Each brush also features a braided wire or cable attached by a screw. The cable from one brush results in earth, which from the opposite to the dynamo output terminal.

Undo the screws holding the cables, push the ends of the coiled springs to one side of the brush holders, and pull the brushes out. Note exactly how they were fitted, so that if you refit an equivalent ones later, each goes back as before. If a brush is reversed, it’s going to not seat properly on the commutator. Measure the length of the brushes. If the carbon is worn down to a thickness of in. (10 mm) or less, fit new brushes.

However, even if the carbon thickness is down to in. (13 mm) it’s still best to exchange the brushes. If the brushes aren’t too worn they’re normally about 1 in. (25 mm) long – they’ll are sticking in their holders and not contacting the commutator properly. Use a fine file to remove any raised spots from the surfaces of the brushes. Clean out the holders with a petrol-soaked rag. Replace them in their holders and check that they slide freely and do not rock from side to side.

Refitting the brushes

Always clean the brush holders thoroughly before fitting new brushes. The ends of the brushes must be shaped to match the curve of the commutator. If they’re not, remove the armature and wrap fine glasspaper around it, abrasive side outwards (do not use emery paper). Fit the endplate over the commutator, and switch it in order that the brushes bear against the glasspaper and are shaped to match the curve of the commutator.

Replace the brushes in their holders and reconnect their cables to the output and earth terminals. Check that the brushes are a smooth, sliding slot in the holders. If they’re too loose they could tilt and jam within the holders. Make sure the brushes don’t stick out of the inner ends of the holders. Wedge them in situ by adjusting the ends of the coiled springs in touch against the edges of the brushes rather than the top.

Doing so enables you to refit the endplate and brush-holder assembly without damaging the inner ends of the brushes, which might otherwise catch on the commutator. With the endplate refitted, reassemble the dynamo with its two long bolts. Take alittle screwdriver, and dealing through the ventilator holes within the endplate (or the inspection ‘windows’), move the ends of the coiled springs from the side of every brush to the top, so pushing it down into contact with the commutator.

Inspecting the commutator

  • Glazing: The commutator segments have a varnished look. This coating may be due to dust and water inside the casing, or to particles worn from the brushes or the mica insulation strips between segments.
  • Scores and pits: Usually pitting and scoring of the commutator segments are caused by electrical arcing between the commutator and badly fitted, poorly seating or worn-out brushes.
  • Melted solder: Overheating can melt the solder connections between the segments and the armature windings. Sever cases show as a ring of melted solder around the inside of the casing.
  • Faulty insulation: The mica strips stick up between segments, stopping the brushes making contact. This is caused by wear or arcing removing surface copper. One of the segments has also cracked.

Check the condition of the commutator whenever you remove the dynamo from the car – even if you’re doing so only to examine the brushes. The job is best through with the armature faraway from the dynamo. Remove the top plate . Scratch alignment marks on the front plate and casing to make sure that they will be reassembled correctly later. Push out the armature, along side the front plate and pulley. Wipe the commutator clean with a petrol-moistened cloth and inspect it thoroughly.

Major defects to seem for are glazed, scored and pitted segments, or faulty insulation between them; soldered connections that have broken or melted together; and segments that have come loose. All but the loose segments are often repaired fairly easily, so long as they’re not too worn or badly damaged. Even loose segments are often re-soldered, but that’s delicate work which has got to be through with a powerful soldering iron due to rapid heat loss through the copper. it’s best left to an auto-electrician.

Cleaning the commutator

Grip the whole armature in a vice fitted with padded jaws. Put a strip of fine glasspaper – not abrasive – over the commutator during a half loop, then pull the ends of the strip backwards and forwards until the copper becomes bright and clean. Rub evenly all round the commutator and along its length.

If the commutator is just too worn or damaged for this treatment, you’ll be ready to have it skimmed on a lathe. Consult an auto-electrician. After cleaning or skimming, the mica insulation strips between the segments may have curtailing , as they’re going to be level, or nearly level, with the faces of the segments. They should be about 1mm below the extent of the faces. If they’re higher cut them back evenly along the entire length of every strip to offer an honest square groove.


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