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Page 647 | Volume 2 | Chapter 33 | Care of the Commutator and Brushes

have a tendency to carbonize, and thus cause short circuiting of the commutator, with attendant sparking.

Overload of Dynamo.—It may happen, through some cause or other that a greater output is taken from the machine than it can safely carry. When this is the case, the fact is indicated by excessive sparking at the brushes, great heating of the armature

Figs. 721 to 723. - Method of repairing a large hole burned in two adjacent bars of a commutator.
Figs. 721 to 723.—Method of repairing a large hole burned in two adjacent bars of a commutator. Fig. 721 shows the hole. The first operation is to clean carefully and tin the surface of the hole. The two bars are then wedged apart and mica strips, A B, fig 722, of the requisite size and thickness forced in. The commutator must now be warmed up as much as possible by means of soldering irons, and strips of mica, C, D, E F, fig, 723, placed at the front and back of the hole, being kept in position by pieces of wood W, solder is poured into the hole from a ladle, using a rough mica funnel to guide it.

and other parts of the dynamo, and possibly by the slipping of the belt (if it be a belt driven machine), resulting in a noise. The causes most likely to produce overload are:

NOTE.—In operating dynamos having metal brushes, it is of importance to keep the commutator smooth and glossy. To accomplish this, it is necessary to keep the commutator and brushes clean and free from grit, and to occasionally lubricate the commutator with some light oil, such as ordinary machine oil. This should be done daily if the machine be in constant use. Keep the brushes resting upon the commutator with just enough pressure to insure a good firm contact. This will be found to be much less than the springs are capable of exerting. A good method to follow in cleaning the machine is as follows: Loosen the brush holder thumb screws and tilt the brushes off the commutator (or, if box brush holders be used, take them out of their holders). Then run the machine and hold a clean cloth against the commutator. After the commutator is clean, hold against it a cloth or a piece of waste moistened with machine oil and reset the brushes. If for any reason the brushes begin to cut or score the commutator, it may be readily detected by holding the finger against the commutator; the ridge may be easily felt by the finger. This should be attended to at once in the following manner: Tilt back the. brushes (or if box brushes are used take them out of their holders), and hold lightly against the commutator a piece of No. 00 sandpaper well moistened with oil, passing it back and forth until the surface is perfectly smooth. Then wipe off the commutator with a clean piece of cloth or waste and lubricate with another clean piece moistened with oil and reset the brushes.



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