A CHAPTER OF "DON'TS."

"Don't" use waste on commutators.

"Don't" allow copper brushes to remain in contact with with commutators when the machine is at rest.

"Don't" get rattled at all the wires, cables and instruments at the switch board; they are all useful and most of them absolutely necessary, and they are no more complicated than the piping about your plant with which you are now familiar.

"Don't" fail to remember when the belts are put on the machines they are designed to run like any other piece of mechanical apparatus of similar weight and speed.

"Don't" forget to ask the man who is to set up new apparatus to give you printed or verbal directions for running it. If he is a "square man" he will cheerfully do this.

"Don't" fail to read the following, written by an engi neer to a party seeking information.

NOTE. "You will find that there is an armature made to revolve between two or more 'fields, and that as the latter become magnetized they have an attraction that tends to hold the armature from turning, but the belt knows a 'good thing' and 'pushes it along,' thus generating current which the winding carries to the commutator. where it is picked off by the brushes and passed along to the circuit. If your circuit is kept whole and the machine in good order, there is less need of trouble with it than with a buzz saw."

FLASHING OR SPARKING.

In all good dynamos there are certain positions upon the commutator for the brushes at which there will be absolutely no sparking so long as the commutator is kept clean and in good condition. In other dynamos, badly designed or constructed, sparking occurs at all positions, no matter where the brushes are placed, and in such dynamos it is therefore impossible to prevent sparking at the brushes, no matter how well they are adjusted.

When sparking occurs at the brushes of a good dynamo, two kinds may generally be distinguished by the practised eye, viz., those sparks due to bad adjustment of the brushes, generally of a bluish color, small when near the neutral points, and increasing in violence and brilliancy as the brushes recede from the correct positions upon the commutator; and those due to dirty and neglected state of the commutator and brushes, these being distinguished by a reddish color and a spluttering or hissing. When due to this last-mentioned cause, it is impossible to suppress the sparking until the commutator and brushes have been cleaned up. In the former case, the sparks will disappear as soon as the brushes have been rotated into the neutral points.

Another class of sparks appear when there is some more or less developed fault, such as a short circuit, or disconnection

SPARKING AND FLASHING.

in the armature or commutator. These are similar in character to those produced by bad adjustment of the brushes, but are distinguished from the latter by their rot decreasing in violence as the brushes are rotated towards the neutral points. Having distinguished the classes of sparks which appear at the commutator of a dynamo, it remains to enumerate the causes tending to produce sparking. These are

(1.) Bad adjustment of brushes.

(2.) Bad condition of brushes.

(3.) Bad condition of commutator.

(4.) Overload of dynamo.

(5.) Loose connections, terminals, &c.
(6.) Disconnections in armature circuit.

(7.) Short circuits in armature circuit.

(8. Short circuits or disconnections in field magnet circuit.

1. Bad Adjustment of Brushes.-When sparking is produced by bad adjustment of the brushes, it may be detected by rotating or shifting the rocker, by the indication that the sparking will vary with each movement. To obtain good adjustment of the brushes, it will be necessary to rock them gently backwards and forwards, until a position is found in which the sparking disappears. If a position cannot be found at which the sparking disappears, it is probable that the brushes are not placed diametrically apart upon the commutator, or that the neutral points are not situated in their true theoretical positions upon the commutator through some defect in the winding, &c. In this last-mentioned case, the

SPARKING AND FLASHING.

brushes may be strictly adjusted to their theoretically correct positions before starting the machine; then, when the machine is started and the load put on, violent sparking occurs, which cannot be suppressed by shifting the rocker. If, however, one set of brushes only is observed, it will generally be found that, at a certain position, the sparking at the set of brushes under observation ceases or is greatly reduced, while sparking still occurs at the other set. When this position is found, the rocker should be fixed by the clamping screw, and the brushes of the other set at which sparking is still occurring adjusted by drawing them back or pushing them forward in their holders until a position is found at which the sparking ceases, at which they should be fixed. Correct position of the brushes upon the commutator and the suppression of sparking is a matter of great importance, and any time spent in carefully adjusting will be amply repaid by the decreased attention and wear of the brushes and commutator.

The

2. Bad Condition of Brushes-If the contact faces of the brushes are fused or covered with carbonized oil, dirt, &c., there will be bad contact between the brushes and commutator, and consequently great heating and sparking. Simple examination will generally reveal whether this is the case. remedy is to remove the brushes, one at a time if the machine is running, clean, file if necessary, trim, and readjust. If the brushes are exceedingly dirty, or saturated with oil, it will be necessary to clean them with turpentine, benzoline, or soda solution, before replacing.