Page:Popular Science Monthly Volume 92.djvu/489

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��COWWUTATOR

��The machine is now ready to be fitted with brushes. The brush system de- scribed as follows, like the armature, can be used on any type of machine — series, shunt or compound. The brushes are made from very thin sheet copper bent as shown in the sketch. They are mounted on a small fiber or hard wood block of the dimensions shown. Small brass machine screws hold them in place and also provide means for connections. Care should be taken in adjusting the brushes so they bear flatly upon the commutator surface which reduces the resistance of the sliding contact to a minimum.

After mounting the apparatus on a suitable base, the connections of the various parts are made as illustrated. It will be seen that the field winding is connected in a se- ries with the arma- ture, which fact gives the dynamo its name. An emp- ty thread spool is forced on the end of the shaft to serve as a driving pul- ley. The dynamo

may be driven by a water motor, gas engine or other means. If the ex- perimenter has alternating lighting cur- rent available, a small 110 volt motor may be used to drive the generator. In this case, it makes an ideal motor gen- erator for use on the experimenter's table for electrolysis, etc. A series wound dynamo, however, should never be em- ployed to charge a storage battery as it is very likely to change its polarity and injure the cell.

To build a shunt wound dynamo, it is necessary to make a different field winding. The field winding of a shunt wound dynamo should have a much higher resistance than the armature winding so that it will have suffi- cient magnetizing power without draw- ing too much current. In this case, No. 30 single cotton covered copper wire should be used for the field coils. About

���SHUNT COMPOUND.

COPPER SE&MtNTS BRASS.

RIVETED TO FIBER DISK SCREWS";

���METHOD OF WINDING ARMATURt FI& 1

��Wiring diagrams for the different fields; also the method of winding the armature

��1 2 lb. is the amount needed. It is wound on in the same way, the only difference being that it is connected in shunt to the armature instead of in series with it. The method of connecting a shunt wound dynamo is shown in the sketch. This machine is ideal for charging storage batteries.

Compound wound dynamos are pro- vided with two separate field windings. One winding, which is of fine wire, is con- nected in shunt across the brushes, while the other winding, which is of larger wire, is connected in se- ries with the arma- ture winding. The connections are plainly shown in the sketch. The fine wire should be wound on first and consists of Y^ lb. of No. 30 single cotton covered wire divided equally be- tween the two poles. After being given a coat of shellac, a layer of paper is placed over the winding. The sec- ond T^inding, which consists of ^ lb. of No. 18 single cotton covered wire, is then wound over the first After being shel- lacked, it is covered with friction tape and the machine is assembled.

A very good universal generator can be made by winding each one of the three magnets furnished with the magneto. One can be wound for a series dynamo, one for shunt and one for compound. The experimenter will then have a ma- chine of any type by using the correspond- ing magnet over the armature. It is not necessary to arrange any mechanical con- trivance to hold the different magnets in place as they generally fit tightly over the sheet iron frame that covers the armature. It will be necessary, of course, to use the proper connections for each different magnet.

These small generators, if properly constructed, should deliver from 20 to 30 watts of energy. This will depend largely upon the strength of the magnets.

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