popular mechanics - homemade dc generator

8/16/2019 Popular Mechanics - Homemade Dc Generator

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Building an Electrical Generator

BY B. FRANCIS DASHIELL

ient. The draft is produced by slantingthe surfaces from the center linetoward the edges, to form a slightcrown, like that on the face of a pulley.

The bearings, shown in Fig. 3,

HE making of a small electricalgenerator affords experience in

mechanical and electrical constructionthat is both interesting and practical.The generator described in this articleand shown in detail in the illustrationswas designed to be made with compara-tively simple machine processes and a

minimum use of special tools ordevices. It is a 100-watt, direct-cur-rent, shunt-wound machine, and theparts are worked out to give a highstandard of mechanical practice aswell as to withstand hard service. If machine-shop facilities are not directlyavailable, the machining may be donein a commercial shop at small cost.The materials are those in commonuse for such work, and readily avail-able from dealers.

The making of the patterns and cast-ings should be undertaken first, andonly after a close examination of the

working drawings in the page platehas been made. The perspectivesketch and the assembly views, Figs. 9and 10, show the general constructionand the arrangement of the parts. Thepatterns are of simple design, andmay be made by one familiar with theuse of ordinary woodworking tools.

Patternmakers' white pine is requiredfor the patterns; glue, screws, brads,and other common means of fasteningwooden parts, may be used for this pur-pose. All nail or other holes in the sur-f b l d f ll Th

T

This Direct-Current Generator was Designed to beMade with Comparatively Sim ple Machine Processes

appear similar in the top view H, butthat shown at F is 1.875 in. wide, andthat at G, 3.375 in. wide. They are builtup of five parts each, as indicated, andallowance must be made for finishingthe castings to the dimensions shown.

The field magnet is cast from the

pattern in gray iron of a fine texture,and the bearings are cast in hardbronze. Iron bearings must not beused under any circumstances.Examine the castings thoroughly and

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f t b l d f ll Th j h if h h fl

2834 P O P U L A R M E C H A N I C S

upright on their bases and drill .375-in.holes in the shaft-bearing hubs. Thendrill the two holes in each of the bases

to fit the .312 cap screw J, to pro-vide for the fastening of the bearingsto the poles.

The commutator, detailed in Fig. 7,is made as follows: Select a piece of round hard-rubber rod, 1 in. long and1 in. in diameter. Drill a ½-in. hole

through the center for the shaft. Forcea piece of brass or copper tube, of .125-in. wall and 1-in. inside diameter, overth is core. Tap the tube and core toreceive 12 No. 4 .11-in. diameter stand-ard fillister-head machine screws.Place six of them at each of theends, .125 in. in, and space them equally,60° apart. The screws are like thatshown at K. Divide the tube into sixequal segments by making kerfs witha hacksaw, lengthwise between thescrews. Each segment is thus insu-

lated from the others by air gaps.The armature and shaft assemblyare detailed in Fig. 6. The armatureis built up of laminations in the formof disks, cut from thin sheet iron, 2.938in. in diameter, as shown in Fig. 5.Each disk has twelve .375 by .375-in. open-

ings cut into its edge, spaced equidis-tant, 30° apart on center radii. Puncha ½-in. hole in the center of each andstack them up to form a compact pile,3 in. high. Place them in a charcoalfi d h h b i h d

machined sides of the poles withaccuracy. If the armature is found tobe out of balance, cut it down or file

it slightly in a lathe. Wrap a piece of heavy paper around the armature andfit it into the tunnel snugly. Slip thebearings on the shaft ends, and fitthem against the surfaces. Takingcare that they do not slip or becomedisplaced, slightly mark the centers of

the fastening holes in the pole sur-faces with a center punch inserted inthe holes. Drill and tap the holes forthe screws J. The armature shouldrotate freely when the bearings arefitted into place. Drill oil holes intothe hubs from the upper side, and fitthem with cups if desired.

The brushes and brush holders usedon this generator are of interestingdesign, as shown in Figs. 4 and 8. Makethe holder of a piece of copper or brassangle, ½ in. wide. Solder together

three or four strips of thin phosphorbronze at their top edges and drill andtap them for an 8-32 machine screw.Bolt this to the vertical leg of theholder. Drill and tap the lower end of the same leg similarly for an adjustingthumbscrew, with which to move the

brush to or from the commutator.Drill the other leg as shown in Fig. 8,for a machine screw, as in Fig. 4, at L.The method of insulating the brush isindicated in Fig. 8. Two fiber, or hard-

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BEARING

FIBER

WASHER

NO.4 MACH. SCREWK

ARMATURESHAFTASSEMBLY

BRASSSEGMENTS

COMMUTATOR

TUNNEL

CORES

POLES

TAP FOR

NO.12 SCREW

G

F

BEARINGS

CAP SCREWBRUSHANDHOLDERARMATUREDISK

NO.4 MACH.

SCREW

L


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POPULAR MECHANICS2836

shellac. The cores are thus providedwith an insulating cover. Permit theshellac to dry before winding the coils.

Prepare the armatu re core by pastinga circle of heavy paper to each end of

vent breaking and to provide properinsulation.

The winding of the arma tur e is morecomplicated than that of the field mag-net, but should present no serious d i f f i -culties if the directions are observedstep by step. The process, as shownin Fig. 12 , is as follows : The arma tureis held with the commutator endtoward the body of the worker, and the

roll of wire is placed conveniently onthe workbench. Procure 1¾ lb. No. 20gauge single cotton-covered wire forthis purpose. Start the winding in slotNo. 1, passing the wire away from thebody through the length of the slot,over the opposite end of the armature,

and returning the wire in slot No. 2.Continue this winding until the slotsare full, which requires about 80 turns.None of the wires must be above theslots or they will interfere when thearmature is placed in the tunnel. Turnthe armature halfway around to bring

slot No. 3 uppermost. Wind as before,passing the wire around the armaturein slots 3 and 4, beginning at No. 3.Repeat this process in the slots pairedoff, as fol lows: 5 to 6; 7 to 8; 9 to10; 11 to 12. Turn the arm atur e partway around in each case so that thefirst of the two slots being used inwinding is uppermost. All of the wiresmust begin at the bottoms of the odd-numbered slots, and end at the tops of even-numbered slots, on the commuta-tor end of the armature. Cover the

it wi th shellac. When dry, cut out thesquare slots. Paste strips of paper,shellacked thoroughly, into the slotstheir full length, and cover similarly

any other exposed parts that may comein contact with the wire in winding.

The winding of the field magnet maynow be under tak en . Use No. 25 gaugedouble cotton-covered copper wire.

STARTING

END

NO.2OGAUGE

COMMUTATOR CONNECTlONS

FINISHING

END

ARMATURE WIRING

OUTSIDE

N0.25 GAUGE

FIELD WINDING

The Field Winding is Indicated in Fig. 11; theWinding of the Coils around the Armature Core isShown in Fig. 12; and the Connections of the Arma-ture Coils and the Commutator are Shown in Fig. 13


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POP ULAR MECHANICS

of the generator. The commutatormust be set on the shaft so that its seg-ments are centered on six alternate

slots of the armature, and then clampedby means of the nuts. By beginningwith the starting end of the wire inslot No. 1 it may be observed that eachof the starting ends is soldered to theinner screw in the commutator seg-ment in advance of the slot. The start-

ing end in slot No. 1 is soldered tosegment M; the finishing end of thiscoil in slot No. 2 to segment N, etc.The finishing end of the wire in eachcoil is soldered to the commutator seg-ment behind the slot. For example:the finishing end in slot No. 2 is

soldered to segment N; that in No. 12to O, etc. Give the armature and wind-ings a thorough coat of shellac andpermit it to dry.

The generator may now be checkedto see that all preliminary work hasbeen done, and then assembled for test-

ing. Place the armature in the tunneland attach the bearings securely bymeans of the machine screws. Connecta battery of about 12 volts to the fieldfor a minute, magnetizing the poles.Fit the brushes into place, and adjustthem to the commutator. Turn on thebattery again, and the machine shouldrun as a motor. The commutator mustthen be given its final adjustment. If

the commutator has not been set veryaccurately on the shaft, it may benecessary to adjust it slightly so that

its segments are centered properlywith coil-filled slots Nos. 10, 6, 2, 12, 8,and 4, as shown in Fig. 13. The arma-ture should turn clockwise, when theobserver is facing the commutator end.The speed on 12 volts will not be highbecause at least 20 volts are necessary

to obtain full speed. This voltage issatisfactory for test purposes.The generator is now ready to be

run in its normal manner. Fix a pulleyof suitable size to the extended end of the armature shaft, by means of a set-screw. The special local conditions

will determine the size of pulley used.The generator should be run in thesame direction as when it was testedby running it as a motor, as indicatedin the assembly drawing, Fig. 9. Theproper speed is about 2,000 r. p. m.,although it should generate satisfac-

torily, though not to full capacity, atless speed. At full speed it shouldgenerate 25 to 30 volts and fouramperes. Both bearings should be keptwell oiled. Wipe the commutator witha rag dipped in vaseline to keep itbright and clean. The brushes should

be set only tight enough to makea satisfactory contact and collect thecurrent.

popular mechanics - homemade dc generator

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