Page:Popular Science Monthly Volume 91.djvu/166

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150 Popular Science Monthly

Steadying the Voltage of a Dynamo Driven by Gasoline Engine

THIS problem has been solved in various ways. We are all familiar with the storage-battery system, and being ac- quainted with this system, realize its ex- pense. If a gas or gasoline engine is to be used to drive a

Cast iron "fly-wheel **v

��dynamo, some provision must be made to steady the speed of the dynamo.

���A spiral spring in flywheel hub on an armature shaft to prevent flickering of lights

Every time the engine ex- plodes, there is a momentary increase in the speed of the dynamo, causing a fluctuation of voltage, and a flicker of the lamps. Special engines with extra heavy fly-wheels have been built for this purpose, which give fair results, provided that the armature of the dynamo has a large moment of inertia. If a flywheel is put on the dynamo, the voltage fluctuation is lessened, but this induces belt slipping, and hence loss of power. Specially built electric lighting engines are expensive, and for small plants of from one-half to two or three kilowatts give but little satisfaction.

The writer has obtained satisfactory re- sults in a one-kilowatt plant by using the spring flywheel arrangement shown in the diagram. The belt from the engine drives the pulley on the flywheel which is fastened to the pipe. The pipe in turn twists the end of the helical spring. The other end of the spring is fastened to the flywheel. In this way the impulses from the engine are spread over a longer interval, and the tendency is for the dynamo to run at a constant speed. The whole spring is packed in grease, so that there is but little loss of power from friction. Belt slipping is avoided by the freedom of motion of the pulley and pipe. The momentum of the dynamo flywheel tends to keep the speed of the dynamo constant while the engine

��is slowing down on the compression stroke, and likewise while the engine is on the power stroke, the spring operating as an elastic medium between the driving pulley and the flywheel.

The spring must be made of steel of exceptionally good quality, on account of the rough usage to which it will be exposed. I used a No. io-gage spring steel wire. This wire was made up into the form of a coil spring and then tempered. A spring was tried which was made of spring steel which had been tempered before it was made into the spring. This spring lasted but a few hours, after which time it was distorted beyond usefulness.

The results with the spring were com- pared with those without the spring, by first running the machine with the pipe clamped fast to the flywheel spindle, and then running the machine with the spring free to operate. In the first case there was a variation of between three and four volts upon each explosion of the engine; in the second case this variation was reduced to less than one volt, the plant operating at HO volts. The power losses arising from this arrangement were negligible.

��CARDBOARD INSULATOR

��Increasing the Voltage of a Dry Battery

OFTEN a battery of dry cells will fall in voltage or become reduced in pressure because some of the cells have polarized, consequently the current is not sufficient to operate the ig- nition of an en- gine or to per- form its duty. Such an occur- rence is likely to prove very an- noy i ng . In emergency cases the voltage can be increased temporarily by taking a good cell from the set, cutting it in half and then making the connections as shown. Slip the container out of its casing to make the cut and connections, then put the two parts back so that the cell will have the same appear- ance as before. This reduces the ampere hours, but it bridges over the difficulty.

���CARDBOARD INSULATOR WITH HOLE CUT IN CENTER

A good cell cut in half to produce more voltage

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