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 



