628 



Popular Science Monthly 



A Handy Method for Voltage Testing 

 of Storage Batteries 



TESTING a battery of storage cells to 

 determine whether or not they need 

 recharging is a very difficult matter when 

 the batteries are put in an out-of-the-way 

 place not easy to reach. But in just such a 

 case as this, the method described herein is 

 particularly useful. A specially constructed 



1 Z J 



Wiring diagram for voltage testing each cell, 

 and the cross-section of the switch connection 



change-over switch is mounted on the same 

 panel with the voltmeter. The switch con- 

 tains two contact arms capable of being 

 rotated in as many positions as there are 

 batteries to be tested. The voltmeter is 

 connected with the pivot-end of the 

 switch and the individual cells are them- 

 selves connected with the contact-points 

 surrounding this pivot. The contact arms 

 or blades A and B are made of strips of 

 spring brass or copper, and two small 

 blocks of fiber, H and K, are fastened to 

 them by machine screws to keep them 

 apart. The rectangular arrangement so 

 formed revolves about the larger machine 

 screw D, which passes through a hole 

 drilled in the center of the block K through 

 a suitable washer E, finally into another 

 hole in the panel M. The two nuts, P, 

 hold the screw D in position and at the 

 same time provide a means for attaching 

 an electrical connection. The blade B is 

 electrically connected with the screw D 

 by means of the connecting strip F, as 

 shown. The blade A makes another out- 

 side connection through the circular brass 

 ring 5 and the brush G which touches it 

 no matter in what position the blade hap- 



pens to be. The connection with the ring 

 5 and the connection with the screw D 

 lead to the respective terminals of an ordi- 

 nary I- to 3- volt voltmeter. 



The contacts surrounding the pivot of 

 the switch are made of machine screws 

 and are spaced apart from each other a 

 distance equal to the distance between the 

 two blades A and B. This switch requires 

 the number of contacts to be only one more 

 than the number of cells that are connected 

 in series. The connections are made with 

 the contact-screws in the rear of the panel, 

 and adjacent contacts are connected with 

 adjacent posts on the cells, as shown in the 

 diagram of connections. From this diagram 

 it is evident that when the blades are in 

 the position i, the voltmeter will be con- 

 nected with cell number i. In the position 

 2 shown in the diagram, the voltmeter will 

 be connected across cell number 2; and 

 so on. Thus, in testing each cell, it is only 

 necessary to turn the switch. 



How to Handle Hard Rubber to 

 Prevent Its Breaking 



HARD rubber is one of the materials 

 most frequently used by the electric 

 experimenter; first because of its excellent 

 insulating qualities, and second, because it 

 is easier to handle than porcelain or similar 

 hard materials. Nevertheless, a great deal 

 of the material is often wasted before the 

 desired results are accomplished, because 

 care is not taken in the working of it. 



Hard rubber can be cut without chipping, 

 with a hacksaw or a fine-tooth saw if the 

 cut is made more than half way through on 

 one side, then started on the other side 

 until the first cut is met. The pressure on 

 the saw should be very light or the rubber 

 will crack. Rubber can be drilled with 

 ordinary twist drills in a drill-press; but 

 the stock should be laid on a perfectly flat 

 surface and a very light pressure applied 

 on the drill. When finishing a base it is 

 often desirable to have the edges rounded. 

 This can be done with fine sandpaper. To 

 obtain a dull finish on the surface it should 

 first be sandpapered and then washed. A 

 brighter finish can be obtained by mixing 

 a little emery with oil and polishing the 

 surface. 



When working hard rubber in a drill- 

 press it is best to have it fastened to a 

 solid support so that the drill will not bend, 

 or the material lift up with the turn of the 

 tool. — Alexander V. Bollerer. 



