Popular Science Monthly 



949 



and then disconnected and connected in 

 series for use. 



The electrolyte is made of a mixture of 

 sulphuric acid and water. Commercial 

 acid of about 1.835 specific gravity should 

 be diluted with clean rain or distilled water. 

 Mix the solution in some kind of a glass 

 or glazed crock, using the proportion of i 



I CHARGING 



X T I — ' — — ' — — ' — — ' — I I —I L 



^^IT T T T T T 



FI6.5 



PRIMARY 

 BATTERIES ' 



Two groups of primary batteries are con- 

 nected in parallel and eight of the storage units 



part acid to 4 parts water. The resulting 

 mixture should be about 1.180 specific 

 gravity. Always pour the acid into the 

 water in a very small stream, stirring vigor- 

 ously at the same time. When the solution 

 has cooled pour a sufficient quantity into 

 each tube, making the level come to within 

 ]/^ in. of the top of the tube when the 

 elements are in place. 



In usual practice 40 to 60 ampere-hours 

 capacity is allowed for each square foot of 

 positive plate, measuring both sides of the 

 plate. The thickness of the plate, unless 

 great, is disregarded. It is well to 

 know that the electrolyte penetrates only 

 about 1/16 in., so that any excess of 3^ in. 

 in the thickness of a plate is solely for 

 mechanical strengthening of the plate and 

 is useless in an electrical capacity. As the 

 elements of these batteries are round, only 

 the surface can be figured. The tube being 

 ^ in. in diameter and 5 in. long makes a 

 surface area of about 6 sq. in. In allowing 

 50 amperes per square foot, the ampere- 

 hour capacity of one cell of this battery 

 will be about 2. The average charge or 

 discharge voltage is about 2 and the watt- 

 hour capacity of each cell will be 4, thus 

 making a 24-cell battery a 96-watt-hour 

 capacity. While it is possible to draw 

 more current from the battery than is 

 rated, yet it is not advisable to do so, as 

 that ruins it quickly. 



Each cell of storage-battery, regardless of 

 its length, width and number of plates, will 

 give after a full charge about 2)^ volts, and 

 the voltage required to charge any number 

 in series is equal to 2)^ times the number 



in series. Thus, the 24-series battery. 

 Fig. I (since they are all connected in series) 

 will require 60 volts. In the 3-series, 8- 

 parallel battery, three cells are in series 

 and the voltage will be 73^. Usually more 

 voltage than is actually necessary is pro- 

 vided — about 3^ to 5 volts per group. This 

 extra voltage lessens the danger of having 

 the storage cell discharge back into the 

 charging source, the voltage of the storage 

 cell exceeding that of the charging source. 

 The 24-series battery requires about 62 

 volts and the 3-series, 8-parallel battery 

 requires 8 volts. 



To charge a storage-battery with its 

 maximum ampere-hour capacity — that is 

 to say, to charge an 8o-ampere hour battery 

 with 80 amperes for one hour — would 

 probably ruin it. The best rule to follow 

 is to charge at the 8-hour rate. Thus a 

 battery may be charged in 8 hours, which 

 is the normal rate, or it may be .charged 

 in 7, 6, 5 or even 4 hours. In charging this 

 battery the 8-hour or normal rate is de- 

 termined by the cell capacity divided by 

 the 8 hours, which would equal 25. That 

 is to say, each cell is to be charged with 

 14: ampere for 8 hours. The 7-hour rate 

 is 2-f-7, and so on; but under no circum- 

 stance should this or similar small batteries 

 be charged at less than the 4-hour rate. 

 Another good rule to follow is to allow a 

 charging rate of .04 amperes per square 

 inch of positive surface. It is apparent 

 that the foregoing methods of calculation 

 can be used to find the capacity and the 

 charging rate of any size storage cell in 

 common use. 



The resistance necessary to be placed in 



DISCHARGING 



TO AUDION y 



FI66 



When used in a discharge, connections from 

 the battery binding posts are made in series 



series with the battery on a iio-volt direct 

 current main to lower it to 62 volts, the 

 amount necessary for the 24-series battery, 

 will be 192 ohms, for the normal 8-hour 

 rate. In using current from a 220- volt 

 direct current main the same procedure 

 may be carried out to determine the re- 

 sistance necessary to reduce the current to 

 62 volts. This will require 632 ohms for 



