43 2 



ENGINEERING ON THE FARM 



be decided in order that the size of the storage battery- 

 required may be determined. Note the number of lamps 

 and the number of hours each one is used. It is a foregone 

 conclusion that the standard voltage of no cannot be main- 

 tained in the isolated plant through the medium of a storage 

 battery, because of the cost of the storage battery. A stor- 

 age cell will give about 2 volts; 55 to 60 of these would be 

 required for the no-volt system, and they cost from $3.50 

 to $4.50 per cell. It is, therefore, the practice to use a volt- 

 age of 30, requiring 16 cells. The lamps, of course, will be 

 made for the low voltage. 



Plant equipment. A system for an isolated plant will 

 require the following articles : 



1. An engine with 50' per cent more power than is 

 calculated as necessary to drive the generator. A ^"-kw. 

 generator should have a i}4- or 2-h. p. engine. 



2. A generator, of such size that it will light the whole 

 installation; as a >^-kw., a i-kw., or a 2-kw. generator. 



3. A storage battery, with a number of cells larger by one 

 than half the voltage of the system installed. 



Ammeter, .c/rcwfireeker 



CLK 



f/e/d 'ffreesfe? 



9 9 9 9«_ 



£y/7omo r~/e/c/ 



t 

 House \ ^Barn 



o o 



£o//ery 



After University of Minnesota 



Fig. 329. Switchboard wiring for generator and storage-battery room 



4. A switch board. This may be of slate or marble, and 

 be equipped with the following: (a) a rheostat, to control the 



