AN ELECTRIC VEHICLE CHARGING PLANT. 



Bv John Wilkinson Kirkland, M.AniT.E.E. 



(Plates 18-19 ^"^ •^'"'' ^''-^'^ fi9">'<^-) 



The i)urpose of this brief paper is to describe and illustrate 

 a successful and economical charg-iiig plant for electric vehicles 

 which has ])een installed at Johannesburg. It is believed that 

 this is the largest electric charging station south of the Equator. 

 No general or specific arguments as to the economy of such 

 vehicles are advanced, but the practical arrangements of charg- 

 ing apparatus and control are dealt with. 



The problem was to design and btiild from materials locally 

 available apparatus wdiich would enable a large number of elec- 

 tric vehicles to be charged simultaneously by means of the 460- 

 volt direct current municipal supply. The largest vehicle planned 

 for requires for charging 75 amperes at 115 volts, and the 

 smallest syV^ amperes at 60 volts. 



It was decided to instal a 4-unit balancer set consisting of 

 115-volt direct-current shunt-wound generator, and to^ derive 

 from this machine four 115-volt circuits. The set as erected is 

 shown in Plate iSb. Each machine is rated at I2y< kw., and the 

 speed is ,800. (The fifth machine, on the left, is a s])are, and is 

 not connected up either mechanically or electrically. ) These four 

 machines as originally furnished had shaft extensions at one end 

 only. It was necessary, therefore, to weld extensions to two of 

 the shafts, and this was successfully done by the electric arc 

 process. The machines are connected by flexible couplings of 

 the leather strai) type, and are mounted on a heavy timber base. 

 A single starting rheostat, with low voltage release, is employed, 

 and a direct-current circuit breaker protects the set and the 

 system from overload. An ammeter (300 amperes) and a volt- 

 meter ( 750 volts ) are also provided, as may be seen in the picture. 



All of this apparatus is installed on the first floor of the 

 charging garage, and heavy insulated circuits are run thence to 

 the ground-floor, where there is a distribution and control switch- 

 board. This board was built locally in Johannesburg, and has 

 four main sections, three of which are now equipped for four 

 circuits and one for six circuits. When required the board can 

 be completed for 18 circtiits by adding switches for two more 

 circttits on each of three of the sections. Plate i8a shows the 

 general arrangement and appearance o^f the board. 



Fig. I is a general wiring diagram of the balancer set and 

 switchboard. Each of the four 115-volt circuits derived from 

 the balancer is connected to busbars through a reverse current 

 overload circtiit and through a main ammeter. A voltmeter also 

 shows the busbar voltage. Immediatel}^ below these main instru- 

 ments are the circuit ammeter and voltmeter, one of each being 

 sufficient to care for all of the circtiits in the section. This is 



