Automatic Starters

Author: E.E. Kimberly

When hand-operated starters are used by careless or unskilled operators, the controlled device may be damaged by too rapid starting, or the starter itself may be overheated by too slow starting. Automatic starters operated by push-buttons eliminate the personal element of hand-starters and assure proper control of the starting time. Another advantage of automatic starters is the ease with which they may be operated from one or more distant points. Fig. 15-5 shows a typical automatic starter or controller.

Fig. 15-5. Automatic D-C Motor Starter

All types of automatic starters for d-c motors are provided with one or more solenoids which close contacts in order to short-circuit sections of the starting series resistance. Small motors rated at only a few horsepower may be started rapidly, and their starters may short-circuit the starting resistance in only one or two steps. Larger motors require smoother acceleration, and their starters must have many solenoids to short-circuit only small sections of resistance successively. The reversing starter shown in Fig. 15-5 short-circuits the starting resistance in three steps by closing solenoid-operated switches R₂ R₃, and R4 consecutively.