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574 HANDBOOK OF PROJECTION FOR
rectifier use 35 ampere fuses ; for 40 or 50 ampere machine use 55 ampere fuses.
FROM DIRECT CURRENT TO ALTERNATING CURRENT. — In Fig. 184 we see a triple-pole, double throw switch in the center of the panel. By throwing this switch over the tube is cut out and A. C. direct from the lines is supplied to the arc, using the main reactance as an economizer. This is for use in case of accident to the tube. The switch as shown in Fig. 184 is set for D. C.
If the switch is thrown over to A. C. it may be found there is not sufficient amperage, in which case lead 3, Fig. 186, may be moved along studs 1, until sufficient current is obtained. Do not use more than 60 amperes, A. C. The rectifier is built primarily for changing A. C. to D. C, and, while its main reactance may be used as an economizer, that provision is designed for emergency only.
CONNECTING OR ADAPTING LINKS.— The connecting or adapting links, Fig. 184, enable the rectifier to use either 110 or 220 volt supply. To change from one to the other it is only necessary to change the connection of the links. For 220 volt supply they should be connected to the two upper and the two outer lower studs; for 110 volt supply connect to the two upper and the two inside lower studs.
THE DIAL SWITCH.— The dial switch has eleven contacts which are connected to eleven taps on the regulating reactance, Figs. 185 and 186. This connection may be examined in Fig. 186, in which the regulating reactance, 2, has been dropped down to show the connections. This switch enables the projectionist to regulate the amperage at the arc, and any amperage within the capacity of the rectifier may be instantly had by merely moving the switch to the left to raise, or to the right to lower, as per Fig. 184.
THE MAIN REACTANCE, Fig. 184, is nothing more nor less than an auto-transformer. It has three distinct functions, viz.: (a) It adjusts the voltage of the alternating current to the pressure necessary to secure the proper D. C. amperage at the lamp; (b) it supplies a neutral point between the alternating current lines and forms the negative of the direct current lines ; (c) by its reactance it keeps the rectifier tube in operation while the current passes through the zero point of the alternating current wave.
THE REGULATING REACTANCE.— The regulating re actance, Figs. 185 and 186, is nothing more nor less than a