S and S' is the secondary winding of the transformer, with a tapping t midway, joining it to a series circuit containing two alternating current electromagnets E and E', whose cores are connected by the long soft iron yoke Y. Pivoted at P' is a steel bar SB, which is polarized by the two coils C and C' the current being supplied by a cell A. Fixed rigidly to SB, and moving with it, is a double contact piece CP with platinum contacts opposite similar ones on the fixed studs CS, CS'.
CP is flexibly connected through F to one of the direct current terminals T, to which also are joined up one coating of each condenser K and K'.
Fig. 2,121.—Diagram showing essential features of Premier Ampero electromagnetic rectifier. Details of construction and principles of operation are given in the accompanying text.
The other direct current terminal T' is connected to the center of the transformer secondary at t; and CS and CS' are respectively joined up to either end of the secondary winding and to the other coatings of the condensers.
Fig. 2,122.—Diagram of General Electric (Batten) electromagnetic rectifier. It is desirable for light and occasional service, where direct current is required but only an alternating supply is available, being used for charging storage batteries, exciting spark coils, performing electrolytic work, etc. The rectifier consists of a step down static transformer T, by means of which the circuit pressure is reduced to about 50 volts; also, a polarized relay R, the contact tongue C of which moves to one side or the other in sympathy with the alternations of the current in the primary winding P, the secondary current induced in the winding S being thereby rendered direct in the outer circuit. T', T' are the main terminals which are connected to the alternating current supply through the wires W. Lamps inserted at L are used as resistances in the primary circuit, the reduction of the voltage already alluded to being effected by this means. In charging storage batteries where a low pressure is required, a lamp (or lamps) should be connected in the secondary circuit as shown, S B being the storage battery, and L' L' the lamp resistances in series therewith, the battery has one end of the secondary S connected to its middle. Thus the alternating current leaving the transformer by the wire 1, passes by flexible connection 2, to the vibrating contact tongue C of the relay, the latter causing the currents in either direction to flow through the two halves H, H' of the battery, whence the current re-enters the secondary of the transformer by the wire 3. The soft iron core of the relay is in two halves S' S' and the armature A, carrying C, vibrates between their polar extremities. M, M' are two permanent magnets with their like poles together at the center C' where A is pivoted. Supposing these poles are north as indicated, the extremities of A will be south. The south ends of M, M being in juxtaposition with the centers of the soft iron cores S', S' will render their extremities facing the ends of A of north polarity. The windings on S', S' are connected in series with each other, and in shunt with P across the main terminals T', T'. Then because of the polarization of A and S', S', the former will vibrate rapidly in sympathy with the alternations of the current. K is a condenser shunted by a lamp resistance L", this being found to improve the working of R.
When the alternating current circuit is broken, the springs SP, SP, carried by SB and bearing against the adjustable studs, keep SB, CS and CS'. The apparatus thus acts also as a no voltage circuit breaker, for should the supply fail, the storage battery A' under charge will be left on open circuit.