Patent GB-190914980-A (GB)
Title: Improvements relating to the Rectification of Alternating Electric Currents, and to Devices for use therein.
Inventor: FAESSLER ERNST
IPC: H02M7/36
Filed: 1909-06-26
Granted: 1910-06-16
Abstract: 14,980. Fõssler, E. June 26. Commutator switching - arrangements. - A rectifier having a vibrating contact-carrying armature and an operating-magnet excited by rectified current has means to determine the direction of the rectified current delivered. The natural frequency of vibration of the armature is adjusted to be slightly greater or slightly less than that of the supply current, the former if the armature closes circuit at the end of its inward movement, and the latter when closing circuit after its outward swing. Such an armature will only operate with a given excitation, and by means of a direct-current electromotive force superposed upon the rectified exciting- current, or supplied to a second coil on the magnet, the direction of the rectified current may be determined. In Figs. 2 and 5, the alternating current is applied at the terminals 11, 12 and passes as rectified current round the magnet 19 through the armature 22 and lead 24 to the battery 27, returning by a lead 13. The rectifier in each case operates to deliver current in opposition to the direction of a discharge from the battery, the arrangement being such that only so will the requisite exciting-current pass through the magnet coil to oscillate the armature with the frequency of the supply current. The natural frequency of the oscillating system is generally adjusted to differ about 10 per cent from that of the supply current. As shown in Fig. 2, the whole of the current passes through the exciting-coil, but, by shunting this with an equivalent inductance, a portion of the rectified current may be used. As shown in Fig. 5, the terminals 15, 17 are connected to an auxiliary winding 33, in which the battery generates a flux in opposition to that produced by the rectified current. Such an arrangement may be employed for charging two voltage batteries from a supply of higher voltage. Fig. 4 shows a modified arrangement to supply a circuit which does not contain sufficient back electromotive force to determine the direction of current. The necessary auxiliary electromotive force is furnished from a battery 31 arranged with the magnet coil 19 in a circuit fed with rectified current in parallel with the main circuit 30. A compensating- resistance 32 is included in the main circuit to preserve identity of phase in the parallel circuits. The combination of rectified and continuous currents as described above effects a shortening of the duration of the electromotive force it is required to deliver, and lengthens the remaining portion of the cycle. Consequently, the construction shown in Fig. 6 is adopted. The spring 21 on which the armature 22 is mounted is clamped between adjustable plates 38, 39 so that the free length of spring for vibration on one side of the median position exceeds that for the other portion of the swing. The " fixed " contact 42 is similarly mounted upon its spring 43, between a bracket 44 and an adjustable plate 45. The armature 22 carries an adjustable contact 41 and an adjustable stop 50. Below the median position of the armature, the two springs 21, 43 are in action and produce a relatively rapid movement of the armature to shorten the duration of contact; above the median position, the spring 21 alone operates, and the armature moves more slowly. The bracket 44 is itself adjustable. The instant of maximum deflexion of the armature would synchronize with the instant of maximum exciting-current but for the hysteresis of the magnet. To counteract this and obtain sparkless operation, the contacts 41, 42 in the construction shown in Fig. 6, move in different paths, so that the friction between them may cause a corresponding braking action on the armature; by suitably setting the contact spring, or by means of a suitable brake, oil or air dash-pot, or magnetic eddy-current brake attached to the armature and arranged for regulation, the effect of friction may be adjusted.