GB732408A - Improvements in or relating to electric motor regulating apparatus - Google Patents

Abstract

732,408. Control of D.C. motors; controllers. KAYE, E., and ARNOT, A. E. R. May 4, 1954 [May 5, 1953], No. 12461/53. Class 38 (3). A regulating resistance in series with the armature of a motor is adapted to be placed gradually in circuit by opening a number of contacts in sequence before the motor circuit is broken, the resistance being graded so that, when the motor is carrying maximum current and a contact is opened, the voltage across the contact is less than the minimum arcing voltage of the material of which the contact is made. The contacts for the regulating resistance are mounted on a number of resilient arms 12-16, a further spring contact arm 27 being connected to the armature 29 of the motor. A rock-shaft 37 carries lever 40 bearing upon push-rod 41 which is adapted to engage the arm 27, so that pressure upon accelerator pedal 43 first closes contacts 50, 51, which are made of arc-resistant material. Further movement of the pedal closes contacts 52, 53, and so on -throughout the series until closure of contacts 58, 59 connects the motor directly to the supply battery 32. If the pedal is depressed still further, a push rod 71 opens contacts 73, 74 to insert section 65 of the fieldregulating resistance, and, thereafter, other sections of the field-resistance are inserted in sequence. Stops are provided for limiting the movements of the field-resistance contacts, and stops are located behind the armature contacts to prevent retraction thereof beyond the positions in which they attain an adequate degree of separation. If the pedal 43 is allowed to rise beyond the position at which the contacts 50, 51 open, contacts 84, 85 close to connect a rheostatic braking resistance 86, 87 across the armature of the motor. The braking resistance is reduced by allowing the pedal to rise still further. A reversing switch 94 is interlocked with the rock-shaft 37 so. that it cannot be operated when the rock-shaft is moved to close the motor circuit. For this purpose, the reversing switch has an operating spindle extending at right angles to the rockshaft and carrying a locking disc with two slots, and the rocking-shaft carries an arm which enters one or other of the slots when it is operated to close the motor circuit, Figs. 1, 2 (not shown). If the battery has an output of twenty volts, the stalling current of the motor being two hundred amperes, and it is desired to limit the arcing voltage of the armature contacts, which are made of copper, to twelve volts, then it is arranged that the resistance incorporated by the breaking of the contacts is one and a half times the total resistance already in circuit. Hence, the section 33 has a value one and a half times the armature resistance, and the resistance of the next section is one and a half times the sum of the resistances of the section 33 and the armature, and so on throughout the series.