GB519114A - Improvements in or relating to electric motor controllers - Google Patents

Abstract

519,114. Control of D.C. motors. WEST & CO., Ltd., A., and DAVID, O. T. Aug. 15, 1938, No. 24013. [Class 38 (iii)] The shunt field 3 of a motor 1 is not strengthened to its full value during return of the controller to the "off" position and thereby regenerative action is prevented, although the field 3 is so strong as to overpower the series field 2 during rheostatic braking During forward movement of the controller, resistances R1, R2, R3, R4 are successively shorted there being an intermediate stage when R1, R2, R3 are all in parallel and in series with R4, thereafter R6, R7, R8 are successively inserted and finally contactor C8 opened. During return movement, normally closed contactors C5, C6 are maintained energized by holding contacts thereon until the "off" position is reached, and thus resistances R6, R7 are kept in circuit with the field 3. During rheostatic braking, resistances R2, R3, R4 are in circuit with the armature and series field 2, and the field 3 is excited strongly with contactor C6 closed or fully with contactor C5 closed. The opposition between the fields gives a braking effort/speed characteristic with a maximum at a predetermined speed.