Electric crane controllers

Other papers in the series on electrical apparatus for cranes deal with the requirements as to motors and auxiliary equipment; the latter comprising brakes, overload protective panels and limit switches. This paper on controllers reviews its subject in a general way, without going into any details of the devices employed, presenting a clear view of the fundamental considerations involved. The controlling apparatus of an electric crane is responsible for the prompt and proper accelerating of the several motions; their speed control; the safeguarding of the motors from abuse; the convenience and economy of operation; and the elimination of many dangers due to carelessness. The author touches indirectly on these points but concerns himself chiefly with the character of the controllers best suited to the bridge, trolley and hoist under various conditions. The paper deals fully with the problems concerning the selection of ohmic values for the resistors and also covers very completely the connection arrangements and resistance values involved in the dynamic braking control of lowering loads.