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Learning Objectives: After reading this CONTENT, YOU MUST be able to:
1. Define Drum Controllers.
2. Draw diagrams for Drum Controllers.
3. Develop safety awareness in the workplace
This information will cover the importance of Drum Controllers in Manual Starting of DC Motors. This will also cover the circuit diagrams for Drum Controllers in Manual Starting of DC Motors .
DRUM CONTROLLERS
Series and cumulative compound motors are often used on cranes, elevators, machine tools, and other devices where the motor is under the direct control of an operator and where frequent starting, varying speed, stopping, and reversing are necessary. A manually operated controller that is more rugged than a starting rheostat is used in these applications. This starting rheostat is called a drum controller.
DRUM CONTROLLERS
DRUM CONTROLLERS
A typical drum controller is illustrated in Figure 22–10. Inside the switch is a series of contacts mounted on a movable cylinder. These contacts, insulated from the cylinder and from each other, are the movable contacts. There is another series of contacts, located inside the controller, called stationary contacts. These contacts are arranged to make contact with the movable contacts as the cylinder is rotated. On top of the drum controller is a handle that is keyed to the shaft for the movable cylinder and contacts. This handle can be moved in either a clockwise or a counterclockwise direction, providing a range of speed control in either direction or rotation. Once set, a roller and notched- wheel arrangement keeps the cylinder and movable contacts stationary until the handle is turned by the operator
A schematic of a drum controller having two steps of resistance is shown in Figure 22–11. In this wiring diagram, the contacts are shown in a flat position to make it easier to trace connections. For operating in the forward direction, the movable contacts on the right connect with the center stationary contacts. For operation in the reverse direction, the movable contacts on the left touch the stationary contacts in the center.
There are three forward positions and three reverse positions in which the controller handle can be set. In the first forward position, all resistance is in series with the armature. The circuit for the first forward position is traced as follows:
1. Movable fingers A, B, C, and D contact the stationary contacts 7, 5, 4, and 3.
2. The current path is from 7 to A, from A to B, from B to 5, and then to armature terminal A1.
3. From A1, the current path is through the armature winding to terminal A2, then to stationary contact 6, and then to stationary contact
4. From contact 4, the current path is to contact C, to D, and then to 3.
5. From 3, the current path is through the entire armature resistor, through the series field, and then back to the line.
In the second forward position, part of the resistance is cut out by the connection from D to E. The third forward position bypasses all resistance and puts the armature circuit directly across the source voltage .
In the first reverse position, all resistance is again inserted in series with the armature. Figure 22–12 illustrates the first position of the controller for the reverse direction.
The current in the armature circuit is reversed. However, the current direction in the shunt and series fields is the same as for the forward direction. As shown earlier, changing the direction of the current in only the armature changes the direction of rotation. In the second position, part of the resistance circuit is cut out. The third reverse position cuts out all resistance and puts the armature circuit directly across line voltage.
There are more elaborate drum controllers with more positions and a greater control of speed. However, they all use practically the same circuit arrangement
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