How can you control the speed of a DC motor by varying the resistance in the armature circuit?

How can you control the speed of a DC motor by varying the resistance in the armature circuit?

Speed Control of D.C. Motors

• Resistance variation in the armature circuit: This method is called armature resistance control or Rheostat control.
• Variation of field flux Ф This method is called field flux control.
• Variation of the applied voltage. This method is also called armature voltage control.

What are the factors that controls motor speed?

The above equation shows that the speed depends upon the supply voltage V, the armature circuit resistance Ra, and the field flux Ф, which is produced by the field current. In practice, the variation of these three factors is used for speed control.

How is motor speed measured?

A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common.

How speed varies with field current supply voltage and armature current?

Speed of a dc motor is directly proportional to the back emf Eb and Eb = V – IaRa. That means, when supply voltage V and the armature resistance Ra are kept constant, then the speed is directly proportional to armature current Ia. Greater the resistance in series with the armature, greater the decrease in speed.

What is relation between armature voltage and speed?

In the armature control method, the speed of the DC motor is directly proportional to the back emf (Eb) and Eb = V- IaRa. When supply voltage (V) and armature resistance Ra are kept constant, the Speed is directly proportional to armature current (Ia).

How to control the speed of DC series motor?

Armature Voltage Control Method for DC Series Motor. In this method, the speed is controlled by varying the armature voltage (supply voltage). A separate variable voltage source is required in this method. The speed of a motor is proportional to the supply voltage. So, if the voltage increases, the speed of the motor will increase and vice versa.

How can the output voltage of a DC motor be varied?

The output voltage of generator G can be varied from zero to its maximum value by means of its field regulator and, hence, the armature voltage of the motor M 2 is varied very smoothly. Hence, very smooth speed control of the dc motor can be obtained by this method.

How does resistance affect the speed of a DC motor?

An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed. This method of speed control is independent of load on the motor. Power wasted in controlling resistance is very less as field current is a small value. This method of speed control is also used in DC compound motor.

What are the speed control methods for a DC shunt motor?

The classification of speed control methods for a DC shunt motor are similar to those of a DC series motor. These two methods are: Armature controlled DC shunt motor can be performed in two ways: In armature resistance control a variable resistance is added to the armature circuit.