To avoid this problem, take the effect of back-EMF into consideration in system design. Motors do have a blowback voltage, a back-EMF that is usually addressed by adding a reverse-biased fast diode, sometimes in addition to a capacitor, across the motor’s supply wires.
What are the factors covering the back emf of DC motor?
In motor design, back EMF is influenced by the number of turns in the stator windings and by the magnetic field. Motors are designed with a back EMF constant that allows the motor to draw the rated current and deliver the rated torque when running at the rated speed.
What does back emf depend on?
The back EMF depends, of course, on the speed of the motor — the change in magnetic flux that generates it increases with motor speed — so that as the motor begins to turn, the back EMF grows until the motor has reached its maximum speed, at which point the back EMF stays at its maximum value.
What is back emf in a DC motor?
When the armature of the DC motor rotates under the influence of driving torque, the armature of the conductors moves through a magnetic field inducing an emf in them. The induced emf is in the opposite direction to the applied voltage and is known as the back emf.
What is back emf equation?
The back emf is calculated based on the difference between the supplied voltage and the loss from the current through the resistance. The power from each device is calculated from one of the power formulas based on the given information. The back emf is ϵi=ϵS−I(Rf+REa)=120V−(10A)(2.0Ω)=100V.
What is the formula for back emf in dc motor?
As the armature rotates, a voltage is generated in its coils. In the case of a generator, the emf of rotation is called the Generated emf or Armature emf and is denoted as Er = Eg. In the case of a motor, the emf of rotation is known as Back emf or Counter emf and represented as Er = Eb.
What will happen if the back emf of a DC motor vanishes suddenly?
Explanation: If back emf vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. … So, with the increase in speed, the back emf also increases. Therefore, armature current is also decreased, in case of series motor, armature current is equal to the line or load current.
What will happen if the back emf in the motor absent?
If back emf of a dc motor vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. As the back emf vanishes zero, the whole supply voltage appears across armature and heavy current flows.
What is the advantage of back emf?
IMPORTANCE OF BACK EMF
A very important advantage of back emf is that it makes the DC Motor to draw only as much as armature current which is just sufficient to develop the torque required by the load. Suppose if the motor is running at no load, it means that speed of the motor will be more.
What factors limit the size of the back emf?
The magnitude of the back emf induced in a coil is directly proportional to the rate of change of flux. As the rate of change of flux depend upon the speed of the motor, therefore by increasing the speed of the motor will increase the back emf and decreasing its speed will decrease the back emf.
Why starters are required in a DC motor?
Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.
Under which condition is the back emf in an electric motor at its maximum value?
Under which condition is the back emf in an electric motor at its maximum value? Motor speed is at maximum.