Why back EMF is used in DC motor?

Back emf is very significant in the working of a dc motor. The presence of back emf makes the d.c. motor a self-regulating machine i.e., it makes the motor to draw as much armature current as is just sufficient to develop the torque required by the load. … Thus, the driving torque increases as the motor slows down.

Why is back emf produced 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 the purpose of back emf?

In motor control and robotics, back-EMF often refers most specifically to actually using the voltage generated by a spinning motor to infer the speed of the motor’s rotation, for use in better controlling the motor in specific ways.

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What will happen if the back emf of DC motor?

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. If supplying unit didn’t trip down by this time, excess current in armature may heat up the armature.

What is the difference between emf and back EMF?

EMF (or Electro Motive Force) is the voltage applied to the motor from an external power supply. Back EMF is the voltage produced within the motor windings which is opposite polarity but smaller than the applied voltage. Think of a motor as also being a generator.

Is back EMF good or bad?

It’s kind of a good thing. Back EMF keeps current from going nuts. Pure resistance is kept low to keep heating down. After you’ve done that, you are relying on back EMF to keep your breakers un-popped and power components un-cratered.

Is back emf AC or DC?

Back EMF can have either a sinusoidal (AC) or a trapezoidal (DC) waveform. The shape of the back EMF is important, as it determines the type of drive current and commutation method that should be used for the motor. Circuit diagram and example taken from New South Wales, Department of Education and Training, 2007.

Why back emf is less than applied voltage?

Back EMF is less than the applied voltage because of the resistance of the armature winding. In the above circuit the Back emf can be written as, Therefore, Now in the above equation if the value of current is negative then back emf can be higher than the applied voltage, which is the case for the generators.

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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 should happen if there is no back emf?

If there is no back end then large current flows in starting of motors because initial speed is zero and back emf is zero thus winding gets damaged for this purpose only we use starters for all motors. motor will not start. when the motor runs,there has to be back emf.

What happens if motor back emf is 0 no current flows?

So, if back emf is zero that means which tells us that either speed of the motor or field flux or both are zero. In other words, the motor is standstill because field flux is required for creating torque for rotation. So, if E=0, the supplied voltage equals to voltage drop against armature resistance.

What will happen to a DC motor if its back emf is equal to the supply voltage?

As the back emf depends on the current their value also decreases. The magnitude of the back EMF is nearly equal to the supply voltage. If the sudden load is applied to the motor, the motor becomes slow down. As the speed of the motor decreases, the magnitude of their back emf also falls down.

Why is it called back emf?

In motors, the induced emf is often reffered to as the back emf. This is because it opposes the emf input to the motor.

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What is back emf and generated emf?

The back emf is represented as a variable emf that opposes the emf driving the motor. Back emf is zero when the motor is not turning and increases proportionally to the motor’s angular velocity. drop produced in feeder lines by the large current drawn by the motor. until the back emf is nearly equal to the driving emf.

What is back emf constant?

back electromotive force constant (=back EMF constant)

Back electromotive force is the voltage generated at both ends of a winding due to changes in flux linkage in a shaft motor operation. Since the back electromotive force is proportional to the moving speed, it is a constant. The unit is [V/m/s].