The back emf opposes the supply voltage. The supply voltage induces the current in the coil which rotates the armature. The electrical work required by the motor for causing the current against the back emf is converted into mechanical energy. And that energy is induced in the armature of the motor.
What is meant by back emf in dc motor?
Back EMF is the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates. When the speed varies, the winding characteristics may fluctuate, resulting in variation of back EMF.
What is the back EMF of the motor?
Back emf is the generator output of a motor, and so it is proportional to the motor’s angular velocity ω. It is zero when the motor is first turned on, meaning that the coil receives the full driving voltage and the motor draws maximum current when it is on but not turning.
What is back EMF in DC motor and its significance?
The significance of Back EMF
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.
What is meant by back EMF?
Counter-electromotive force (counter EMF, CEMF), also known as back electromotive force (back EMF), is the electromotive force or “voltage” that opposes the change in current which induced it. CEMF is the EMF caused by magnetic induction (see Faraday’s law of induction, electromagnetic induction, Lenz’s law).
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.
What will happen if the back EMF of dc motor vanishes?
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. 3.
Is back EMF good or bad?
Back emf is a measure of energy conversion from electrical to mechanical in an electric motor. If you are able to make it zero no energy conversion to mechanical. … Eb is back emf, I armature current and R armature circuit resistance. So if you want energy conversion back emf is good.
How do you prevent back EMF?
Back EMF cannot be prevented but it can be controlled. In suppressing the back EMF the objective is to prevent the very high voltages and dissipate the stored energy in a controlled way.
Why does back EMF occur in an electric motor?
A motor has coils turning inside magnetic fields, and a coil turning inside a magnetic field induces an emf. … This emf, known as the back emf, acts against the applied voltage that’s causing the motor to spin in the first place, and reduces the current flowing through the coils of the motor.
How do you reduce the back EMF of a dc motor?
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 is disadvantage of back EMF starter?
One disadvantage is that no back EMF is generated when the motor is stationary, so startup is affected by operating in open loop. Consequently, the motor can take a short time to settle and run efficiently.
What is DC motor working principle?
The DC motor is the device which converts the direct current into the mechanical work. It works on the principle of Lorentz Law, which states that “the current-carrying conductor placed in a magnetic and electric field experience a force”.
What is the difference between EMF and back EMF?
If an open coil is subjected to a variable magnetic field, at the ends of the coil a potential difference is induced which is called induced emf. If a coil is connected to an emf source and switched on, the rising current will produced an variable magnetic field which in turn produces an emf. It is called back emf.
What is back EMF and write its formula?
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.