What is meant by back emf?
Counter-electromotive force (counter EMF, CEMF), also known as back electromotive force (back EMF), is the electromotive force (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).
What is the formula for back emf of a DC motor?
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.
How back emf controls the speed of a DC motor?
Back EMF always acts to reduce the changing magnetic field through the coils. It does so by generating a voltage which opposes the supply voltage, thus reducing the current. In ideal DC motor where R=0 and L=0, and RPM is constant with no load, back EMF will be exactly the same as the supply voltage.
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.
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.
What is back emf in relay?
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 emf in a DC motor?
When armature of dc motor rotates, the armature conductors move through the magnetic field, emf is induced in them. The induced emf acts in opposite direction to applied voltage. This voltage is known as back emf.
Why back emf is used in 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.
Is back emf suddenly disappears in a DC motor?
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.
How back emf is generated?
When the coil of a motor is turned, magnetic flux changes, and an emf (consistent with Faraday’s law of induction) is induced. Lenz’s law tells us the emf opposes any change, so that the input emf that powers the motor will be opposed by the motor’s self-generated emf, called the back emf of the motor.
Why is the DC motor called back EMF?
The electromotive force or EMF produce in the armature winding of a dc motor in opposite direction to the applied voltage is called Back EMF. In fact, as the direction of Back EMF is opposite to the applied voltage and gives back the energy towards the energy source, that’s why it is called back emf.
How is mechanical energy induced in a DC motor?
The mechanical energy induced in the motor is the product of the back emf and the armature current, i.e., E b I a. 2. The back emf makes the DC motor self-regulating machine, i.e., the back emf develops the armature current according to the need of the motor.
What are the properties of the back EMF?
1 Characteristics and Properties of Back EMF. Back EMF always has the opposite direction to the Supplied Voltage. Back EMF always lower than the supply voltage. 2 Equation and Formula of Back EMF 3 Importance and Significance of Back EMF. The main importance or significance of Back EMF is, it makes the DC motor a Self Regulating Machine.
What is the relation between back EMF and armature current?
The relation between the main supply, back emf and armature current is given as E b = V – I a R a. 1. The back emf opposes the supply voltage.