What Causes Counter Emf In A Dc Motor?

When the armature of a DC motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence emf is induced in them as in a generator. The induced emf acts in opposite direction to the applied voltage V (Lenz’s law) and is known as Back EMF or Counter EMF (Eb).

What causes counter 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 causes 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.

How is the counter electromotive force generated in motor?

When the armature in a motor rotates in a magnetic field, a voltage is induced in its windings. This voltage is called the back or counter emf and is opposite in direction to the voltage applied to the motor from the external source. Counter emf opposes the current, which causes the armature to rotate.

What motor characteristics is affected by counter EMF?

When the field current is increased, the field flux is increased. More counter EMF is developed, which opposes the armature current. The armature current then decreases, and the motor slows down. When the voltage applied to the armature is decreased, the armature current is decreased, and the motor again slows down.

What is counter electromotive force in a motor?

counter electromotive force. The emf that opposes the flow of current. Just as the windings of a generator produce voltage, the rotor in a motor produces voltage that is counter or opposed to the supply voltage. This counter emf creates additional resistance that must be overcome by the supply voltage.

How do you stop the back emf in 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.

How do you stop back emf?

When the switch opens fly wheel current produces a back EMF in the opposite polarity and so the diode will conduct. The diode does a very good job of suppressing the back EMF and clamps the voltage to around a one volt or so. This is quite suitable for small solenoids like those found in strikes.

What determines the magnitude and polarity of the counter EMF in a DC motor?

The magnitude of the counter EMF is dependent on the magnetic field strength and the speed of the rotation of the armature. When the DC motor is initially turned on, there is no counter EMF and the armature starts to rotate. The counter EMF increases with the rotation.

What will happen if the back emf of a DC motor vanishes suddenly?

Detailed Solution. 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.

Does back emf occur in AC motors?

YES! Stator winding is nothing but a coil in essence. When AC power is applied across any coil of wire, a back emf is produced within the coil which opposes the applied voltage and limits the applied current which causes the applied current to lag behind the applied voltage.

What is the relationship between a conductor and counter EMF?

What is the relationship between a conductor and counter emf? It is the opposition to the changes in current flow.

What factors limit the size of back EMF?

Answer: 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 factor determines the speed regulation of a DC motor?

The speed regulation of a DC motor is proportional to the resistance of the armature. The lower the armature resistance the better the speed regulation. The reason for this is that armature current determines the torque produced by motor if field excitation remains constant.

How do you counter a magnetic field?

The simple answer is that it is not possible to totally ‘block’ a magnetic field. The essence of a magnet, as determined by nature, is that magnetic field lines must terminate on the opposite pole and, therefore, there is no way to stop them. Our own Earth’s magnetic field is a perfect example.

What diode is used to remove back EMF?

Protection or snubber diodes are installed across the motor terminals, opposing the supply voltage. Thus, when the motor turns off, the diode presents a short circuit to the back EMF, allowing it to dissipate safely.

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 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 the stator in a DC motor?

The stator is the stationary part of a motor, while the armature rotates. In a DC motor, the stator provides a rotating magnetic field that drives the armature to rotate.

What does a commutator do in a DC motor?

On DC and most AC motors the purpose of the commutator is to insure that the current flowing through the rotor windings is always in the same direction, and the proper coil on the rotor is energized in respect to the field coils.

What is field winding in DC motor?

field winding in Electrical Engineering
A field winding is the insulated current-carrying coils on a field magnet that produce the magnetic field needed to excite a generator or motor. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding.