# What is the back EMF of the 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.

In respect to this, how does back EMF occur?

Counter-electromotive force. The term back electromotive force is also commonly used to refer to the voltage that occurs in electric motors where there is relative motion between the armature and the magnetic field produced by the motor’s field coils, thus also acting as a generator while running as a motor.

What is EMF how it is produced?

Current produced by the relative motion of coil or magnet is called induced current, set up by an induced electromotive force or EMF. The production of EMF in a coil is called the phenomenon of ELECTROMAGNETIC INDUCTION.

What is the back EMF of a dc motor?

When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The induced e.m.f. acts in opposite direction to the applied voltage V (Lenz’s law) and in known as back or counter e.m.f.

## What is meant by slip in an induction motor?

Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’.

## What type of starter is used for DC shunt motor?

A 3 point starter is used for starting a DC shunt motor. A 4 point starter is used for starting a DC compound wound motor.

## Why do we need a starter in DC motor?

In other words, the starter offers resistance to armature current during starting of dc motor only. As the speed of armature/motor build up, armature induced emf also starts building thus reducing the role resistance offered by the starter, hence requiring it to gradually reduce as the motor picks up full speed.

## Why do we need a starter?

In dc motors the armature is generally designed to have the least resistance possible. So when starting a dc motor starter is connectedsuch that it limits the current value by being in series with armature and later seperates from the circuit. But by then back emf develops in the armature.

## Why is the current drawn by a DC motor so high at starting?

The starting current is high as there is no back EMF or counter EMF present in the armature circuit because at starting counter EMF is zero. It’s armature has very less resistance due to this it need more current at starting time. Hence DC starters are used to limit the starting current of motor.

## Why is starting current high in a motor?

An induction motor during start behaves like a short circuited transformer. Now, when supply is given to the stator windings, it draws high current at constant voltage as the windings are short circuited. This high current through the stator turns generate magnetic field which links with the rotor conductors.

## How does a DC motor start?

Starting of DC Motors. At the moment a DC motor is started the armature is stationary and there is no counter EMF being generated. The only component to limit starting current is the armature resistance, which, in most DC motors is a very low value (approximately one ohm or less), as shown in Equation (6-9).

## What is the difference between AC and DC motors?

D.C wound field motors are constructed with brushes and a commutator, which add to the maintenance, limit the speed and usually reduce the life expectancy of brushed D.C. motors. A.C. induction motors do not use brushes; they are very rugged and have long life expectancies. The final basic difference is speed control.

## How does a DC motor work?

How does a DC Motor work? The DC motor is a machine that transforms electric energy into mechanical energy in form of rotation. Its movement is produced by the physical behavior of electromagnetism. DC motors have inductors inside, which produce the magnetic field used to generate movement.

## What are the main components of a DC motor?

Every DC motor has six basic parts — axle, rotor (a.k.a., armature), stator, commutator, field magnet(s), and brushes. In most common DC motors (and all that BEAMers will see), the external magnetic field is produced by high-strength permanent magnets1.

## Where DC motor is used?

The series DC motor is an industry workhorse for both high and low power, fixed and variable speed electric drives. Applications range from cheap toys to automotive applications. They are inexpensive to manufacture and are used in variable speed household appliances such as sewing machines and power tools.

## What are the applications of DC motors?

The various applications of DC shunt motor are in Lathe Machines, Centrifugal Pumps, Fans, Blowers, Conveyors, Lifts, Weaving Machine, Spinning machines, etc. The compound motors are used where higher starting torque and fairly constant speed is required.

## Why DC shunt motor is started on no load?

Motor armature current is decided by the load. On less load or no load, the armature current drawn by the motor is very small. and on no load as I is small hence flux produced is also very small. This is the reason why series motor should never be started on light loads or no load conditions.

## What will happen if the field of DC shunt motor is opened?

In d.c shunt motor if field winding supply is removed the motor back emf will drop to zero, hence the armature will draw more current to make up the emf.this results in blowing up of fuse. In dc series motor the motor will go to infinite speed (theoretically) as flux is inversely proportional to the speed

## What is no load speed of a motor?

Motor characteristics are frequently given as two points on this graph: The stall torque, , represents the point on the graph at which the torque is a maximum, but the shaft is not rotating. The no load speed, , is the maximum output speed of the motor (when no torque is applied to the output shaft).

## What is a no load for motors?

It just means that the motor has been started and running without any mechanical load being put on its shaft. It will draw a small amount of current from the mains to supply the small electrical (copper and core) and mechanical ( friction and windage ) losses.

## What is a no load speed?

A cordless screwdriver’s maximum speed will be presented as a number followed by ‘RPM’. The higher the number, the higher the tool’s maximum no-load speed. The no-load speed is the maximum speed a cordless screwdriver can reach without a load. (When it’s not driving screws or drilling holes).

## Is more horsepower better?

It measures twisting force. The more torque a car has, the better it can accelerate from a stop and the more strength it has for towing. The engines in high-performance cars are tuned so that the horsepower and torque ratings complement each other and provide a well-balanced driving experience.

## What is the effect of back EMF in DC motor?

When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The induced e.m.f. acts in opposite direction to the applied voltage V (Lenz’s law) and in known as back or counter e.m.f.

## How the EMF is produced?

When a magnet is moved into a coil of wire, changing the magnetic field and magnetic flux through the coil, a voltage will be generated in the coil according to Faraday’s Law. The polarity of the induced emf is such that it produces a current whose magnetic field opposes the change that produces it.

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