Q.. What is the function of charging system? Explain.
The function of charging system,
*The automobile requires a charging system to keep the battery charged and to produce electricity.
*While the engine is in operation, the charging system produces electricity to
(i) Re-charge the battery and
(ii) To supply required amount of electricity to the electrical components
*It is necessary for the battery to be fully charged always so that it supplies the necessary amount of electricity to cach
of the electrical components at the required time.
Thus the charging system accomplishes the following functions,
*To handle the ignition, load of lights, radio and other electrical and electronic equipment especially while the engine is running
*To put back the current into the battery (current used to start the engine).
Some of the requirements of a charging system when vehicle is running are,
*To have highest power to weight ratio.
*To be quiet and reliable.
*To require least maintenance.
*Under all conditions it should supply the constant voltage.
*Under all conditions it should supply the current required for charging of battery.
The charging system components are
* Regulator * Relay
* Armature (or) indicating lamp
Q..Write short note on the cut out relay as used in the battery generator circuit.
Explain the working of a cut out relay as
used in the charging circuit.
The D.C generator is connected to the battery through
a cut out relay and an ammeter. The cut out relay closes the
circuit between the generator and the battery when the gen
crator is producing current. It also opens the circuit when the
generator stops or slows down, so that the battery cannot
discharge back through the generator.
This reverse direction of flow of current in the series
winding causes the magnetic field to reverse Thus, the mag.
netic fields of the winding remains no longer and is so weak
and that it cannot hold the armature down. The spring ten
sion pulls the cut out contact points. This opens the circuit
between the generator and the battery
Q.. Battery is the heart of electrical system in an automobile. Explain briefly.
Battery is one of the most important component of
electrical system. In reality, battery is considered as the “heart
of electrical system” of a vehicle because it supplies current
for cranking rotor and the ignition when the engine is being
Functions of a Battery
1. To supply current to start motor and ignition system before the start of engine.
2. It supplies electricity for operating various electrical
devices such as Lights, A/C, Music system etc., when
the generator is not handling the load.
3.It acts as secondary source of electrical energy when
the vehicle is not operating of the generator speed is
inadequate to meet the full load requirement
Battery is a device which converts chemical energy to
electrical energy. The duration or life span of the battery
depends upon the quality and quantity of chemicals used. It
stores the electrical energy, which can be used whenever
required. Without a battery, an engine cannot be started with
the starting motor.
Q.. Discuss the construction and working of starter
motor for automobiles.
Construction of a Starter Motor
*Its construction is similar to the D.C generator con
structure, except that the generator is shunt wound
and it is series wound.
*The main components of the starter motor are the body.
the commutator, the armature and the field windings.
*Most automobile starting motor have four brushes
and four field poles.
*Brushes are held against the commutator with the help
*The armature consists of heavy duty copper windings
and a segmented copper commutator.
*Wave winding technique is used for starter motor as
it gives most appropriate torque and speed character
is it for a four-pole system.
*At the end of the armature shaft there is some form of
drive mechanism by which the motor starts the engine.
*For light and medium cars, starter motor of stalling
torque 10-30 Nm and for larger cars the starting torque
required are 50-ISO Nm. *The starter motor is connected to the battery where it
draws the current for its operation.
*The amount of current drawn for starting may be 500
*Hence, motor winding of copper cable (Standard) of
large diameter is used to
*The cable of shortest possible length is employed to
keep the resistance in the circuit low.
*Also the battery voltage falls by considerable amount
due to very heavy current discharge during starting.
*Unless battery of adequate capacity is provided and
maintained in good condition, the battery voltage drop
will not allow the torque to be developed.
Working of Starter Motor
*The starter motor is driven by means of the current taken (or) provided by the battery.
*It is mounted on the side of the engine.
*The motor must be powerful in order to turn the engine at a speed such that the carburettor will give a suitable air-fuel
*It should be capable of exerting a heavy torque at low speeds and when starting, for this purpose the starter motor, is
series wound. *In a series motor, the field coils are connected in series with the armature windings for the purpose of equalizing the field
and armature currents. Now-a-days starter motors are also series shunt wound.
*The advantage of this type of system is that we can get lower internal resistance. *Due to this motor output for a given current consumption is higher in comparison with a series wound motor.