charging systems and controlls Flashcards
purpose of a charging system
to provide the electrical current required to operate the system and charge the battery when necessary
the charging system converts
mechanical energy into electrical
12 volt open circuit voltage
12.6 v
24 volt open circuit voltage
25.2 v
alternator must
produce enough electric current to operate all of the units electrical loads
battery group must
assist in the supply of electrical current when idling and when electrical accessory load is high
voltage regulator
when battery voltage drops to a set level the voltage regulator (electric switch) turns on the alternator and current is produced
regulator may start and stop a alternator field circuit as many as
6000 times per second
maximum voltage setting for a 24 volt system
29.6 volts
maximum voltage setting for 12 volt system
14.8 volts
if charging exceeds the maximum voltage setting for the system
damage to the battery group or other electrical components could be caused
alternator induces voltage by
rotating a magnetic field (rotor) inside a fixed conductor (stator)
alternators can be belt driven and
gear or coupler driven
the greatest induced voltage occurs when
the rotors magnetic field is at 90 degrees to the stator
the field circuit
delivers current to the alternators field windings creating a magnetic field inside the alternator
output circuit
sends electrical current to the battery group and electrical loads
alternating current
switches from positive to negative flow in a circuit moving one direction then the other
AC voltage is also called
sine wave voltage
single phase voltage
caused by one revolution of the rotor across one conductor
because batteries can only carry DC current AC current must be
rectified
alternator brushes
carbon brushes slide on the contact surface of the slip rings only carry small current required to induce the magnetic field in the rotor core
why is alternator rotation considered bi directional
because because the stators direction changes multiple times every rotation is dose not matter witch way it is rotated
methods for controlling heat in an alternator
heat sinks and cooling fans
Heat sink
finned block of aluminum that absorbs and moves heat away from sensitive components
cooling fans
pulls cool air from the back of the alternator past internal components and out the front
what is a limiting factor in maximum current output for an alternator
the design of the stator
Rotor
carries the alternators magnetic field
is a coil of wire surrounded by two pole pieces
pole pieces
are interfacing fingers that will take on either north or south pole when magnitized
typical field circuit range is
2-10 amps
stator
is made up of three conductors wound onto a cylindrical laminated iron core
why do you laminate the iron stator core
to reduce heat build up from eddy currents in the core material
eddy currents
are localized circular current flows developed in the confines of the stator core by alternating electromagnetic fields
eddy currents change the mechanical input energy into unwanted heat
three phase current
is three evenly spaced overlapping single phase ac voltage waves
two types of stators
wye and delta
delta type stator
stator windings are connected end to end
shaped like a triangle
used in alternators with high current output demands
diodes
act as a one way electrical check valve
used in the rectification of ac voltage
half wave rectification
only half of a ac singe wave is allowed through a diode creating pulsating dc current
alternator housing
made of two piece cast aluminium because it is lightweight transfers heat well and is nonmagnetic
drive end housing
holds the bearing for the end of the rotor shaft where the drive pulley is mounted
rear housing
holds the diodes heat sinks brushes and electrical terminal connections also holds the bearing for the slip ring end of the rotor shaft
alternator terminals
because the alternator is bolted directly to the engine it becomes part of the ground circuit
any positive diodes or terminals that must be insulated must be carefully insulated form the alternator case
alternator capacitors
are installed between the positive diodes output terminal and the negative diodes ground circuit case mount
protects the electronic components from transient voltage spikes and reduces radio frequency interference
how are capacitors rated
by there capacitance measured in farads
what is a diode bridge
a group of negative or positive diodes connected into a heat sink
positive diodes need to be insulated from the alternators ground circuit negative diodes don’t
filter capacitor
used to smooth out ac voltage fluctuations and protect the diodes in the system from to much reverse bias voltage
also
RFI
radio frequency interference
how is a wye type stator connected
one of each ends of the stator windings is connected to a junction the free end is then connected to a positive and a negative diode the stator
used when a high voltage output is needed at low alternator speeds
how are delta type stators connected
by joining each stator winding end to end and then connected to a positive and negative diode
produce more current output total then why stator but will have less voltage total at low speeds
maximum allowable ac ripple from 12 and 24 volt systems
12 volt = .5 volts
24 volt = 1 volts
residual magnetism
is the magnetism left in the electromagnetic iron core after the vehicle is shut off
some times the core needs to be excited by the batteries to produce a voltage in the stator windings
full fielded condition of an alternator
when the alternator is at maximum current flow
alternator will be naturally governed by the counter electromotive force that happens in the stator windings
Brushless alternators
the field winding will not rotate with the rotor
it is held stationary while the rotor rotates around it in close proximity to keep the magnetic field strong
A-circuit construction
voltage regulator process the current flow after it passes through the rotor windings
B-circuit construction
voltage regulator processes the current flow before it pass through the rotor windings
two types of cooling classes for alternators
open or closed
open cooling to an alternator
has holes and a fan allowing passing air to cool internal alternator parts
closed alternator cooling
have long service life and are internally cooled bye engine oil or air
R or STA auxiliary terminals can be used for
running a tachometer, hour meter or relay
also can be used to excite the field coil if residual magnetism has become weak in rotor
Charging system indicators
ammeter
voltmeter
indicator lamp
ammeter indicator
measures current flow in or out of the battery group
voltmeter indicator
measures indicated voltage of the alternator or the battery group which ever is greater
indicator lamp
will illuminate if there is an unequal voltage on either side
