Download Electrical Component Concepts

Electrical
•Electricity
•Fuses
•Relays
•Solenoids
•Electrical Testing
•Wiring Harnesses
•Testing
•Voltage Drop Testing
•Test Procedures
•Cables/Connections
•Glow Plugs
What is Electricity?
• The flow of electrons from atom to atom in a
conductor
• Electricity is based on a theory- an “unseen”
force because the energy itself cannot be
seen, heard, touched, or smelled
Fuses- devices used to protect the electrical
circuit from too much current flow
•A fuse is designed to open the circuit when the
current reaches a predetermined level.
•Fuses are rated in Amps
•Do not install a fuse larger than is designed for
the circuit
Why Use Relays?
•To direct electricity to a high current device like a
starter motor, with the use of a light duty switch
(key switch)
•To control devices
-A relay is a switch that changes states when voltage
is applied to its input. The input connects to an electric
coil. When voltage is replaced across the input, the coil
magnetizes and moves a switch contact.
Why Use Relays?
•Relay we use has a single switch that is normally open
(N.O.)- refers to the effect of the switch in its normal
(non-energized state)
87A
Electric symbol we use for these
relays - the symbol shows the coil
and switch
87
30
86
85
-When the coil is not energized a spring keeps the switch
held open or OFF. When the coil is energized the magnetic
field pulls the switch against the normally open contact
thereby closing the switch.
Starter motor solenoid or magnetic switch
– Consists of a contact plate, plunger, plunger shaft,
pull-in coil, hold in coil and return spring
-When power is applied to coil terminal (key turned to start), current
flows through pull in and hold in coils. Magnetic field pulls in plunger
(the end of plunger has a contact disc). Disc makes contact with the
two main contacts and an R terminal contact. Battery is connected to
one main contact and the starter motor is connected to the other.
Current flows between the battery and starter motor. Current also
bypasses the pull in coil. The hold in coil continues to keep the solenoid
energized until the key switch is opened. At that instant current no longer
flows through the hold in coil and the contact disc is spring returned and
starter motor quits turning.
Solenoid- a coil of wire
When voltage is placed across ends of coil, coil
magnetizes (magnetism moves a plunger)
Cut away view of coil commonly found on hydraulic
control valves
–Solenoids often take the place of what use to be done by mechanical
linkages, levers and switches.
-Common uses for solenoids are to control mechanical, hydraulic and
electric circuits.
Sensors
•Sensors (referred to as senders) - devices that respond
to a physical “stimulus”
•Variable Resistive Sensors - as physical property
changes, resistance of sensor changes
•Variable Capacitance Sensors - (engine oil pressure and
hydraulic oil charge pressure)
–three wires to these sensors: ground lead, supply voltage lead
and sensor signal
–Variable Capacitance sensors- have a circuit built into them.
The circuit converts the capacitance to an output voltage proportional
to the pressure. As the pressure increases the voltage increases.
Sensors
Switch sensors (air filter and hydraulic filter)
–close or open when the physical property reaches
predetermined level
Testing
•Harnesses - Suspected defect in a wire
–test for continuity with an ohm meter
–after checking for continuity, check for a short to nearby
pins, battery ground and battery positive
•Switches - Test leads on correct pins
–With wires disconnected from the switch, connect ohm
meter across the switch
–Switch can often be tested with a voltmeter in a live circuit
-With the switch open you should read infinite ohms. With the switch
closed you should read zero ohms. Anything other than these
readings indicates a faulty switch.
Testing
•Relays - Test activation signal
–May be able to test for activation signal by listening to
the relay
–Test switch output
–same test for any other switch
–activate the relay and check that the switch functions
properly
-Activation Signal- When activated and or deactivated, many relays make a
clicking sound. If the clicking sound is present, you can generally assume that
the activation signal is present. A more positive method is to check for ground
and the correct activation signal at the relay using a volt meter. If you do not
have the activation signal, the relay coil was shorted and should be replaced.
If you do not have the activation signal, the cause for this must be found.
Testing
Relays – Quick Testing Tips
•Replace relay with a known good relay
• quick and effective
•Remove relay and put a jumper across correct pins to
simulate a closed switch
–if output circuit functions, the circuit is ok
Testing
•Modules / Controllers
•First, check for correct ground and power to module
•If a known good module is available, replacement is
the best test
•Observe symptoms
•Often controllers are expensive
–casual controller replacement is not recommended
-Because modules often are complex internally and perform many
functions, it can be difficult to determine if a problem exists.
Voltage Drop Testing
•Voltage drop- the difference in voltage potential when
measured across a circuit or component creating resistance
-Voltage Drop- “Resistance decreases the amount of voltage available.”
•Resistance- an opposing force, created by a circuit or
component, to the flow of electrical current
-Resistance- “There is a small amount of natural resistance when voltage
flow through wires, switches, grounds or connections. The resistance
increases beyond acceptable limits if corrosion develops, fittings become
loose or wires fray. Resistance increases each time something, such as a
wire, a switch, connections, or the ground are added to the circuit.”
What Else Should be Tested
–Each wire, ground, connector, switch, solenoid and the
complete circuit should be tested
–Each connection point is a potential source of increased
resistance