Circuit Protection Protective Devices – terminate current flow in a circuit. Located in series within a circuit Excessive current flow results from a decrease in circuit resistance. Excessive current flow can damage components and wiring. Shorts – Undesirable, low resistance path for current to flow.
19
Embed
Circuit Protection Protective Devices – terminate current flow in a circuit. Located in series within a circuit Excessive current flow results from.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Circuit ProtectionCircuit Protection Protective Devices – terminate current flow in
a circuit. Located in series within a circuit Excessive current flow results from a
decrease in circuit resistance. Excessive current flow can damage
components and wiring. Shorts – Undesirable, low resistance path for
current to flow.
Fusible linksFusible links Special section of wire
designed to melt(open) when current flow exceeds it’s rating
Fusible link usually 4 wire sizes smaller than the circuit it protects
Must be replaced with wire of same rating
Located near starter or Pos. battery terminal
FusesFuses Glass Cartridge
Minifuse
Autofuse
Maxifuse
Fuse RatingsFuse Ratings
Element within the fuse melts if current exceeds its rating
See figure 3-3 on page 53
Circuit BreakersCircuit Breakers Protects circuits that
are prone to overloading
Some reset themselves, others must be manually reset
Solid state design – no moving or replaceable parts
Positive temperature coefficient – resistance increases as current increases,
ECB resets when it cools Commonly found in power window motors and
power door lock actuators
SwitchesSwitches
Control current flow through a circuit
Normally open – no current flow when switch is at rest
Normally closed – current flow when switch is at rest
SwitchesSwitches
SPST –Single pole single throwPole - number of input circuits
Throw – number of output circuitsSPDT – Single pole double throwGanged switch – several contacts move
together, affect several circuitsMercury switch – detects motion
RelaysRelays Device that
uses low current to control a high current circuit
Electro-magnetic switch
SolenoidsSolenoids Electromechanical device that performs work
Electromagnet that moves an iron core one way, an internal spring resets core
Some solenoids require reverse polarity to reset core
Variable ResistorsVariable Resistors Vary input voltage or current to an output device Stepped resistor – several fixed resistor values Rheostats – two wire regulator of electrical
current – Resistance value changes Potentiometer – three wire resistor that acts as a
voltage divider, produces a continuously variable output signal proportional to a mechanical position
Electronic ComponentsElectronic Components
DiodesDiodes One way electrical valve Zener Diode – Allows voltage to pass in the
opposite direction when voltage exceeds a certain limit
LED – Light-Emitting DiodeLED – Light-Emitting Diode Forward biased LED
that emits light No filament, will last
a very long time Used in IP clusters
and Tail lights Requires very little
current to operate
Clamping DiodeClamping Diode
Used to suppress voltage spikes Wired in parallel with a electromagnetic coil –
A/C clutch Connected to the circuit in reverse bias
TransistorTransistor
Regulates current or voltage and acts as a switch or gate for electronic signals
Solid state switching device
PhototransistorsPhototransistors
A semiconductor device which conducts a current proportional to the light incident on it. It behaves like a normal transistor, except that it has a transparent top to its case and a small current is produced by photons generating electron-hole pairs in the base (photoelectric effect). This small current is amplified by the transistor action
Detects available light, used in automatic lighting systems
PhototransistorPhototransistor
Used on GM power sliding doors to monitor door movement and location
Circuit DefectsCircuit Defects Open – A break in circuit continuity, stops
current flow Short – Current bypasses the normal circuit path
Short to groundShort to powerShort to another circuit
High Resistance – unwanted opposition to current flow