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Automotive Electrical SystemsAutomotive Electrical Systems

R. BortignonR. Bortignon

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Electrical CircuitsElectrical Circuits

Contain 4 main parts…Contain 4 main parts…

1. Power source1. Power source batterybattery alternatoralternator

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LoadLoad2. The2. The loadload in a circuit is the part that does thein a circuit is the part that does the workwork

load will always have some resistanceload will always have some resistance this resistance can be measuredthis resistance can be measured

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ControlControl3. The 3. The controlcontrol is what turns the load on or off… is what turns the load on or off… opens & closes the circuitopens & closes the circuit may be installed on the ground side or the power side of circuitmay be installed on the ground side or the power side of circuit

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PathPath

4. The path are the 4. The path are the wireswires that connect the battery & alternator to the control and that connect the battery & alternator to the control and load devices in a circuitload devices in a circuit frame/body of the vehicle is a path for the ground circuitframe/body of the vehicle is a path for the ground circuit

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Circuit ProtectionCircuit Protection

• to protect the vehicle’s electrical system from excessive current flow, fuses are usedto protect the vehicle’s electrical system from excessive current flow, fuses are used

fuses open the circuit if current (amperage) levels exceed a predetermined levelfuses open the circuit if current (amperage) levels exceed a predetermined level

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Types of FusesTypes of Fuses

• cartridge fusescartridge fuses

• blade type fusesblade type fuses mini sizemini size standard sizestandard size maxi sizemaxi size mega fusemega fuse

• ceramic disc fusesceramic disc fuses see info on next slidesee info on next slide

replace fuses with correct amperage rating!!!replace fuses with correct amperage rating!!!

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Positive Temperature Coefficient FusesPositive Temperature Coefficient Fuses

PTC fuse technology utilizes a polymer-based material to protect electrical circuits from excessive PTC fuse technology utilizes a polymer-based material to protect electrical circuits from excessive

current. current.

During normal operation, numerous carbon paths within the polymer allow the device to conduct During normal operation, numerous carbon paths within the polymer allow the device to conduct

electricity. electricity.

As current through the PTC fuse reaches its rated threshold, the polymer material begins to heat As current through the PTC fuse reaches its rated threshold, the polymer material begins to heat

causing the polymer to expand. causing the polymer to expand.

The resulting expansion breaks the carbon chains to reduce the current through the circuit to a small The resulting expansion breaks the carbon chains to reduce the current through the circuit to a small

leakage current. leakage current.

The increased resistance in this resettable fuse works to protect circuitry by limiting potentially The increased resistance in this resettable fuse works to protect circuitry by limiting potentially

damaging current. damaging current.

When the fault (over-current) is removed from the circuit, When the fault (over-current) is removed from the circuit, the PTC fuse will reset itselfthe PTC fuse will reset itself thereby thereby

allowing current to flow through the circuit again.allowing current to flow through the circuit again.

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• many older vehicles use glass cartridge fusesmany older vehicles use glass cartridge fuses

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Fuse Panel LocationsFuse Panel Locations

• can be located…can be located… under left side of instrument panelunder left side of instrument panel in the engine compartmentin the engine compartment many vehicles have fuse panels in many vehicles have fuse panels in both locationsboth locations

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Fusible LinksFusible Links

• special wire that breaks & opens a circuit when overloadedspecial wire that breaks & opens a circuit when overloaded

• insulation bubbles, melts & opens to expose wireinsulation bubbles, melts & opens to expose wire

• usually connected near the battery & feeds the fuse box(es)usually connected near the battery & feeds the fuse box(es)

• must be replaced with correct ratingmust be replaced with correct rating

• not all vehicles use fusible linksnot all vehicles use fusible links

modern vehicles use maxi fuses instead of fusible linksmodern vehicles use maxi fuses instead of fusible links

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Circuit BreakersCircuit Breakers

• some circuits such as power windows & power seats use some circuits such as power windows & power seats use circuit breakerscircuit breakers• circuit breakers reset themselves when current levels are back to normal circuit breakers reset themselves when current levels are back to normal

(do not need to be replaced like fuses)(do not need to be replaced like fuses)