Circuit Protection

1. 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.

2. ELEMENTS OF ELECTRICAL ENGINEERING FIRST YEAR ELECTRICAL -2 • URVI JADAV (13ELEE174) • VAIBHAVI SHAHANE (13ELEE175

3. Fusible 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

4. Fuses • Glass Cartridge • Minifuse • Autofuse • Maxifuse

5. Fuse Ratings • Element within the fuse melts if current exceeds its rating • See figure 3-3 on page 53

6. Circuit Breakers • Protects circuits that are prone to overloading • Some reset themselves, others must be manually reset • Commonly used with head lights & power seats

7. ECB – Electronic Circuit Breakers • 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

8. Switches • 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

9. Switches • SPST –Single pole single throw • Pole - number of input circuits • Throw – number of output circuits • SPDT – Single pole double throw • Ganged switch – several contacts move together, affect several circuits • Mercury switch – detects motion

10. Relays • Device that uses low current to control a high current circuit • Electro-magnetic switch

11. Solenoids • 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

12. Variable 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

13. Electronic Components

14. Diodes • One way electrical valve • Zener Diode – Allows voltage to pass in the opposite direction when voltage exceeds a certain limit

15. LED – 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

16. Clamping Diode • Used to suppress voltage spikes • Wired in parallel with a electromagnetic coil – A/C clutch • Connected to the circuit in reverse bias

17. Transistor • Regulates current or voltage and acts as a switch or gate for electronic signals • Solid state switching device

18. Phototransistors • 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

19. Phototransistor • Used on GM power sliding doors to monitor door movement and location

20. Circuit Defects • Open – A break in circuit continuity, stops current flow • Short – Current bypasses the normal circuit path • Short to ground • Short to power • Short to another circuit • High Resistance – unwanted opposition to current flow