NAVTTC Auto Electrician flashcards
NAVTTC Auto Electrician · Build recall with a focused review session.
33 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Ohm's law
- Voltage equals current multiplied by resistance (V = I x R). In a 12 V circuit with a 6 ohm load, current is 2 A. Rearranged, R = V / I and I = V / R.
- Electrical power formula
- Power in watts equals voltage times current (P = V x I). A 55 W headlamp on 12 V draws about 4.6 A, which sets the fuse and wire size.
- Series circuit rules
- In a series circuit the same current flows through every component, total resistance adds, and the supply voltage divides across components in proportion to their resistance.
- Parallel circuit rules
- In a parallel circuit every branch sees the same voltage, branch currents add to give total current, and total resistance is lower than the smallest branch resistance.
- Volt drop test
- A measurement of voltage lost across a cable, connector or switch while current flows. Under 0.5 V total is normal for a 12 V high-current circuit; more indicates excess resistance.
- Parasitic drain test
- With all modules asleep, connect a meter in series at the battery negative. Normal drain is usually below 50 mA; a higher reading means a circuit is staying live.
- Short to earth
- An unintended low-resistance path from a supply wire to the chassis. It blows the fuse immediately and shows near 0 ohm between the isolated wire and earth.
- Open circuit
- A broken path so no current can flow. The load does not work, and a voltmeter reads full supply voltage across the break when the circuit is switched on.
- Six-step diagnostic sequence
- Verify the complaint, gather information, inspect the system, test to isolate the cause, repair, then verify the repair. Skipping verification leaves intermittent faults undetected.
- Battery open-circuit voltage
- After two hours rest a fully charged 12 V lead-acid battery reads 12.6 to 12.8 V. About 12.4 V is 75 percent charged and 12.0 V about 25 percent.
- Cold cranking amps (CCA)
- The current a battery delivers for 30 seconds at minus 18 degrees C while terminal voltage stays above 7.2 V. It rates starting ability in cold weather.
- Electrolyte specific gravity
- A fully charged lead-acid cell reads about 1.265. A reading near 1.120 means discharged; a spread above 0.050 between cells indicates a failed cell.
- Battery load test
- Apply half the CCA rating for 15 seconds at about 20 degrees C. A good battery holds at least 9.6 V; a lower reading means the battery is weak or discharged.
- Ampere-hour capacity
- The current a battery delivers for 20 hours down to 10.5 V. A 60 Ah battery supplies 3 A for 20 hours at room temperature.
- Batteries in series and parallel
- Series connection adds voltage and keeps capacity; parallel connection adds capacity and keeps voltage. Mixing age or capacity in either arrangement causes circulating currents.
- Battery terminal disconnection order
- Disconnect the negative (earth) terminal first and reconnect it last. This prevents a spanner touching bodywork from shorting the positive terminal through the chassis.
- Hydrogen gas hazard
- Lead-acid batteries release hydrogen while charging. It is explosive between about 4 and 75 percent in air, so flames, sparks and grinding must be kept away.
- Electrolyte first aid
- Battery acid is dilute sulfuric acid. Flush affected skin or eyes with clean water for at least 15 minutes, remove contaminated clothing, then get medical help.
- Electrical fire extinguisher
- Use carbon dioxide or dry powder on electrical and fuel fires. Never apply water to a live electrical fire because it conducts current and spreads the hazard.
- Multimeter current measurement
- Current is measured with the meter in series with the load. Connecting the meter in parallel on a current range shorts the supply and blows the meter fuse.
- Clamp meter use
- A clamp meter reads current from the magnetic field around one conductor. Clamping both the feed and return conductors cancels the fields and reads zero.
- Crimp versus solder
- A correct crimp resists vibration and is preferred for vehicle harness repairs. A soldered joint needs heat-shrink support because vibration can fatigue the wire at the joint.
- Feeler gauge use
- Feeler gauge blades are marked in millimetres or inches. A spark plug gap is correct when the blade drags slightly between the electrodes, not when it fits loosely.
- Relay terminal numbers
- Coil terminals are 85 and 86. Contact terminal 30 is the supply, 87 the switched load, and 87a the normally closed contact. A relay lets a small current switch a large one.
- Starter cranking current
- A passenger car starter draws about 150 to 250 A. Battery voltage should stay above 9.6 V during cranking; a lower reading points to a weak battery or high cable resistance.
- Alternator regulated voltage
- A healthy alternator holds about 13.8 to 14.4 V at 1500 rpm. Below 13.2 V means no charging; above 14.8 V causes gassing and water loss.
- Alternator ripple test
- Set a meter to AC volts across the battery with the engine running. Ripple above about 0.5 V AC indicates a failed rectifier diode and reduced output.
- Starter solenoid windings
- The pull-in winding engages the drive with high current; the hold-in winding keeps the contacts closed with lower current. A failed hold-in causes chatter or no crank.
- Ignition coil resistance
- Primary resistance is typically 0.5 to 2 ohms; secondary is 6 to 15 kilo-ohms depending on coil type. An open or very high reading means replace the coil.
- Crank position sensor fault
- The crank sensor gives engine speed and position. When its signal is lost the ECU stops both spark and injection, so the engine cranks but does not start.
- Spark tester gap test
- A spark tester set to a 6 to 8 mm gap confirms spark energy under load. It is more reliable than laying a plug on the block, which fires easily at atmospheric pressure.
- Fuse rating rule
- Choose a fuse about 1.5 times the circuit's normal current, so a 10 A circuit uses a 15 A fuse. A fuse that blows again means the overload or short is still present.
- Fast flasher symptom
- A turn signal flashing faster than normal usually means one bulb is open circuit, so the flasher sees less current. Check bulbs and earths before replacing the flasher.