Electrical and Electronics Fundamentals for EVs
What this domain covers
This domain tests basic electricity as it appears on an EV: voltage, current, resistance, power, DC and AC, series and parallel circuits, and the meters and components used to test them.
Core rules and concepts
- Ohm's law: V = I × R. Power: P = V × I, and P = I²R for heating.
- DC and AC: batteries store DC; the grid and motor phases are AC. The inverter changes DC to AC; the onboard charger changes AC to DC.
- Series: voltages add, current is common, Ah capacity stays the same. Parallel: capacity adds, voltage stays the same.
- Circuit protection: fuses melt, relays switch small currents, contactors switch HV, precharge resistors limit inrush.
- Measurement: voltmeter in parallel, ammeter in series or with a clamp, ohmmeter only on a dead circuit.
- Signals: sensors feed the ECU; CAN bus carries digital data between controllers.
Worked example
A 48 V pack is rated 20 Ah. What is its energy, and what current does a 12 V 24 W lamp draw? Energy = 48 × 20 = 960 Wh = 0.96 kWh. Lamp current = 24 ÷ 12 = 2 A. If ten 3.2 V cells are series-connected, pack nominal voltage is 32 V; the Ah rating does not add in series.
Traps that cost marks
Never measure current by placing the meter across a battery - it acts as a short circuit and blows the fuse. Do not write Ah when you mean A. Do not assume series connection raises capacity. Do not use an AC clamp meter on DC cables and expect a correct reading. Do not test resistance on a live HV circuit.