EVT EVT Charging Systems & Infrastructure 2 — Questions and Answers
Question 1: What does a Ground Fault Circuit Interrupter (GFCI) monitor in an EVSE installation to protect users?
- Battery state of charge
- Current imbalance between hot and neutral conductors (Correct answer)
- Voltage drop across the charging cable
- Pilot signal duty cycle
Correct answer: Current imbalance between hot and neutral conductors
A GFCI detects a difference between the current on the hot and neutral conductors—indicating current is leaking to ground—and interrupts the circuit.
Question 2: A DC fast charger rated at 150 kW charges a vehicle with a 400V battery pack. Approximately how many amps does it deliver?
- 200 A
- 300 A
- 375 A (Correct answer)
- 600 A
Correct answer: 375 A
Current = Power / Voltage = 150,000 W ÷ 400 V = 375 A.
Question 3: What is the primary function of the on-board charger (OBC) in an electric vehicle?
- Convert DC from the battery to AC for the motor
- Convert AC grid power to regulated DC for battery charging (Correct answer)
- Manage thermal runaway in the battery pack
- Control regenerative braking torque
Correct answer: Convert AC grid power to regulated DC for battery charging
The OBC converts AC supply voltage from the grid or EVSE into the correct DC voltage and current needed to charge the high-voltage battery pack.
Question 4: When inspecting a CHAdeMO DC fast-charge port, a technician notices severe corrosion on the large power pins. What is the FIRST corrective action?
- Apply dielectric grease and return to service
- Clean with wire brush and retest resistance
- Tag out, remove from service, and replace the inlet assembly (Correct answer)
- Increase charge current to burn off oxidation
Correct answer: Tag out, remove from service, and replace the inlet assembly
Corroded high-current DC inlet pins can cause arcing, overheating, or fire; the inlet must be taken out of service and replaced before reuse.
Question 5: Which EVSE level provides the fastest charging rates currently available to passenger EVs at public stations in the US?
- Level 1 AC (120V)
- Level 2 AC (240V)
- DC Fast Charge (Level 3) (Correct answer)
- Wireless inductive charging
Correct answer: DC Fast Charge (Level 3)
DC Fast Charge (Level 3) stations deliver power directly as DC at up to 350+ kW, far exceeding Level 1 and Level 2 AC rates.
Question 6: What does a 'State B' Control Pilot signal (CP oscillating between +9V and -12V) indicate in a J1772 session?
- Vehicle not connected
- Vehicle connected, not ready to accept energy (Correct answer)
- Vehicle connected and requesting energy
- EVSE fault detected
Correct answer: Vehicle connected, not ready to accept energy
State B (CP between +9V and −12V, PWM present) means the vehicle is connected and detected, but the vehicle has not yet closed its contactors to accept power.
EVT EVT Charging Systems & Infrastructure 2
What does a Ground Fault Circuit Interrupter (GFCI) monitor in an EVSE installation to protect users?