EVITP Medium/Heavy-Duty, Fleet and DC Fast Charging Installations — Questions and Answers
Question 1: What supply is most commonly used to feed commercial DC fast chargers in the United States?
- 120 V single-phase
- 208 V single-phase
- 480 V three-phase (Correct answer)
- 12 kV single-phase
Correct answer: 480 V three-phase
Most U.S. commercial DC fast chargers take a 480 V three-phase supply, which delivers high power at manageable conductor sizes.
Question 2: Which SAE standard covers automated overhead (pantograph) conductive charging, as used for transit buses?
- SAE J1772
- SAE J3105 (Correct answer)
- SAE J2954
- SAE J1939
Correct answer: SAE J3105
SAE J3105 defines automated conductive charging through connection devices such as overhead pantographs, which are common at transit bus layover points.
Question 3: What is the Megawatt Charging System (MCS) mainly designed for?
- Residential Level 2 charging
- Electric bicycles and scooters
- Heavy-duty trucks and buses that need multi-megawatt charging (Correct answer)
- Wireless charging of passenger cars
Correct answer: Heavy-duty trucks and buses that need multi-megawatt charging
MCS, standardized as SAE J3271, is a high-power DC connector system for Class 8 trucks and other heavy-duty vehicles with very large battery packs. It supports power in the megawatt range.
Question 4: Why do many high-power DC fast chargers use liquid-cooled charging cables?
- To cool the vehicle's battery directly
- To carry very high current with a cable that stays light and flexible enough to handle (Correct answer)
- To meet ADA reach-range requirements
- To remove the need for a ground conductor
Correct answer: To carry very high current with a cable that stays light and flexible enough to handle
At several hundred amps, an air-cooled cable would need very large conductors and become too heavy for users to handle. Liquid cooling removes heat so the cable can stay smaller.
Question 5: A transit depot plans to charge 10 buses at the same time, each on a 150 kW charger. What is the peak charging demand?
- 150 kW
- 750 kW
- 1.5 MW (Correct answer)
- 15 MW
Correct answer: 1.5 MW
10 × 150 kW = 1,500 kW, or 1.5 MW. Loads this size often need utility coordination, a dedicated transformer and possibly managed charging.
Question 6: In DC fast charging, where is AC power converted to DC for the battery?
- In the vehicle's onboard charger
- In the off-board charger, so DC goes straight to the battery (Correct answer)
- In the utility transformer
- In the charging cable connector
Correct answer: In the off-board charger, so DC goes straight to the battery
A DC fast charger has its own off-board power electronics and sends DC directly to the battery, bypassing the vehicle's lower-power onboard charger.