Cars · Lesson 11 of 15Intermediate5 min read
Hybrids and Electric Cars
Electric drive replaces or helps the engine with motors that run on a high-voltage battery. Fewer moving parts and no oil changes make an electric car simpler to maintain, but its high-voltage system is one area where only trained technicians belong.
Hybrids, plug-ins and all-electric cars
- Hybrid (HEV): an engine plus one or more electric motors and a battery. It can’t plug in; it charges its battery with the engine and by regenerative braking. Mild hybrids help the engine and can shut it off at stops but can’t drive on electricity alone; full hybrids can drive short distances at low speed on electricity. In the most common design, a parallel hybrid, both the engine and the motor can turn the wheels.
- Plug-in hybrid (PHEV): a bigger battery you can charge from the grid, plus an engine for longer trips.
- All-electric (BEV): no engine at all; a large traction battery and one or more motors. No tailpipe, no fuel pump, no fuel tank.
What’s inside an electric car
The traction battery stores the energy. The power electronics controller manages the flow of energy from the battery and controls the motor’s speed and torque. The traction motor turns the wheels through a transmission. The onboard charger turns AC from a wall outlet into DC for the battery, and a DC/DC converter steps the high voltage down to run the accessories and recharge a separate 12-volt battery. A thermal system keeps the battery, motor and electronics in their working temperature range.
| Part | What it does | Signs of trouble |
|---|---|---|
| Traction battery pack | Stores the energy that drives the car. | Reduced range; warning messages. Service only by trained technicians. |
| Power electronics (inverter) | Control the flow of energy and the motor’s speed and torque. | Warning messages; a technician diagnoses it. |
| Traction motor | Drives the wheels; works as a generator when braking. | Unusual noises; warning messages. |
| Onboard charger | Turns AC from the grid into DC for the battery. | Charging problems on AC power. |
| Charge port | Where the charging cord connects. | Charging won’t start; visible damage. |
| DC/DC converter | Supplies the 12-volt system from the high-voltage battery. | 12-volt system problems. |
| 12-volt battery | Runs lights, instruments and computers. | Electrical problems; the car may not power on. |
| Thermal system | Keeps battery, motor and electronics at the right temperature. | Warning messages. |
The battery pack
Electric cars use lithium-ion cells. One cell makes about 3.7 volts, so a pack links many cells in series to reach a high voltage; high-voltage systems in electric vehicles typically range from 400 to 1,000 volts. Many manufacturers warranty their EV batteries for 8 years or 100,000 miles, and the Department of Energy expects batteries to last 12 to 15 years under normal conditions in moderate climates.
Regenerative braking
A motor becomes a generator when its shaft is turned. When you lift off the accelerator or press the brake, the car can use its motor that way, turning the wheels’ motion back into electricity for the battery instead of heat in the brakes. That recovered energy is a big part of why electric cars are so efficient: in combined driving, about 87 to 91 percent of the energy from the grid reaches the wheels, counting about 22 percent won back by regenerative braking. Brake wear drops a lot, too.
Charging levels
Charging speed is usually described as miles of range added per hour.
| Level | Power source | Range added |
|---|---|---|
| Level 1 | A standard 120-volt outlet, using the cordset most EVs come with | About 2 to 5 miles per hour |
| Level 2 | 240 volts at home (208 or 240 volts at work), on dedicated equipment | About 10 to 30 miles per hour |
| DC fast charging | Public stations; most plug-in hybrids can’t use them | About 100 to 200+ miles in about 30 minutes |
Maintenance
All-electric cars need less maintenance: fewer moving parts, and fewer fluids such as engine oil to change. Hybrids and plug-in hybrids still have engines, so their upkeep is much like a regular car’s. Tires, brakes, wipers, cabin filters and the 12-volt battery still need attention on every car (Lesson 14). One difference: the high-voltage battery can’t be jump-started. Your owner’s manual explains what to do if the car won’t power on.
StopHigh voltage is for trained technicians only
The high-voltage battery, its orange cables and everything connected to them can carry enough energy to kill. NHTSA’s advice is plain: never try to service the traction battery without proper training and specialized equipment, and always assume the high-voltage battery and its components are energized and fully charged. Don’t touch exposed electrical parts or damaged high-voltage components.
- After a crash, a flood or other damage, contact your dealer. Don’t store a badly damaged EV inside a building or within 50 feet of one; batteries can release flammable gases and catch fire later.
- If you see smoke, sparks or flames, or hear gurgling or bubbling from the battery, get away from the car and call 911.
Check yourself
Tap an answer to check it, or open “Show the answer.”
Which kind of hybrid can’t drive on electricity alone?
Show the answer
A mild hybrid. Mild hybrids help the engine but can’t power the car on electricity alone.
What turns AC from your wall outlet into DC for the battery?
Show the answer
The onboard charger. The onboard charger converts AC to DC and talks to the charging equipment.
About how much range does Level 2 charging add per hour?
Show the answer
10 to 30 miles. Level 2 adds about 10 to 30 miles of range per hour of charging.
How does regenerative braking slow the car?
Show the answer
The motor works as a generator and charges the battery. Turning the motor’s shaft makes it a generator, which takes energy from the car’s motion.
What color are the high-voltage cables in hybrids and EVs, usually?
Show the answer
Orange. High-voltage cables are typically marked orange. Treat them as off-limits.
Go deeper
- Lesson 12: Thrusters and Fans on the 2026 Roadster An electric car with cold-gas thrusters and suction fans, and the physics of both.
- U.S. Department of Energy, Alternative Fuels Data Center: How Do All-Electric Cars Work? Key parts of an all-electric car.
- U.S. Department of Energy, Alternative Fuels Data Center: Hybrid Electric Vehicles How hybrids work, mild to full.
- U.S. Department of Energy, Alternative Fuels Data Center: Electric Vehicles for Consumers (charging levels) Charging at home and on the road.
- NHTSA: Electric and Hybrid Vehicles: Battery, Charging and Safety NHTSA’s safety information for EV and hybrid owners.
Sources
- U.S. Department of Energy, Alternative Fuels Data Center: Hybrid Electric Vehicles
- U.S. Department of Energy, Alternative Fuels Data Center: How Do Plug-In Hybrid Electric Cars Work?
- U.S. Department of Energy, Alternative Fuels Data Center: How Do All-Electric Cars Work?
- U.S. Department of Energy, Alternative Fuels Data Center: Electric Vehicles for Consumers (charging levels)
- U.S. Department of Energy, Alternative Fuels Data Center: Maintenance and Safety of Electric Vehicles
- U.S. Department of Energy: Electric Vehicle Basics (DOE/GO-102023-6050, 2023)
- FuelEconomy.gov (DOE and EPA): Where the Energy Goes: Electric Cars
- OpenStax Chemistry 2e, 17.5 Batteries and Fuel Cells
- OpenStax College Physics 2e, 23.5 Electric Generators
- NHTSA: Electric and Hybrid Vehicles: Battery, Charging and Safety
- NHTSA: Interim Guidance for Electric and Hybrid-Electric Vehicles Equipped With High Voltage Batteries, Vehicle Owner/General Public (DOT HS 811 574)
- NHTSA: Interim Guidance for Electric and Hybrid-Electric Vehicles, Law Enforcement/EMS/Fire (DOT HS 811 575)
A free course from Teddy Rook Book. It explains how cars work in general and follows U.S. sources; your owner’s manual and your vehicle’s service information are the final word for your car, along with state and local rules.