EV Electrical 101: Understanding the Jargon and the Math

How Not to Get Lost in Volts, Amps, and Kilowatts

Switching to an EV means you’ll start hearing words like Level 2, kilowatts, breaker size, and amp draw — sometimes in the same sentence. Don’t panic. Here’s a quick breakdown of the key terms, plus the formulas and examples you can use to figure out how fast your car will charge and how far you can go.

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Key EV Charging Terms

Volts (V) – Think of voltage like water pressure in a pipe. In the U.S., most homes have 120V (normal outlets) and 240V (big appliances, EV chargers).

• Level 1 charging = 120V

• Level 2 charging = 240V

Amps (A) – This is the flow rate of electricity — like how much water is coming out of the pipe at once. Bigger amps = faster charging (up to your car’s limit).

Kilowatts (kW) – This is how much power your charger is sending to the car. It’s the product of volts × amps ÷ 1000.

• Example: 240V × 32A ÷ 1000 = 7.68 kW

Kilowatt-hours (kWh) – This is the EV equivalent of gallons in a gas tank. It measures how much energy is stored in the battery.

• Example: A 2020 Chevy Bolt has a 66 kWh battery.

State of Charge (SoC) – This is your “fuel gauge,” usually shown as a percentage.

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The Charging Math

Formula:

Charging time (hours) = Energy needed (kWh) ÷ Charger power (kW)

Step-by-step example:
Let’s say you have a 2020 Chevy Bolt with a 66 kWh battery, and you’re at 50% charge. That means you need 33 kWh to fill it.

At 20 amps:

240V × 20A ÷ 1000 = 4.8 kW
33 kWh ÷ 4.8 kW ≈ 6.9 hours

At 30 amps:

240V × 30A ÷ 1000 = 7.2 kW
33 kWh ÷ 7.2 kW ≈ 4.6 hours

At 32 amps (Bolt max):

240V × 32A ÷ 1000 = 7.68 kW
33 kWh ÷ 7.68 kW ≈ 4.3 hours

So yes — even at 20A, you’ll easily fill up overnight from 50%.

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Range Math

A 2020 Bolt gets about 4 miles per kWh under normal driving.

• Full charge (66 kWh) × 4 mi/kWh = ~264 miles

• 33 kWh (50% charge) × 4 mi/kWh = ~132 miles

Your real range will vary based on speed, weather, terrain, and use of heat/AC.

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Common EV Charging Lingo You’ll Hear

• Level 1 – 120V charging (slow, adds 3–5 miles per hour)

• Level 2 – 240V charging (fast home charging, adds 20–40 miles per hour)

• DC Fast Charging (Level 3) – Big public chargers that can take a Bolt from 0–80% in about an hour.

• Onboard Charger – The charger inside your car that limits how fast you can charge. The Bolt’s onboard charger maxes out at 32A on Level 2.

• Breaker Size – The circuit breaker size in your panel. You need 125% of your charger’s continuous draw, so a 32A charger needs a 40A breaker.

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Bottom Line

You don’t need an electrical engineering degree to own an EV. A little bit of math and a few key terms are all it takes to figure out how fast you can charge, how far you can go, and whether your setup is right for your needs.

Picking A Charger

Here is an article from this blog about the charger I picked for my Chevy Bolt.