How many kW do I need for my home EV charger?

You need as many kWs as your EV’s onboard charger can accept, or less. Every vehicle’s tech spec sheet indicates the maximum power in kW that its onboard charger can accept. The most common are 7.6kW, 9.4kW, or 11kW.

How fast can I charge my car at home?

It depends on two major factors - your car’s ability to accept power and your charger’s amperage. At home, you cannot charge faster than your vehicle’s onboard charger’s limit, or faster than the power output of your EV home charger. Ideally, they should match.

However, the confusion for a common EV owner comes because of different metrics used to define an EV’s ability to accept power and an EV charger’s power output. The first is usually presented in kWs and the second one in amps.

How to convert amps to kW?

The equation is relatively simple:

the amount of kW your Level 2 charger will feed to your EV equals the amperage of your EV charger times the voltage of the current. The formula for EV charging is below

P(kW) = (I(A) * V(V)) / 1000

So, if you have a 40 amp charger on a 240-volt outlet, your EV will be charged at the maximum power of:

(40 * 240) / 1000 = 9.6kW

What is the fastest way to charge an EV at home?

Level 2 charging is a homeowner’s best choice for EV charging. Level 1 charging happens on a standard 110-volt wall outlet, while Level 2 charger use more powerful 240-volt outlets and come with variable amperage settings.

The formula for calculating amperage is:

I(A) = (P(kW) * 1000) / V(V)

For example, for a Rivian, the max AC rate is 11.5kW, therefore the most optimal charger for Rivian will be:

I(A) = (11.5kW * 1000) / 240V = 48 amps

What is the difference between 40A and 48A chargers?

48A chargers need to be hardwired and in many cases require not only a licensed electrician but also a permit for the electrical work. 48A chargers use 60A breakers and 6 gauge cabling, which makes the installation of such a charger more expensive.

Meanwhile, 40A chargers plug into an outlet (commonly the NEMA 14-50). They are easier to install, replace, and require less available amperage from your electrical panel. All you lose is the difference between charging your car at 9.4kW vs. 11kW.

How much power do I need for a Level 2 EV charger at home?

Most homes pull 60, 100, 200, or 400 amps of current. The Level 2 EV charger will often need between 40-60 amps of current.
Further, the National Electrical Code requires an electrical circuit to be rated for 25% greater amperage than your charger’s output. For example, if you want to buy a 40A Level 2 charger, you’ll need a circuit breaker that’s rated for at least 50 amps.
Your panel will also need to have enough physical space for the charger. Circuit breakers will need to be available for the charger. A certified electrician will be able to tell if there is enough space.