One of the most important technical specifications of an electric vehicle is the speed at which it can refuel at home. Every EV has an onboard charger that converts alternating current into direct current so that the electricity can then be delivered to the vehicle’s battery. Level One and Level Two home charging stations supply alternating current that has to pass through the EV’s onboard charger. The maximum speed at which the onboard charger can receive and convert alternating current is referred to as its “acceptance rate”, and is measured in kilowatts. Level Three fast chargers use 480 volts to deliver direct current straight to the battery, bypassing the onboard charger, but these expensive, industrial strength public chargers are meant to get long-distance motorists back on the road quickly and are not suitable for home installations. Level One trickle-chargers are quite slow, but allow EVs to be plugged into any existing 120 volt AC receptacle. Onboard chargers are designed to maximize the charging capabilities of Level Two home charging stations, which can deliver anywhere from 12 to 64 amperes of continuous current at 240 volts.
The amperage of the Level Two home charging station determines how fast it can deliver AC electricity to the EV, and the kilowatt rating of the EV’s onboard charger determines how fast it can accept it. If a charging station dishes out the electricity more slowly than the onboard charger can accept it, it limits how fast the EV’s battery charges. Typically, the homeowner installs a charging station with sufficient amperage, and the charging speed is limited by the onboard charger’s acceptance rate. Automakers are designing EVs to facilitate overnight charging, matching batteries with onboard chargers that are fast enough to refuel them before the sun comes up.
Onboard chargers with acceptance rates of 7.2 to 7.4 kilowatts are generally considered fast enough to refuel overnight, replacing about 29 miles of range per hour of charging. They match up nicely with popular 32 amp home charging stations that require a standard 40 amp circuit breaker. 32 amps at 240 volts deliver about 7.7 kilowatts of power, slightly exceeding the acceptance rates of these common onboard chargers. A faster 40 amp charging station could deliver 9.6 kilowatts, but the electricity would not pass through these onboard chargers any faster.
Some state-of-the-art, long-range EVs now feature even faster onboard chargers. The 2022 Ford Mustang Mach E, 2022 Chevy Bolt and Bolt EUV, 2022 Volkswagen ID.4, and most of the latest Teslas have onboard chargers with blazing AC acceptance rates of 10.5 to 11.5 kilowatts. They can utilize all the output of a faster 40 amp charging station that can deliver 9.6 kilowatts, and almost all the output of 48 amp units that can deliver 11.5 kilowatts. These highly capable home charging stations correspond to 50 and 60 amp circuit breakers. When paired with faster onboard chargers, they allow these premium EVs to replace up to 44 miles of range in one hour. The charging equipment is more expensive to install but provides a useful advantage when refueling the larger batteries overnight.
In order to maximize the speed of AC refueling, powerful home charging stations need onboard chargers with superior acceptance rates, and these EVs have what it takes.
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