When you plug a car into a Level 2 charger, you might expect the charger on the wall to set the speed. In most cases it does not. For AC charging, the car's own onboard charger converts alternating current from the grid into direct current for the battery, and it sets the maximum rate the car will accept. This article explains how that works and why a more powerful home charger may not charge a particular car any faster.
AC power and the battery
The grid and Level 2 chargers supply alternating current (AC). Batteries store and release direct current (DC). The conversion from AC to DC happens inside the car, in a component called the onboard charger. The home charger mainly delivers AC power and communicates with the car about how much current is available.
What the onboard charger limits
Each car has a maximum AC charging power that its onboard charger can handle. This limit is often expressed in kW, and it can be lower than the rating of the charger on the wall. If a car's limit is 7.2 kW, a 9.6 kW or 11.5 kW charger will still deliver only about 7.2 kW to that car. The charger cannot force more power into the car than the onboard charger accepts.
Why the slower limit wins
The speed of a charging session is set by its weakest link, which could be the charger, the cable, the circuit, or the onboard charger. In an AC session, the onboard charger is often the limit. A higher-rated home charger does not speed up a car that cannot accept the extra power.
Checking your car before you choose a charger
- Find the AC charging rate. The car's owner's manual or specification sheet lists its maximum AC power in kW.
- Compare against the charger. If the car's limit is lower than the charger's rating, the extra amperage will not add speed for that car.
- Consider future cars. A charger rated above your current car's limit can still be useful if you change vehicles later.
- Know the difference with DC. Fast public DC charging supplies direct current to the battery, so it does not depend on the car's onboard charger.
Other factors that affect speed
The onboard charger is one factor among several. Battery temperature and state of charge also affect the rate, and the circuit must be able to supply the charger's rated amperage. Charging cables and connectors in good condition help the session run at its planned rate.
How this applies to EVIQO chargers
EVIQO chargers come in 40-amp (9.6 kW) and 48-amp (11.5 kW) versions for 240-volt circuits, with a 25 ft cable and a 3-year warranty. Because the car's onboard charger may set the speed, check the car's AC rate before choosing between the two. If the car's limit is below 9.6 kW, the 40-amp and 48-amp chargers will deliver the same rate, and the 40-amp NEMA 14-50 plug-in option may be enough.