What is an onboard charger in an electric vehicle?
An onboard charger (OBC) is the vehicle equipment that converts alternating-current electricity into direct current for its battery [S1]. Its rating limits AC charging: an 11 kW vehicle cannot use a chargepoint's full 22 kW output [S2]. Check the exact vehicle specification, cable and site settings before estimating charging time for your business. Checked October 2026.
What does an onboard charger do?
An onboard charger (OBC) is the equipment inside an electric vehicle that converts alternating current (AC) from the supply into direct current (DC) for the battery [S1].
Why it matters for your site: a higher-rated parking-bay chargepoint cannot force a vehicle to accept more AC power than its onboard equipment permits [S2]. Specify your fleet’s charging needs before ordering hardware.
A kilowatt (kW) measures power. A kilowatt-hour (kWh) measures energy. The onboard charger’s power rating and the battery’s energy capacity describe different limits [S2].
Why might a 22 kW point deliver only 7 or 11 kW?
The usable AC rate depends on the vehicle’s acceptance limit as well as the available supply. Energy Saving Trust explains that a vehicle limited to 7 kW remains limited when connected to a 22 kW point. It also identifies three-phase supply as a requirement for 22 kW AC charging [S2].
For your procurement schedule, record the exact vehicle variant’s AC limit, phase capability and arrival and departure times. Ask the installer to check the cable rating and any power-sharing settings. Read 7 kW versus 22 kW chargers for the wider site choice.
How does the limit affect charging time?
For an illustration, assume a vehicle needs 22 kWh and accepts a steady 11 kW. Time = 22 ÷ 11 = 2 hours, even at a 22 kW point. The assumed steady rate excludes losses and changes during charging [S1], [S2].
DC rapid charging bypasses the onboard AC converter, but vehicle and battery conditions still constrain the rate [S1]. Use battery sizes and charging curves to understand why peak power is not a whole-session average. Check energy expenditure with the charging cost tool.
Next step
List your vehicle variants and parking windows in the site check, then get matched with an installer that covers your area.
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Common questions
Can a vehicle with a 7 kW AC limit use a 22 kW point?
Yes, where the connection is compatible, but the higher point rating does not raise the vehicle's AC acceptance limit [S2].
Does a larger vehicle battery mean a faster onboard charger?
Do not infer AC power from stored energy. Check the vehicle's AC charge limit separately from the battery capacity when estimating turnaround time [S2].
What electricity supply does 22 kW AC charging need?
Energy Saving Trust identifies a three-phase building supply for 22 kW AC charging. Vehicle capability must also support the intended rate [S2].
Where does conversion happen during DC rapid charging?
The external chargepoint supplies direct current to the battery, bypassing the onboard AC charger. The vehicle still controls acceptable charging conditions [S1].
Can charging slow near a full battery?
Yes. Energy Saving Trust explains that charging power can fall as the battery approaches full capacity. A constant-power calculation is only an estimate [S1].
Ask about your site
Sources
- Types of chargepoint - AC or DC charging and smart management, Energy Saving Trust,Last checked 19 October 2026
- Charging your business's electric vehicles, Energy Saving Trust,Last checked 19 October 2026