An on-board charger (OBC) is the part inside an electric vehicle that converts AC power from a home or public AC charger into DC power to charge the battery. Its power rating — typically 3.3 kW, 7.2 kW or 11 kW in Indian EVs — sets the maximum speed of AC charging. When you use a DC fast charger, the on-board charger is bypassed: the conversion happens inside the charging station, which is why DC charging is much faster.
Last updated: September 2026.
How an On-Board Charger Works
- AC input: AC power arrives through the car’s charging port (Type 2 on most Indian cars) from a wallbox or AC charger.
- Rectification and power factor correction: the OBC converts AC to DC and keeps the power drawn from the grid clean and efficient.
- DC-DC conversion: it adjusts the voltage and current to what the battery needs.
- Communication with the BMS: the battery management system tells the OBC how much current to deliver based on the battery’s charge level and temperature.
The AC wallbox on the wall is not really a “charger” in this sense — it is a smart, safe power supply that tells the car how much current it may draw. The actual charging is done by the OBC inside the car.
Why the On-Board Charger Limits AC Charging Speed
AC charging speed is the lowest of three numbers: the wallbox rating, your electricity supply and the car’s OBC rating. For example:
- A car with a 7.2 kW OBC charges at up to about 7.2 kW, even on a 22 kW AC charger.
- A car with an 11 kW OBC (such as the BMW iX1) needs a three-phase supply and an 11 kW or higher wallbox to charge at 11 kW.
- Many Tata EVs, including the Tiago EV and Curvv EV, use a 7.2 kW AC charging rate.
For how long that takes, see how much power is required for EV charging.
On-Board Charger vs DC Fast Charging
| AC charging (uses the on-board charger) | DC fast charging (bypasses it) | |
|---|---|---|
| Where AC-to-DC conversion happens | Inside the car, in the OBC | Inside the charging station |
| Typical power | 3.3–22 kW, limited by the OBC | 25–350 kW, limited by the charger and the car’s DC limit |
| Connector (cars in India) | Type 2 | CCS2 |
| Best for | Overnight home and workplace charging | Highway trips and quick top-ups |
See our guides to AC vs DC chargers and EV charger and connector types.
Types of On-Board Chargers
- Single-phase OBCs (typically 3.3–7.4 kW) — common in affordable cars and two- and three-wheelers.
- Three-phase OBCs (typically 11–22 kW) — found in some premium EVs for faster AC charging.
- Bidirectional OBCs — can also send power out of the battery, enabling vehicle-to-load (running appliances) or vehicle-to-home (for example, the MG Hector Tomahawk EV can act as an inverter during a power cut).
On-Board Charger Design Challenges
- Size and weight: every extra kilowatt of OBC capacity adds weight and takes space inside the car.
- Heat: converting several kilowatts continuously produces heat, so OBCs need cooling — important in Indian summers.
- Efficiency: modern OBCs are typically well above 90% efficient; newer designs use silicon carbide (SiC) power electronics to reduce losses and size.
- Cost: higher-power and bidirectional OBCs cost more, which is why many affordable EVs stop at 7.2 kW.
Related Reading
- How Much Power Is Required for EV Charging? kWh, kW and Home Load
- EV Charger and Connector Types in India: Type 2, CCS2, Bharat and More
- AC vs DC EV Chargers: Which One Is Best for Your EV Charging Station?
- V2G vs V2H vs V2L: Bidirectional EV Charging Explained
Learn more about AC EV chargers.
Frequently Asked Questions
What is an on-board charger in an electric vehicle?
It is the component inside the vehicle that converts AC electricity from a home or public AC charger into DC to charge the battery, while communicating with the battery management system.
Does DC fast charging use the on-board charger?
No. A DC fast charger converts AC to DC inside the charging station and feeds DC directly to the battery, bypassing the on-board charger.
What is the on-board charger rating of Indian EVs?
Many electric cars in India have a 7.2 kW on-board charger, and some models have 11 kW. Check your owner’s manual for the exact AC charging rate. Many two- and three-wheelers have smaller units.
Can I charge faster by buying a bigger AC wallbox?
Only up to your car’s on-board charger rating and your electricity supply. A 22 kW wallbox will not speed up a car with a 7.2 kW OBC; for faster charging, use a DC fast charger.