What Is Onboard Charger in EV: Simple Explanation and Uses

An onboard charger in an electric vehicle (EV) is a device inside the car that converts AC electricity from a charging station into DC electricity to charge the EV's battery. It controls the charging speed and ensures the battery is charged safely and efficiently.

How It Works

The onboard charger acts like a translator inside your EV. When you plug your car into a regular power outlet or a public charging station, the electricity coming in is alternating current (AC). However, the EV battery needs direct current (DC) to charge properly. The onboard charger converts this AC power into DC power.

Think of it like a kitchen blender: you put in whole fruits (AC power), and it blends them into a smoothie (DC power) that the battery can use. It also controls how fast the battery charges by adjusting the power flow, protecting the battery from damage due to too fast or too slow charging.

Example

This simple Python example simulates how an onboard charger converts AC power to DC power and controls charging speed.

python

class OnboardCharger:
    def __init__(self, max_power_kw):
        self.max_power_kw = max_power_kw  # Maximum charging power in kilowatts

    def convert_ac_to_dc(self, ac_power_kw):
        # Converts AC power to DC power, limited by max power
        dc_power_kw = min(ac_power_kw, self.max_power_kw)
        return dc_power_kw

    def charge_battery(self, ac_power_kw, battery_capacity_kwh, current_charge_kwh):
        dc_power_kw = self.convert_ac_to_dc(ac_power_kw)
        # Simulate charging for 1 hour
        new_charge = current_charge_kwh + dc_power_kw
        if new_charge > battery_capacity_kwh:
            new_charge = battery_capacity_kwh  # Battery full
        return new_charge

# Example usage
charger = OnboardCharger(max_power_kw=7)  # 7 kW onboard charger
battery_capacity = 50  # 50 kWh battery
current_charge = 10  # 10 kWh currently charged
ac_power_input = 10  # 10 kW power from outlet

new_charge = charger.charge_battery(ac_power_input, battery_capacity, current_charge)
print(f"Battery charge after 1 hour: {new_charge} kWh")

Output

Battery charge after 1 hour: 17 kWh

When to Use

Onboard chargers are used whenever an EV is charged from an AC power source, such as home wall outlets or public AC charging stations. They are essential for everyday charging because most places provide AC power, not DC.

For example, if you plug your EV into a standard home socket overnight, the onboard charger manages the power conversion and charging speed safely. For faster charging, some EVs use external DC fast chargers that bypass the onboard charger, but onboard chargers are still needed for regular charging.

Key Points

• An onboard charger converts AC electricity to DC for the EV battery.
• It controls charging speed to protect the battery.
• Used mainly for charging from home or public AC power sources.
• Limits maximum charging power based on its design.
• Essential for safe and efficient battery charging inside the vehicle.

Key Takeaways

An onboard charger converts AC power to DC power inside an EV for battery charging.

It controls charging speed to ensure battery safety and efficiency.

Used mainly when charging from AC power sources like home outlets.

Onboard chargers have a maximum power limit that affects charging speed.

DC fast chargers bypass the onboard charger for quicker charging.