What Is an Onboard Charger in Electric Vehicles? Simplified

Imagine bringing home a brand-new electric car like the Tata Nexon EV, MG Windsor EV Pro, or Mahindra BE.06. You park it, plug it into the wall socket or a home charger, and expect it to charge overnight—just like your phone.

But what many people don’t realise is there’s a hidden hero inside your EV, quietly doing the real work.

That hero is called the onboard charger.

So, What Exactly Is an Onboard Charger?

Let’s say you’re filling a water tank. If you use a garden pipe, it’ll take a while. But if you use a thick inlet pipe, the tank fills up much faster.

That thick pipe is what the onboard charger represents. The higher its kilowatt (kW) rating, the faster your car can charge using AC power.

For example, if you install a 7 kW wallbox at home but your EV only supports 3.3 kW through its onboard charger, you’ll still be limited to that slower 3.3 kW speed. So it’s not just the charger on the wall that matters—it’s also about what’s built inside your car.

Why Can’t EV Batteries Use AC Power Directly?

Think of your EV battery like a guest at a dinner party who will only eat food that’s fully cooked and ready to serve. But the electricity from your wall is like raw ingredients—it’s AC (alternating current) and your battery only digests DC (direct current). Know the difference between AC and DC charging in depth

The onboard charger works like the in-house chef. It takes those raw AC ingredients and prepares a nice, cooked DC meal—exactly how your battery likes it.

DC Fast Charging: How It Bypasses the Onboard Charger

While your onboard charger is the hardworking chef converting AC power into DC, DC fast chargers skip the kitchen altogether. Instead of passing electricity through the onboard charger, DC fast chargers send power directly to your EV’s battery. This is why DC fast charging is significantly faster—because it eliminates the conversion step and delivers high-voltage DC straight to the battery, often at speeds ranging from 50 kW to 350 kW, depending on what your EV supports.

Think of it like ordering pre-cooked meals instead of cooking from scratch—your battery gets exactly what it needs, instantly.

Where Is the Onboard Charger Located?

You won’t find it lying around in the boot or glovebox. The onboard charger is built into the EV, usually located under the hood or beneath the floor, close to the powertrain. You’ll never directly interact with it, but every time you plug into an AC charger, it’s doing the conversion quietly in the background.

How Onboard Chargers Regulate Voltage and Current?

Your onboard charger isn’t just a simple converter—it’s a smart regulator that ensures your battery gets the right amount of power without overheating or overcharging. It dynamically adjusts voltage and current based on the battery’s state of charge.

Scan the barcode and download the EVJoints app to find 6,000 EV charging stations across various networks.

Click & download the EVJoints app to find 6,000 charging stations.

Here’s how it works:

• Rectification: Converts AC into DC using diodes and transistors.
• Power Factor Correction (PFC): Aligns input current with voltage to improve efficiency.
• DC-DC Conversion: Fine-tunes voltage and current levels to ensure safe charging.

This regulation is crucial because EV batteries have strict charging limits. Too much power? You risk overheating or damaging the cells. Too little? Charging drags on. The onboard charger strikes the perfect balance, ensuring your battery gets the right amount of power every time you plug in.

Why Does the Onboard Charger Matter?

If you plan to charge your EV at home or at work using AC sources, the onboard charger plays a big role in how fast your car charges.

For instance:

• The MG Comet EV comes with a 3.3 kW onboard charger, meaning even if you have a 7.4 kW AC charger at home, your EV will still charge at 3.3 kW.
• The MG Windsor EV Pro features a 7.4 kW onboard charger, so it can make better use of faster AC wallboxes.
• The newly launched Mahindra BE 6 and XUV 9E come with powerful 11 kW onboard chargers, making home charging a lot quicker—provided your setup supports it.

Key Takeaways:

• What it does: Converts AC electricity from a charger into DC electricity your battery can store
• Where it lives: Built inside your EV—usually under the floor or hood
• Why it matters: Determines how fast your EV can charge from AC sources like home wallboxes
• Speed check: Charging speed is limited by the onboard charger’s rating—even if your external charger is faster

Real-Life Example:

If your car supports 3.3 kW onboard charging and you plug into a 7.4 kW AC wall charger, you’ll still only get 3.3 kW speed. But if your EV has an 11 kW onboard charger, like the Mahindra XUV 9E, then that same wall charger can charge your car much faster.

So before you invest in a fancy wall charger, check what your EV can handle internally.

Final Word

The onboard charger isn’t as flashy as your infotainment screen or as hyped as your EV’s range—but it’s working hard behind the scenes every single time you plug in. It quietly converts power to make sure your battery gets what it needs.

And now that you know what it does, you’ll never look at charging the same way again.

So when someone talks about “onboard chargers,” you can nod confidently and say:

“Yep, I know that guy. He’s the real MVP under the hood.”