What is an On-board Charger?
The part that lets you charge from a normal home or destination AC charger.
Simplified animation — not to scale.
In plain English
The on-board charger (OBC) lives inside the car and is used whenever you plug into an AC source — a home wallbox, a 3-pin plug or a public Type 2 destination charger. Its job is to convert that AC electricity into DC at the right voltage to charge the traction battery. Its size (typically 3.6kW, 7kW, 11kW or 22kW) is what limits your home charging speed — not the wallbox.
"Think of it as a built-in phone charger brick for your car. A wallbox is just a tap delivering AC — the OBC inside the car is the actual charger turning it into something the battery can drink."
How it works
When you plug in an AC charger, mains electricity flows into the OBC. It first rectifies it to DC, then steps it up to the high voltage the battery needs (often 400V+). DC rapid chargers bypass the OBC completely and feed the battery directly — which is why rapid charging is much faster than home charging.
Signs of trouble
- ⚠Car charges much slower than expected on AC
- ⚠"Charging fault" message
- ⚠Charging stops randomly
- ⚠No charging on AC but DC rapid still works
- ⚠Burning smell or warm charge port
£1,150 – £3,700
Always get a written quote. Prices vary by car, region, and parts brand.