Why Your EV Charges at 7kW When the Charger Offers 22

I plugged into a 22kW post outside a supermarket in March expecting to be done in a little over two hours. The app said 22kW. The sign on the unit said 22kW. The car settled at 7.3kW and stayed there, and my two hour stop turned into a six and a half hour stop that I did not have time for. I spent the wait reading the car's spec sheet properly for the first time, which I should have done before buying it.

This is the single most common complaint I get by email about AC charging, and almost every time the charger is working exactly as designed. The bottleneck sits inside the car, in a box most owners have never heard of, and the number printed on it is fixed for the life of the vehicle. Worth understanding before you pay for a home installation or plan a trip around destination charging.

The onboard charger is the ceiling

Batteries store direct current. The grid delivers alternating current. Something has to convert one into the other, and on AC charging that job belongs to a unit bolted into the car called the onboard charger. Its rating decides your maximum AC speed and nothing outside the car can raise it.

DC fast charging is a different path entirely. There the conversion happens in the roadside cabinet, which is why the same car that crawls at 7kW on a lamppost can take 150kW at a motorway services. If the distinction between the rate and the amount still feels slippery, I worked through it in kW vs kWh in EV charging.

So the sequence that decides your actual speed is: the supply at the post, the cable, the onboard charger, and then the battery management system. You get the lowest of the four. In practice the onboard charger wins the race to the bottom on nearly every AC session.

Where the numbers come from

AC charging power is just volts times amps times the number of live phases. Most of Europe runs 230 volts per phase. The common ratings fall out of that arithmetic, and once you have seen the table you can predict what any post will give you.

Here is the part that catches people out. A car with an 11kW onboard charger standing at a 22kW three phase post will take 11kW, as expected. The same car on a single phase 32A supply at home takes 7.4kW, because two of the three phases it was designed to use are simply not there. Nothing is faulty. The car cannot invent a phase.

And a car with a 7.4kW single phase onboard charger plugged into that 22kW post takes 7.4kW, which is what happened to me. The post was fine. My car was the limit.

Buying the bigger onboard charger is usually wasted money

The standard advice on forums is to tick the upgraded AC charger option when you order, because you will regret it later. I disagree for most drivers, and the arithmetic is not complicated.

At 7.4kW, eight hours parked overnight puts roughly 59kWh into the battery. That is a full charge on most cars sold today and more than a full charge on a smaller one. Going to 11kW gets you there in five and a half hours instead. If your car sleeps on your drive from 7pm to 7am, you have paid several hundred pounds to finish at two in the morning rather than half past midnight, while you were asleep.

The upgrade earns its money in three situations, and they are specific. You charge at a shared 22kW post in an apartment car park where other residents are waiting. You regularly do same day return trips that need a top up in the middle of the working day. Or you drive somewhere, like much of mainland Europe, where three phase at home is standard and the 11kW is cheap or included anyway.

If none of those describe you, put the money into getting the home installation right instead. I set out that decision in whether to install a home charger or stick with a wall plug.

What your car actually accepts, and how to confirm it

Manufacturer figures vary by trim and by model year in ways the marketing pages blur, so treat anything you read, including the examples below, as a prompt to check your own documents rather than as the answer.

The Nissan Leaf has shipped for years with a 6.6kW onboard charger, so a 22kW post gives it 6.6kW. The Renault Zoe was the outlier in the other direction, with a Chameleon charger that genuinely took the full 22kW on AC, which made it a far better city car than its DC figures suggested. Tesla Model 3 and Model Y are 11kW three phase. The VW ID.3 arrived with 7.2kW as standard on lower trims and 11kW as an option, which is exactly the kind of split that gets lost in a used listing.

Three checks, in order of reliability. Find the line in your owner's handbook under AC charging or onboard charger, given in kW along with a phase count. Then look at the car's own charging screen mid session, which on most models shows amps per phase; three numbers near 16 means three phase at 11kW, a single number near 32 means single phase at 7.4kW. Then check the charge current limit setting in the car, because a reduced limit you set once at a friend's house with a questionable socket stays set until you change it back.

When the number is low and it is not the onboard charger

Years of filing bug reports taught me to rule out the dull causes before blaming the design, and the dull causes are the common ones here.

A granny cable is almost always pegged at 10A or 13A, around 2.3kW to 3kW, and no setting will lift that. A portable cable sold as 32A may carry a 20A plug; the rating moulded into the connector housing is the one that counts. Cold weather makes the battery management system request less current until the pack warms, which looks identical to a charger fault and resolves itself in twenty minutes. A dynamic load balancing device on a home installation will throttle your charge when the oven and the shower are both running, which is the system working.

And some public AC posts labelled 22kW are wired as single phase at the kerb, especially retrofits in older car parks. If you see 7.4kW on a car you know takes 11kW, that is the most likely explanation. You can confirm it from the amps per phase readout rather than guessing. Which cable and connector you are holding matters too, and the varieties are covered in EV charging connector types.

FAQ

Can an onboard charger be upgraded later?

On almost every car, no. It is a sealed high voltage component integrated with the power electronics, and no manufacturer sells a retrofit path. Software updates do not change the rating either, whatever a forum post claims.

Does charging at 7.4kW instead of 11kW harm the battery?

No, and if anything the slower AC rate is the gentler of the two. Pack degradation tracks heat, high states of charge and frequent DC fast charging far more closely than it tracks AC power.

Why does my 11kW car take 11kW abroad but 7.4kW at home?

Because your home supply is single phase and the destination had three phase. Same car, same cable, different number of live conductors. Getting three phase brought into a house is possible but usually costs more than the charging time it saves.

Is a 22kW home charger worth installing?

Only if you already have a three phase supply and a car that can use it, which is a small overlap. Otherwise the unit will spend its life delivering 7.4kW while costing more than a 7.4kW unit would have.