Guide
7 kW vs 22 kW home EV chargers: what is the difference?
A 22 kW unit can deliver more power than a 7 kW unit, but only when the supply and car can use it. Start with your home's electrical assessment and the maximum AC charging rate of your exact car, rather than buying the largest number on the box.
Phases explained
Single-phase and three-phase, in plain English
This is the whole answer to the 7 kW or 22 kW question, and it is about your house rather than your car.
The number of phases describes how many live wires come into your property. A single-phase supply has one, at 230 volts. A three-phase supply has three of them, which together deliver far more power.
Almost every home in the UK is single-phase. Three-phase supplies are ordinary in shops, warehouses and industrial buildings, and they do turn up in some larger and newer homes, but they are the exception. Your installer can tell you which you have, and it is worth knowing before you start comparing chargers.
Here is the vocabulary you will meet on a product page or a quote:
- kW
- Kilowatts, a measure of power. It is a rate, not a total, so it describes how fast energy arrives rather than how much energy you take.
- Single-phase
- The standard electricity supply in almost every UK home. One live wire at 230 volts. It can deliver enough for a 7 kW charger and nothing more.
- Three-phase
- Three live wires instead of one, common in commercial premises and uncommon in homes. A 22 kW charger needs it.
- Onboard charger
- The converter inside your car that turns the alternating current from a wall unit into the direct current a battery stores. It has its own maximum, and that maximum is often lower than the wall unit's.
- AC
- Alternating current, the kind of electricity a home chargepoint supplies. Your car converts it. Public rapid chargers usually supply DC, which is why they need a different, larger inlet.
Why 7.4 kW
Why many home chargers are rated at 7.4 kW
At a nominal 230 volts, 32 amps corresponds to about 7.4 kW. That explains a common home-charger rating; it does not establish that every property can supply that current. An installer must assess the available capacity and design the circuit, protection and any load management.
A 22 kW charger works differently. It uses all three phases of a three-phase supply at 32 amps each, and the 230 volts across all three phases gives roughly 22 kW. On a single-phase home, the same unit simply cannot deliver that. Depending on the unit and the install, you would get single-phase behaviour, which means paying for a 22 kW label and charging at 7 kW.
The car decides
Your car still sets its own limit
Even with three-phase electricity at the door, your car sets the limit.
7.4 kW charger · Same car: 11 kW AC limit
At most 7.4 kW to the car
22 kW charger · Same car: 11 kW AC limit
At most 11 kW to the car
This is the part that surprises people. Your car converts AC into the DC its battery needs, and the converter has a fixed maximum. If that maximum is 7.4 kW, no wall unit in the world will charge that car faster at home.
A car with a 7.4 kW AC limit cannot take 22 kW from a 22 kW unit. A car with an 11 kW three-phase AC limit may benefit from a suitable three-phase installation, but still cannot draw 22 kW. The exact limit depends on the vehicle version and sometimes its optional charging equipment.
Find your own car's figure in its handbook or manufacturer's specification. Look for the maximum AC charging rate, and whether it is single-phase or three-phase.
How long
What the two speeds mean in hours
Published figures for charging from empty, by battery size.
The Energy Saving Trust publishes approximate charge times across battery sizes and power levels. They are a useful guide, but real charges take longer because charging slows down as the battery fills, and a car rarely starts completely empty.
| Battery size | 7.4 kW AC | 11 kW AC | 22 kW AC |
|---|---|---|---|
| 25 kWh | 3h 45m | 2h | 1h |
| 50 kWh | 7h 45m | 5h 15m | 3h |
| 75 kWh | 10h | 6h 45m | 4h 30m |
| 100 kWh | 13h 30m | 9h | 6h |
Read the 7.4 kW column on its own and the answer for most households is obvious. A 50 kWh battery takes under eight hours from empty, which fits comfortably overnight. You do not need more speed than that for a car that sits on a driveway all night.
| 7 kW | 22 kW | |
|---|---|---|
| Supply needed | Suitable single-phase supply | Suitable three-phase supply |
| Typical UK home | Works | Does not run at this speed |
| Overnight charge for a 50 kWh battery | Around 7h 45m from empty | Around 3h from empty |
| Most cars can use it | Yes | No, most cannot |
| Practical ceiling in most homes | Yes | No |
When 22 kW helps
The cases where 22 kW makes sense
They exist. They are just not ordinary homes with one car on a driveway.
A 22 kW charger earns its place where three-phase power already exists and charging time is genuinely constrained. In practice that means a workplace or a shared car park where cars arrive and leave within a couple of hours, a depot with several vehicles turning over quickly, or a home that already has a three-phase supply and a car that can use it.
For a single car parked at home overnight, the extra power buys very little. It shortens the charge from roughly eight hours to roughly three, and then you have eight spare hours the car is not moving. The money is better spent on a charger that can schedule around a cheaper tariff, or on a well-specified installation.
Converting a home to three-phase is a significant electrical project involving your network operator, and it is rarely justified for charging one car overnight. If you are considering a 22 kW unit, establish whether your property already has three-phase supply before anything else.
What this means for you
Before you pay for a faster charger
The most common expensive mistake in home charging is paying for speed that the property or the car cannot use. Checking that first narrows your decision considerably.
- Assume 7 kW. For a single-phase home, which is most of them, anything faster is money spent for nothing.
- Check your car's maximum AC charging rate before buying anything above 7 kW, and check whether that rate is single-phase or three-phase.
- Ask your installer to confirm the phase arrangement as part of the survey. It is a quick question and it settles the speed decision.
- Once speed is settled, decide on the cable arrangement and then the features. Tethered versus untethered covers the first of those, and how to choose a home EV charger puts the whole order together.
Further reading
Sources
- Last reviewed
- Charging electric vehicles — Energy Saving Trust. Published charge times from empty for different battery sizes and charger power levels.
- Electric vehicle chargepoint grant for renters or flat owners: Eligibility — Office for Zero Emission Vehicles, GOV.UK. The list of vehicles eligible for the grant, as published by OZEV.
- Will a home charger work with your car? — EV Charger Help. How the car, the charger and the house each set a limit.