A 7 kW charger is generally single phase and a 22 kW charger is three phase. The faster one only helps if your car can accept that power and your property's supply can deliver it. For many households a 7 kW charger covers overnight charging, but your car and electrician should confirm.
If you are choosing a home EV charger, "7 kW or 22 kW?" is one of the first questions that comes up. Bigger sounds better, but with chargers the faster option only helps if the rest of the chain can keep up. That chain is your car, your property's electrical supply and how you actually use the vehicle.
What the numbers mean
The "kW" figure is how much power the charger can deliver at its maximum. More power means more energy going into the battery each hour. As an illustration only, a charger delivering 7 kW can add up to about 7 kWh to a battery in an hour, and one delivering 22 kW up to about 22 kWh. Real charging often runs below the maximum, and batteries usually slow down as they fill.
In general:
- 7 kW chargers are single phase units, typically on a 32 amp circuit.
- 22 kW chargers are three phase units, typically also at 32 amps per phase.
The difference between single and three phase is about how your property is supplied with electricity, and that is something your electrician can check.
First limit: your car
The charger does not push power into the car. The car's own onboard charger decides how much AC power it will accept. Many EVs accept 7 kW and some accept more, while only some accept 22 kW. If your car tops out at a lower figure, a 22 kW charger will still only deliver what the car allows.
So before you buy, check your vehicle's specifications or manual for its maximum AC charging rate. If you are likely to change cars, think about what your next one might accept, but do not assume a future vehicle will.
This is separate from public DC fast charging, which works differently and bypasses the car's onboard AC charger.
Second limit: your property
Your home needs to be able to supply the charger safely. Things your electrician will look at include:
- Whether you have a single phase or three phase supply. Many residential properties are single phase. Switching to three phase is not a small job and is not always practical.
- The capacity of your incoming supply and switchboard. The EWRB says that for chargers above 15 amps, the installer must make sure the incoming mains will not be overloaded, and that maximum demand and voltage drop are checked.
- Everything else drawing power. The charger shares your supply with cooking, hot water, heating and anything else running at the same time.
- The distance to the charger location. Longer cable runs need to be considered for voltage drop.
If the supply is not up to it, one option is a charger that moderates its charging rate. The EWRB says that asking the household to manage load by switching a charger on and off is not an acceptable way to deal with limited capacity.
Do you actually need the speed?
A useful way to think about it is how much charge you need to add and how long you have. Work out roughly how much energy you use on a normal day, then check how long the car is parked at home.
- If you drive a modest distance each day and the car sits at home overnight, a lower power charger may cover your needs comfortably.
- If you have a large battery, drive long distances most days, or have several vehicles sharing one charger, more power may make a real difference.
- If you only need to top up now and then, the slowest option may be plenty.
For many households a 7 kW single phase charger suits overnight charging. But the only way to know is to match it to your car, your driving and your property.
Questions to ask before you buy
- What is the maximum AC charging rate of my car?
- Is my property single phase or three phase?
- Can my supply and switchboard handle the charger I want, and what would be needed if not?
- Does the charger have load management, and do I need it?
- Do I have a Supplier Declaration of Conformity for the charger? WorkSafe suggests asking for one and giving it to your electrician to review.
Safety and who installs it
WorkSafe says a wall-mounted charging unit at home must be installed by a registered electrician, so whichever size you choose, the supply and protection side of the job is theirs to assess and sign off.
If you would like help matching a charger to your car and home, talk to Honest Electrical about EV charger installation. We will look at what your property can support and recommend what makes sense, rather than selling you more than you need. We install chargers as an Evnex Installation Partner, and we will talk through the options with you.