An EV will need its battery recharged, in a similar way to your smartphone. There is some specific terminology and methods to be aware of when talking about charging an EV. We discuss these below and offer some comparisons between vehicles and the rate at which capacity can be added to the battery. As a useful reference we will use the Miles added per hour, (MPH) measure, for example 30MPH means 30 miles of range added to the battery when charged for an hour.
DC Rapid Chargers
We mentioned the high voltage direct current battery pack that powers an EV in a previous article. The quickest way to recharge an EV battery is by connecting a high voltage direct current charger to the battery. These are known as Rapid Chargers and are specially designed units that deliver power rapidly, the power delivery of these units usually range from 50kW to 350kW and can take a vehicle’s battery from 20-80% full in 30 minutes, depending on the vehicle.
The Rapid charger will not deliver more power than the car is capable of managing so a vehicle with a 50kW capable charging circuit will derive no benefit from using a 150kW charger. Since these charging units need a suitable electrical supply from the grid and the cost of the charging hardware the installation costs typically range between £20,000 and £40,000, they are not something you will install at home or work.
These chargers are typically sited at key points on main routes to provide in-journey charging. They can be found on existing service station forecourts or other strategic locations. These are not meant to be places to park your vehicle whilst off shopping for a few hours.
There are multiple options when charging your car from an alternating current power supply. Each has different charging characteristics which we discuss below.
Although often referred to as a ‘charger’, whatever AC power source you plug your vehicle into, the actual charger is inside the car. To follow the official terminology, what most people install at home is an EVSE, Electric Vehicle Service Equipment unit. These units communicate with the car to establish a safe connection and then turn on the power to the charge controller and inverter unit built into the vehicle. When the vehicle has had sufficient charge it tells the EVSE to turn off the power. The rate of charge will be determined by the vehicle’s capacity and the connection rating of the EVSE.
If you have a 3 phase supply you can install an EVSE capable of delivering 22kW. Since most homes do not have this type of supply, these units are more commonly found at commercial installs and at public charging locations.
Installing a proper charging point at home will speed things up. A typical home installation will tap into the meter tails that connect to the consumer unit. A standalone consumer unit fitted with a special trip switch and a suitably rated cable is run to the EVSE unit. The standard Nissan Leaf was fitted with a 3.6kW charger and a 7.2kW unit was available as an option upgrade for £1,000. The majority of vehicles today have a minimum 7.2kW on board charger. If you installed a 3.6kW EVSE and plug in a car capable of charging at 7.2kW it will be limited to a 3.6kW charging capacity. It makes sense to install the highest capacity possible where the electrical connection and budgets permit.The table below shows the AC charging rate of 2 cars with 7.2kW chargers, which are capable of adding 23-25 miles of range per hour, if plugged into a 3.6kW EVSE, then the rate of charging is halved, adding 11-13 miles of range per hour. Domestic connections will have a maximum of 7.2kW unless you have a 3 phase supply.
Plugging into a standard 13A home socket is the lowest cost basic option. You will need an appropriate adapter cable that connects to the vehicle and the standard socket (also known as a Granny Charger). These adapters have a control unit built into them that limits the power that can be consumed by the vehicle and are normally included with each new car. These typically limit the load on the circuit to less than 10 Amps. This is a safety precaution designed to prevent overloading of the domestic wiring circuit. This is the slowest way to charge a vehicle and it provides a trickle charge.