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How and when drivers charge

How, when and where drivers charge their electric vehicles will depend on:

  • if they can charge at home or work;
  • the vehicle’s battery size;
  • how far the driver wants to travel in their electric vehicle;
  • the location and availability of charging stations when travelling; and
  • whether the vehicle has a secondary energy source, as with plug-in hybrid electric vehicles (PHEVs)(external link).

Following overseas market trends, the majority of charging in New Zealand is carried out at home and at night, with some PHEV owners only ever charging at home.

Therefore, public charging infrastructure should:

  1. provide for those travelling longer distances; or
  2. be an alternative to home charging, if it is not available or if the ­­vehicle is stored away from home. 

The act of charging

The driver parks the electric vehicle so the supply cable can reach between the charging station and the vehicle’s charging inlet, in most cases there will be a marked parking zone.

DC charging

For DC charging, a tethered supply cable is provided on the charging station. The driver or charging station operator selects the compatible supply cable and connector from the charging station and connects this to the electric vehicle inlet. The driver may then need to activate the power supply by using a start button on the charging station, radio-frequency identification (RFID) tag, swipe card, smart phone app or other device. Charging will start once access has been accepted and communication between the vehicle and the charger is established.

AC charging

For AC charging where a socket outlet is provided on the charging station, the driver provides the supply cable.

The driver plugs the supply cable into the charger’s outlet socket before connecting it to the electric vehicle inlet. Access may need to be activated. Charging will start once communication between the vehicle and the charger is established.

Note: The driver or charging station operator should ensure they minimise all trip hazards that could be caused by the supply cable.

The electric vehicle’s charging system

The electric vehicle’s charging system  includes:

  • the charging station (including its safety components) and
    • the vehicle’s on-board charging components)
    • the electric vehicle’s battery.

The charging station

There are two different charging systems for charging electric vehicles – Direct Current (DC) or Alternating Current (AC). Batteries store electricity as DC; however electricity is moved around the local electricity network using AC.

DC charging: a DC charging station converts AC power to DC. DC power is then passed to the vehicle and stored in the battery. 

AC charging: an AC charging station supplies AC power from the grid to the vehicle. The on board system converts the AC power to DC and it is then stored in the battery.

The vehicle

Most electric vehicles have an on-board AC to DC convertor that allows the vehicle to be charged from the local AC electricity supply; some vehicles also have DC inlets.  

AC inlet only

Some plug-in hybrids, such as the Audi A3, only have AC inlets. 

Dual inlets

Some vehicles have two separate inlets to enable both AC and DC direct power supply; for example the Nissan LEAF has a standard AC power using a Type 1 inlet for standard AC power and a CHAdeMO inlet for high voltage DC.

Combo inlets

Some vehicles have a combination inlet, such as the BMWi3, where the AC inlet is combined with DC pins, so the type of charge is dependent on the type of connector.

Communications

The majority of electrical vehicle charging systems are set up so that active communication is required between the charger and the vehicle before charging can commence. If that communication is interrupted, charging will cease. In most vehicle models, the connector at the vehicle end will be securely locked in place when the vehicle is locked.

How much ‘charge’ is needed?

Overview

Typically, PHEVs have smaller battery packs because they have more than one energy source, whereas battery electric vehicles (BEVs) are completely reliant on the battery for motive power so require a much larger battery. The battery size, or capacity, will determine the amount of charge required to fill the battery, while varying factors, outlined below, will determine the rate of charge.

Battery capacity

The battery range of some PHEVs is as little as 30km, while most mainstream BEVs have a range of 100km to 200km; Tesla models currently have the greatest battery range, exceeding 300km.

Refer to the Ministry of Transport's website(external link) for an up-to-date view of New Zealand’s current EV fleet.

Indicative battery sizes are below:

Make and model Battery (kWh)
Nissan Leaf 24 or 30
Tesla Model S 60 or 100
Mitsubishi iMiev 16
Nissan e-NV200 24
Renault Kangoo 22
Tesla Model X 100
Renault Zoe 22
VW e-Golf 24
Tesla Model 3 TBC
Mitsubishi Outlander 12
BMWi3 22 or 33

From an infrastructure standpoint, it is important to note that battery costs are expected to decrease over time and motor vehicle manufacturers are likely to increase the size of batteries. This means more kWh will be required to charge vehicles from empty to full although drivers will need to fill-up less often.

Factors affecting the rate of charge

The amount of time needed to completely charge an electric vehicle depends on several factors, including:

  • battery capacity;
  • ambient temperature;
  • utility/ grid constraints limiting the current available to the charging station;
  • temperature of the charging station;
  • charging type;
  • the vehicle’s battery management system (BMS);
  • the capability of the on-board charger; and
  • the amperage of the charging station.

The amount of charge already in the battery also affects the speed at which a battery can recharge – the closer it is to empty, the faster the electricity can flow.

When a battery is charged to 80 percent the charging rate typically starts to taper off. Therefore, if a driver is paying by the minute at a fast charge station, it can become costly to charge over 80 percent and they may not wish to completely fill up.

Rate of charge

Charging rate terminology

Slow, fast and rapid charging are terms used to describe relative rates of charge supplied to an electric vehicle and reflect the capability of the charging socket or station. 

An outline of charging rate terms is provided below, noting that the definitions continue to shift as the technology advances.

Term Description Charge capability
(kW) and charge rate (km/30mins)
Trickle charge This is used to describe a charging rate that may take up to eight hours to charge an electric vehicle.
Overnight charging at home using a Mode 2 power supply is an example of trickle charge.
3kW
~8km/30 mins
Slow charge This typically describes a Mode 3 (AC) power supply that may take up to eight hours to fully charge an electric vehicle.
Slow charge infrastructure is suitable for ‘electrified parking’ or overnight facilities.
~7kW
~20km/30mins
Medium charge This typically describes a Mode 3 (AC) power supply that may take up to four hours to fully charge an electric vehicle. ~22kW
~40km/30mins
Fast charge This typically describes AC charging systems (Mode 3) that have been enhanced to enable faster AC charging suitable for on-the-move charging. >43kW
~80km/30mins
Rapid charge This typically describes Mode 4 (DC) charging systems and is the fastest charging option currently available in New Zealand, delivering up to 50kW.  >50kW
~100km/30mins
Supercharging Supercharging is used to describe Tesla proprietary high-speed charging option. ~170km/30mins

 

What is the minimum rate to be called ‘fast charge’?

It is recommended that the term ‘fast charge’ is reserved for charging stations that have an output of at least 43kW. At this rate that a driver could reasonably fill-up from empty in under an hour.