APPENDIX 1: Supplementary technical notes

Electric vehicle charging rates

The charging rate for electric vehicle charging is determined by the lowest capacity of:

  • the car (on board AC/DC converter for AC or maximum DC charge rate for DC set by battery size and chemistry);
  • the power supply (AC from the mains or DC rectified on a fixed charger); and
  • the cable from the power supply to the car.

Most cars have on-board AC/DC converters from 3.5 kW (single phase) to 22 kW (3 phase). These limit AC charge rates for the vehicle regardless of AC power source or cable size.

Home charging

Electric vehicle home charging is typically AC:

  • from 2.5 kW (single phase, 10 A delivering about 12 km driving range per hour of charge)
  • up to 22 kW (32 A three phase delivering about 100 km driving range per hour of charge)
  • but commonly 7 kW (32 A single phase, 35 km range per hour)

Destination charging

Destination chargers with 22 kW AC, three phase; these chargers deliver the maximum capacity most electric vehicles can currently accept. Sites with only single phase supply or limited power capacity may offer less, but still supply the maximum 7 kW AC charge rate for many vehicles.

DC fast charging

Most electric vehicles have a limited AC charging capacity but can charge faster using DC (some models, particularly Plug-in Hybrid Electric Vehicles (PHEVs), lack DC charging capabilities). DC charging can be at any power level from 1 kW to up to 1,000 kW or more. It can overcome AC charge rate limits, so is often called DC Fast Charge.

Even for DC charging, electric vehicle batteries have a maximum charge rate that slows as the battery fills. This rate slows markedly above 80 per cent state of charge. Current model electric vehicles have peak charge rates of 40-110 kW.

The cost of installing more powerful chargers is much higher than lower power chargers, as higher-powered chargers often need expensive upgrades to the power supply. The first generation of DC fast chargers were mostly 50 kW (4 km/min of charge, peak), with the exception of Tesla superchargers which provide up to 110 kW (9 km/min of charge, peak).

New model electric vehicles have been announced with higher peak charge rates. Trucks and buses, with much larger batteries, also can accept higher charge rates, up to 700 kW (55 km/min of charge) with even faster rates proposed. Charge rates more than about 175 kW require charging cables to be cooled to avoid overheating (or instead use very thick cables which are heavy).

Electric vehicle driving range and charger spacing

Determining the correct distance between chargers depends on the kilometre range of electric vehicles, when they have a full battery. Many first generation electric vehicles have ranges under 150 km, which shortens at high speed, going uphill, driving into the wind, in cold weather and as the battery ages. While suitable for urban use, these first generation electric vehicles are impractical for long journeys.

Newer electric vehicles have larger batteries and longer ranges, mostly between 200 km and 500 km. A 200 km range allows for two hours of driving before stopping to recharge. A distance between chargers of no more than 150 km means that a charge to 80 per cent capacity will allow a 200 km range electric vehicle to drive to the next charger. Shorter distances between chargers would allow for side trips, adverse conditions, battery ageing, as well as provide greater convenience.

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