‘Charging speed?” is a common question among new and potential electric vehicle (EV) customers — and for very good reason. Vehicles are there to be driven and with empty petrol tanks taking just a few minutes to fill to the brim, nobody wants to hear the horror stories about it taking more than 35 hours to fully charge an empty EV. However, in certain cases that can be a fact.
There are a combination of factors that dictate the time you will spend recharging your EV.
These include the speed of the charger, the maximum supported charging speed of the EV itself, the vehicle’s battery capacity and even how empty that battery is.
These factors may seem rather daunting at first, but a fossil-fuelled vehicle can be used as a great comparison. The size of the fuel tank (battery capacity) dictates how much fuel (energy) is required to fill. The speed/power of the pump (EV charger) dictates the potential rate of flow, but this can vary due to the size of filler nozzle (or maximum supported charging speed of the EV) and lastly, filling the tank to the brim often causes the pump to click off, slowing the rate; the same applies with an EV, the closer to 100 per cent you get, the slower the charging speed.
When it comes to EV charging systems there are two types, direct current (DC) or alternating current (AC). However, regardless of their size and capacity (which generally equates to range and/or performance), EV batteries store electricity as DC. With DC charging, energy is fed directly from the charging station into the vehicle’s battery, which means that DC chargers will charge a vehicle the fastest, but that doesn’t necessarily make them the best or most common way to charge.
DC chargers, also known as Mode 4 or rapid/public chargers, can often be found in publicly accessible places across New Zealand and vary in output speed, and costs. From power company-supported free stations whose 25-50kW chargers offer around 150km/hour (80 per cent in 1.5 hours) or 300km/hour (80 per cent capacity in an hour) respectively, based on a vehicle with a 64kWh battery. There is also an increasing network of Ultra Rapid Chargers 175kW-300kW that charge up to 1000km/hour or 80 per cent in a mere 15 minutes.
It’s worth noting that public DC charging time is recorded as the time to reach 80 per cent, because the charging rate usually decreases significantly towards the end of the charge. It’s also deemed better for the battery to only charge to 80 per cent and considered good etiquette if there are others waiting to use the public charger.
DC station charging speeds are evidently impressive, but due to their higher energy costs and availability, are more suited to taking extended EV trips across the country.
Then there are AC chargers, which are used for a majority of charging (often in the home environment). Most EVs come with an 8amp portable car charger (Mode 2 or trickle charger). These plug-in units use a household socket and produce the lowest charging speeds, essentially producing 1.8kW, so 10km/hour and a full charge in 35 hours. Portable chargers are helpful in a pinch but generally not recommended for everyday use as they rely on the integrity of the wiring in your home, which is not always suited for the high-power demands that are typical of modern EVs over a long period of time.
Offering an increased charging speed, fixed AC chargers (Mode 3) can range from 3.7kW to 22kW three-phase, with single phase 7.4kW being the most common in NZ. Single-phase 7.4kW chargers produce up to 4x faster charging speeds than a portable charger, around 40km/hour (fully charged in nine hours based on that same 64kWh battery). If “smart” they can also best utilise lower energy/solar energy rates, while still fully charging overnight.
Three-phase 22kW chargers have the capacity to achieve even faster speeds of 120km/hour (fully charged in three hours), however, it is important to understand that AC charging requires the car to convert the AC to DC before being stored in the EV’s battery. Therefore, when charging from an AC charger, the charging speed is constrained by the size of a car’s onboard charger, even though the AC charger may be capable of a faster charging speed.
As an example, you may have a three-phase 22kW AC home charger installed, but if your EV can only convert a maximum of 6.6kW on a single phase via the onboard charger, the highest charging speed you will see is 6.6kW. Although it may seem unnecessary to install an EV charger with a higher capacity than your vehicle supports, it makes sense to upgrade for potential safety features, smart charging options, and future-proofing purposes.
“Fast AC charging at home is the perfect way to completely replenish your daily commute during cheaper off-peak rates, or fill up a long-range car battery during overnight parking periods,” says Tom Rose, product owner of specialist company Evnex.
Right now, EV charging speeds are still lagging behind the time spent at traditional petrol pumps, but when you take into account the ease, cost savings, clean energy sourcing, and the fact that you can charge overnight from the comfort of your own home, maybe a trip to the gas station isn’t that convenient after all.