Slow, medium or fast?
Whether you’re new to EVs or an experienced electric driver, it’s a question everyone asks – what the best speed to charge an EV. Whether you’re at home, at work, or on a public charger, if you have a choice of different speeds to charge your EV, which one should you choose. Let’s find out.
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If you haven’t seen it yet, we recommend our previous video which was an introduction to charging. We talked about charge speeds, plug types, and how to use different charging networks. Today we’ll explain more about that first point.
Electric Vehicles come with their own vocabulary, and it’s one of the things that every new buyer learns. But it can be confusing, so let’s simplify it. And for our video today, our imaginary EV has a 50kWh battery. We’ll use that battery size to work out how long our imaginary car will take to charge.
There are three main types of charging speed, Slow, Fast, and Rapid.
And Rapid Charging –Now you may hear the latest rapid chargers being called High Power Chargers, or HPCs. Indeed the hardware manufacturers sometimes label their own chargers as that, but we’ll call them Rapid Chargers.
Let’s start, slowly.
This is the laziest way of all. The household socket. Whether your country uses 120v or 230v AC, plugging into your household sockets is almost like trickle charging an EV, and it’s not recommended for those in a hurry.
For example, at 230v AC you would typically charge at 2.3kW. And whilst every car charges different as the battery fills up, our imaginary EV with a 50kWh battery could take around 22 hours to charge.
So clearly you’ll want to be doing something else whilst you’re slow charging. Like working, or sleeping, a lot. Because it’s going to take a long time.
Other examples of slow charging include lamp-post chargers, which can vary from 3kW to 6kW. And sometimes workplaces or businesses will supply a domestic socket for you to plug in your own charging cable. You may even have been provided one when you bought your car, but they’re easily available from 3rd party sellers. Slow charging cables will most commonly have a domestic plug on one end and box in the middle and a Type 2 socket to plug into your car.
For those who have the time, or only drive a few miles a day, slow charging whilst your car is parked is very common. You might use a two or three pin plug, a Type 2 socket or Commando plug.
One advantage of charging slowly is keeping your battery healthy. Time for a very quick lesson in lithium-ion batteries you find in EVs – as you charge or discharge them, the internal resistance in each cell creates heat. Do it quickly, and there’s a lot of heat. That has the potential to shorten the life of your EV battery, so charging slowly means less heat, and potentially a healthier battery.
However one final point of charging for extended periods with a domestic plug, consistent current over many hours could be a risk. Which is why we recommend a dedicated EV charger installed at home by an accredited professional.
Cost: public slow chargers are commonly free, and workplaces free or subsidized. At home, you might be able to access cheap electricity rates overnight for example, but you won’t take full advantage because you would not get much energy into your car using this method.
Most commonly 7kW, 11kW if you’re using a Tesla Destination charger or 22kW
This is the speed the majority of people use to charge their EVs. And we’re still talking here about AC charging. Your house uses AC, or alternating current. Your EV stores energy in the battery as DC – direct current. So your car has an onboard charger, or converter, to go from AC to DC. And this is where we come across the issue that your car may be the bottleneck. So even if you find a 22kW fast charger, you probably can’t take all that power. In Europe, the Renault Zoe is best known for its ability to charge at 22kW, unlike other EVs.
Many plug-in hybrids and even some Nissan LEAFs only have a 3kW charger built-in, so that’s the maximum they can charge at, regardless of the charger you find. You can still connect them to a fast charger, but they can’t make the most of that power.
Dedicated wallbox chargers at your house would typically be rated around 7kW. But it’s the most common speed of Fast Charger to find at destinations such as shops, car parks, leisure facilities or workplaces. Again most of these are called Untethered, in other words, you better remember to bring your own cable.
Our imaginary EV with a 50kWh battery would charge in around 8 hours at 7kW. Considering most cars spend this amount of time parked at home overnight, or at work during the day, 7kW is considered by many as the ideal speed to charge at.
The charging equipment is affordable, and you’re not waiting a whole day for your car to charge.
And remember too, most people don’t charge from 0% to 100%. So if you need a couple of hours charging whilst you are busy, 7kW Fast Charging is a great option.
Cost: These are often free, and paid for by your workplace or the location owner. For example, to incentivize you to spend time in their shop. And those which do cost money might be cheaper or included as part of your charging plan if you subscribe to certain networks.
And finally, we have Rapid Charging. The type which gets the most attention because you can top up your battery and be driving again in minutes.
These chargers are often found at motorway service stations or on main driving routes. These chargers are also the most expensive for the charging networks to install, both for the hardware the grid connections, so they can be rare in places.
But even though we’re no longer converting from AC to DC, you car might still be the bottleneck. The BMS, or Battery Management System, is in control of the charging sessions and continually telling the charging unit how much power to supply.
50 kW DC Fast Chargers are common around Europe and North America. Not the latest technology anymore, but you can still get an 80% of our example EV in 45 mins. And that should be good enough for most road trip stops, adding another 2-3 hours of driving to the next charger.
And then we get into the very fast speeds of charging – some say Ultra-Rapid, or even High Powered Charging. And of course, Tesla has its Supercharging Network only available to Tesla drivers. On these new, and very fast Rapid Chargers, you wouldn’t typically spend more than 20 mins. That would be enough to go from 20% to 80%, and crucially, take advantage of the fastest speeds. Even the latest electric vehicles seriously slow down charge speeds past 80% state of charge, for battery safety reasons, and so it would be a waste of your time to sit on an Ultra Rapid charger whilst adding the last few kWh of energy. As these chargers are still quite rare, you might also be blocking the charger if you’re charging for an extended period. If you really need a full battery, you would be better moving to a nearby Fast Charger.
It’s also worth noting that whilst modern EVs can keep their batteries cool, relying entirely on rapid charging does have the potential to degrade your battery, and you may find that over time your range decreases, or your car doesn’t charge as fast.
Cost: The cost of Rapid Charging can rise quickly. As you are often charged more for the latest chargers, and billed per kWh, you can often pay a lot more at a Rapid Charger than anywhere else. But they are often in convenient locations and you pay for convenience.
Now tell us your favorite way to charge? Do you prefer to pay extra for the faster charging, or are you happy to charge slowly if you save money? Let us know in the comments below.