In this short series of posts, we'll cover the basics of running an electric vehicle (EV) instead of a petrol or diesel vehicle - an important step in the transition away from fossil fuels. In this post, we'll cover a very misunderstood topic - charging speeds.
We're talking mainly about public charging speeds here because home charging speeds (or more specifically AC charging speeds) are much more straight forward. If a charger says it will deliver 7 kW charging speeds, it generally will deliver that speed for the duration of the charge regardless of other factors. The only exception to this is when a charger is shared between two connectors - so if the 7 kW charger is shared between two connectors, you may only get 3.5 kW speeds if someone is also using the other connector at the same time because the charger is only capable of delivering 7kW in total.
The charging speed graph for AC charging looks something like this:
Public charging
This is where it gets a bit trickier. There are a few key factors involved, some more important than others. But first, the basics:
The rated max speed of the charger itself - (e.g. 50kW, 150kW, 350kW)
The rated max charging speed of the vehicle (e.g. 50kW, 125kW, 350kW)
You will only ever reach the limit of either the car or the charger - so on a 350kW charger, and car capable of only 50kW - you'll only ever get 50kW.
So I'll get 50kW in this scenario then?
In the right circumstances, yes you should do! There are some important factors involved in achieving this - some more important than others. The two most important are:
The state of charge when you start charging (e.g. 20% battery remaining or 80% battery remaining)
The battery temperature (as in the car battery which you are about to charge).
The two above factors are very important for understanding what charging speeds you can expect...
Basically the charging curve for Ultra-rapid charging looks broadly like this:
So if you plug in between 5-40% with your car battery at a good temperature - and you are at a capable charger, you are likely to get somewhere close to the max charging speeds for part of your charge.
You'll note above that I've said part of the charge. The maximum charging speed drops off from about 50% SOC - it's a gradual ramp down but by the time you get to 80-90%, you will see seeing very slow charging speeds. For example, on a car with 150kW capability on a 150kW charger - the flat part of the graph above would that 150kW but by the time you get to 50-60% you are move likely to be seeing 90kW or so slowing gradually to about 40kW at 85%.
Simple...?
Most of the time, it is! Of course, you may not be worried about getting the fastest charge speeds in which case you just plug in and charge and it takes however long it takes. But I think it's still worth knowing that there are also some other factors which can also have an impact on charge speeds:
Outdoor temperature (winter temps generally means lower charging speeds)
Volage compatibility (voltage - e.g. 800v vs 400v)
Shared chargers (multiple plugs per charger)
Load balancing (if all chargers are in use - they may scale down speeds in order not to exceed the max allowance of the area they are in)
Quality of the charger (some brands are better than others as with anything!)
Now I know what you thinking - that's a lot to think about and yes, yes it is! But to be honest, there isn't much you can actually do about any of these additional factors - but they are worth knowing in case you don't always get the charging speeds you expect.
The executive summary is basically:
Your maximum charge speed is achievable but you won't get it every time or for the whole duration of your charge - but there are things you can do to improve your charging speeds more generaly...
Arrive at Ultra-Rapid chargers with a low state of charge - ideally between 5-20% battery.
Try to stop at chargers with multiple chargers (e.g. 8 chargers rather than somewhere with 1 charger) to increase your chance of getting a free charger.
Expect to stop for slightly longer when it's very cold (and/or your battery is cold)
Try to park 1 car away from cars already charging (in case power is shared across chargers). Many newer chargers however don't share power so this is often not necessary (or possible).
Avoid charging above 80% on Ultra-Rapid chargers - it's almost always quicker to go and then stop again for a short time at another charger rather than charge to 100%. As the graph earlier shows, charge speeds massively reduce above 80%.
Try and charge immediately after having driven rather than after you have stopped.
Happy charging!
If you have any thoughts, feedback or ideas you wish to contribute on this or any other topic covered by The Climate Coach - please get in touch, we'd love to hear from you.
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