Charging Your EV
By Chris Gilbert
Charging the Kona at Lochee Charging Hub in Dundee
Having had our first Electric Vehicle for a little over a year, we’ve made a few long journeys that require the use of public chargers. These are some of the experiences I’ve had and some of the things we learnt along the way.
Connectors
Most modern EVs have two connectors. This is what they look like.
DC or “rapid charge” connector
This will be CCS or CHAdeMO.
You will have one or the other.
AC or “fast charge” connector - usually a “Type 2/Mennekes” connector. This also where the top part of the CCS combo connector fits.
This is the connector you will use at home, and at slower public chargers.
What’s a kW? What’s the Difference Between a kW and a kWh?
This isn’t necessarily easy to understand, and it is quite important. A kilowatt (kW) is a measurement of energy use. A thirsty appliance like a kettle would use 2-3kW.
A kilowatt-hour (kWh) is a measurement of energy use and time. So, your kettle might use 2-3 kW, but it would only use it for a few minutes. EV chargers use large amounts of power continuously, and require a particularly large power draw because of that.
EV batteries are measured in kilowatt hours (kWh). Our Kona battery is 64 kWh, meaning it could produce 1kW of output for 64 hours. How much power you actually use though will depend both on how efficient your car is, and how efficiently you drive.
A typical Nissan Leaf battery is 24 or 30 kWh. This battery size largely determines the range of your car, between charges. The bigger, the better.
Home Charging
At home where you will likely do most of your charging, you will charge on the AC connector, usually at about 7kW. Typically this would add 20-30 miles of range, per hour of charging. So if you charged for 1 hour, at a rate of 7kW, you would add 7kWh to your battery. Get it?
To charge our car with a 64kWh battery from 0-100% takes around 10.5 hours. Usually we just keep it topped up though, and rarely charge much each night.
You should take advantage of Economy 7 or time-of-use electricity tariffs to charge it at the cheapest possible time. All EVs have settings to choose the charging time you want.
The speed of charge will also depend on whether you have a wall-box fitted or charge on a 3 pin plug. I strongly recommend getting a wall-box fitted. They are around £300 with the OLEV grant, and charge the car much faster and more safely than a standard plug.
We got a PodPoint fitted, though lots of options are available, and the Zappi is definitely worth a look for people with Solar panels.
A Note On 3 Pin Plug Charging
You can plug in and charge on a standard 3 pin UK plug. It’s incredibly useful. It’s also incredibly slow. So use it as a “granny” charger (as they are nicknamed). Plug in at friends and relatives houses, or when there isn’t a rapid charger nearby.
Our Kona takes 35 hours to charge 0-100% this way! So it’s really not a great strategy if you are in a rush. But everyone has a plug socket. You will use it.
If you do need to do this regularly, I recommend you buy a very high quality, IP66 (water and dust proof) extension lead. Something like this from Tough Leads.
The cable that comes with the car won’t be long enough, and you shouldn’t just buy an off the shelf extension - they aren’t designed for the many hours of constant usage that an EV required, nor waterproof. I’d also recommend buying a basic socket tester to make sure you aren’t plugging into anything dangerous.
Fast vs Rapid Charging
Usually the AC connector is what you use for so called “fast” charging, or charging at home, but is not the fastest way to charge! For most cars, you could charge at a maximum of 22kW with this charger. On a long trip, you will be waiting around for a long time to charge this way.
Instead, you should be searching for rapid chargers.
Rapid or Ultra rapid charging is what you will want to use when taking a stop on a long trip. For that, it’s the CCS Combo or CHAdeMO connector that you will need.
Most new cars now use the CCS connector (though the Nissan Leaf uses CHAdeMO).
Rapid charging is usually 40-50kW, and ultra rapid is anything faster than that, currently at up to 250kW (Tesla/Porsche) or even faster in the near future.
You can find out the maximum charging speed of your model from EV database.
At a typical 50kW, you’ll be adding about 150-200 miles of range per hour of charging. So a lunch break is enough to set you on your way for another 2 or 3 hours of driving.
The “combo” part of the CCS combo connector comes from the fact that both top part and the bottom part of the socket in your car are used. When charging at home you only need to use the top (AC) part of the socket.
Side note: Older Renault Zoe cars only have the AC/Type 2 connector, and can rapid charge on the single connector. This is unusual though - mostly you will want to use the CCS or CHAdeMO connector.
Charging Speed and Range
The time your car takes to charge depends largely on the car, and battery size. One helpful calculation you can use is the average energy use for your car, so you know how many miles you can get with the juice you have. Check the EV Database here for those figures - it’s an excellent source of data.
Our Kona has averaged 4 miles per kW over a year or so of usage. However, this is very much dependent on a the trip you are doing and time of year. I would estimate a range of 3.5 miles per kW on a long motorway trip. This could also be written as 285 watt hours per mile (Wh/m) - given by 1000 watts / 3.5 miles.
Here’s some rough rules of thumb:
- 10 kWh = 35 miles range.
- 30 kWh battery (Nissan Leaf) = 105 miles motorway range (guesstimate).
- 64 kWh battery (Kona Premium) = 224 miles motorway range (fairly accurate).
We have a 64kWh battery, so we usually plan to stop every 200 miles or so. We can then push further or stop sooner as required by the route and battery level.
Cross country A roads are better, as is driving in the inside lane of the motorway.
Speeds above 60 mph will use the battery power faster, and city speeds will only sip the juice very slowly.
The ideal long range efficiency vs speed ratio is the same as for petrol vehicles - around 55-60mph. This is why cross country A roads are ideal for EV driving efficiency.
The 20-80 Rule
The fastest charging occurs between a 20-80% state-of-charge on the battery. As such, to minimize time on charging stops, you can plan to keep the battery between these levels during your charge stops.
If you are pressed for time, just charge up to 80%, and continue on to the next charger. If you have more time, it doesn’t hurt to let the car charge more, but it will get slower and slower at charging, the closer to 100% you get.
Usually I set the car to charge up to 90 or 100%, and allow it to charge more if we have time. If we come back to the car before it’s reached 90% then we can leave early or not, depending on how we feel at the time.
Waiting for the last 10% is usually slow, so we don’t bother.
When To Unplug
I have a helpful tip for you here. Check the Fastned database on your car - click “Can I fast charge my car”, then choose your vehicle. Next click “Charging tips for this model”. You will find a wealth of information, including a charging time graph.
These are different for each car, because they are software controlled.
A typical charge prediction on our Kona on a rapid charger in Edinburgh, was from 10-80% - predicted to take 1 hour 7m.
A typical charge rate at this charger and time was 38kW. It could be quicker or slower depending on the charger and battery temperature. As such, just having a car that is capable of charging at 150kW doesn’t mean it’s going to pull 150kW from the charger at all times!
Planning Your Route
When you are going on a long trip in an EV, planning is important. You should look at the range of your car, and the distance you are planning to travel, and how long/where you will need to charge on the way. The best way to do this is to plan to stop for meals or toilet breaks at the same time as you charge, so you are not sitting around waiting.
ZapMap is the best app I’ve found for finding chargers and for route planning. The interface is not perfect and could use some UI improvements, but the power of the app is excellent. It can tell you when charge points are occupied or available, and allows users to report problems.
I use it extensively, when in and out of the car to plan journeys. ZapMap can also help with the 20-80 rule I mentioned earlier - it will optimise charging stops to try to use this rule of thumb.
There are also alternatives like Plugshare, which I also like, but ZapMap is general more extensive for the UK and widely used in this country.
The only missing feature I find with these is they don’t yet work with Apple Carplay or Android Auto.
Each network often has their own app too, but they usually only show their own chargers. This isn’t very helpful really, since individual networks don’t achieve ideal coverage across the UK at the moment.
Recent versions of Google Maps also show charging locations! We usually use Google Maps for navigation, so this very useful. They also show availability where they have this data, but don’t have the social features and fault reporting features that ZapMap and Plugshare offer. I use a combination of Zap-Map to find the chargers, and then Google Maps to navigate via them.