Chargers, power, capacity, efficiency and range

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I thought it might be helpful to explain a bit about the world of electricity, charging, batteries and range.

First, power. Power is measured in Watts or kiloWatts (kW). The key equation to know with electricity is this:

                 Volts x Amps = Watts

In the UK our electricity is supplied at approximately 240 volts. The maximum amperage we are allowed to draw is 30 amps, meaning that from your home, the maximum power you can supply to charge a car is 240 x 30 = 7,200 Watts or 7.2kW - and you need a special charging point to draw the 30 amps. The granny charger plugs in to a normal socket, and we do not draw more than 13 amps from those, so in theory it could draw 3.2kW, but it actually charges at about 2.3kW (for safety reasons I guess). 

Electrical quantity is measured in kW hours (kWh), for example your electricity bill is charged by kWh. Car batteries have a capacity measured in kWh - my car's battery can store 72kWh. 

The range of the car is determined by two things: the size of the battery, and how efficient the car is performing. For example, if my car did 4 miles per kWh, it would run for 288 miles before running out of charge. This is just the same as an internal combustion engine (ICE) car, the range is determined by the size of the tank and how many miles per gallon you get. And in just the same way, the mpkWh of an EV varies with the type of driving just like the mpg of an ICE. But curiously EVS are more efficient around town, and less efficient on the motorway. This is because when you ease off the throttle the car recharges the battery using the kinetic energy of the car as it slows down. Added to this, the performance of the battery degrades in winter, which I have yet to experience. So far, I am getting about 3.5 miles per kWh, meaning the car has a maximum range of 3.5 x 72 = 252 miles. This is what my car's dashboard shows you:



The performance of the car is stunning. Not quite in the Tesla bracket, but the most powerful car I have owned in my life by some distance. But if you get heavy with your right foot, you really see the battery degrading!

Charging times vary according to the power of the charger. To charge my car from empty on the EO home charger takes about 10 hours (72 / 7.2). Out on the road there are chargers up to 350kW! This is where that all important fast charge capability comes in - with one of these superchargers it takes 15 minutes to charge the battery to 80%! The less charge there is in the battery the faster they go, and as the battery fills up it charges more and more slowly. It means that regardless of where you start from, the charge time is more or less the same. The price of charging on the public network also varies, and although it is cheaper than petrol/diesel it is still much cheaper to charge at home. 

I took some pictures of my car charging at an IONITY 350kW charger. Here it is at 45%


See how it is taking 140KW from the charger. And here it is at 85%; see how it is only taking 60kW from the charger.






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