How Can I Charge My Electric Car? – Part 1 – Electricity

I have an electric car. Sure it is different from a petrol or diesel ICE (Internal Combustion Engine) but it is a lot simpler. In a typical ICE there are hundreds of moving parts that all require oil to lubricate and water to keep cool. They wear out too and require regular maintenance and repair. Then there is the petrol vs diesel thing. Every time I go in to a petrol station I am nervous that I will pump in the wrong fuel… and yes, I have done it!

So, with an electric car fueling it is easy isn’t it? You plug it in and charge it up… just like a laptop? Well, in theory that is true and at its simplest level that is exactly all you need to do but electric cars are not laptops, they move around and need charging both at home and when on trips. There are many manufacturers and they haven’t yet fully agreed on a standard for charging electric cars. There is also the complication of the electricity itself… talk of kilowatts, kilowatt hours, amps and volts. Nope, it is not simpler than an ICE, it is a lot more complicated.

What I want to do with this series of posts is to try to clarify for the beginner what charging options currently exist for the electric vehicle owner. As I said, it is a complicated area and although I will try to cover everything please recognise that this is a moving target and by the time you read it the goalposts may have moved… considerably! Let me know if there is anything wrong or out of date by posting a comment below and I will address it.

Electricity… is it all the same?

As you know, with an ICE there are several types of fuel… petrol, diesel and LPG are the main ones. So, whatever type of fuel your car uses you must stick to that fuel. However, there are different grades of each fuel and you can choose which grade depending on the performance and price you are after. Apart from that you need to know nothing about the fuel itself. You fill your tank and away you go.

Unfortunately, with electric cars you must know a little bit about the electricity. It becomes important because electricity is not as simple as petrol or diesel and to charge an electric car you will need to understand where and how you can do it and do it safely and that requires a bit more detail than just “petrol or diesel”. There is no getting away from it… sorry.

So, let’s get stuck in with some details on what we need to know about electricity first…

With electricity there is only one type. It is called electricity!!! However, electricity is complicated and that is why charging an electric car is complicated. Well, that statement is only partly true in that the physical act of charging is easy… you plug it in to an electricity source with some kind of lead and it charges. However, electricity has many variables the main ones of which are volts and amps.

Although it isn’t exactly the same a useful analogy is to compare electricity with a water supply. With a water supply there are also 2 main variables… the size of the pipe and the pressure. With water, the bigger the pipe the more water you can get per second but that also depends on the pressure in the pipe… the higher the pressure the more water you get per second. From this it means then that to get more water per second out of the tap we can either increase the pressure or the size of the pipe…. or both. Increasing the size of the pipe is easy with water… we open the tap but the water pressure is pretty constant at “mains pressure”. We cannot vary the pressure. The water company regulate and maintain that for us and for our purposes it is constant.

So it is similar with electricity… think of the size of the pipe as amps and the pressure as volts. This is not actually the case at all but comparing it to a water system in this way does give us an easier way to think of it.

So, the higher the volts the more electricity we get per second and also the higher the amps the more electricity we get per second. In fact, with electricity we use “per hour” as the standard measurement.

We measure how fast the electricity can be delivered in kilowatts (kW or 1000 watts). You will have seen that used when looking at electrical equipment… it is the same. When looking at a bit of electrical equipment the kW is the power of the device. Or to put it another way, it is a measure of how fast the device uses electricity. A kettle might be rated at a power of 3kW or 3000W. That means it needs to be plugged in to a socket that can deliver electricity at the rate of 3kW.

Now this is where we need to talk maths… don’t be scared. I will talk you through it if maths is not your thing. I would like to avoid maths altogether… we don’t need maths when filling our petrol car do we. No we don’t, but it is simply unavoidable if you want to understand charging an electric car.

Let’s consider that 3kW kettle. We have said that the amount of electricity being delivered, or power,  varies depending on the volts and the amps. Well, in the UK the mains (or grid) voltage is 230V. Like the water pressure in the water system the volts do change from minute to minute within an accepted range but for our purposes we can consider volts to be constant at 230V. So, with volts and amps being the two ways to vary the electrical power and with the volts constant, if we want to vary the power the only way is to vary the amps. So, our 3Kw (or 3000W) kettle needs 230V and 13A. 230V x 13A = 2990W – close enough.

If your maths isn’t as good as you would like then just remember these rules:

  • If you know the volts and amps you can calculate the power like this:
    Power in watts is volts multiplied by amps or W = V x A
     
  • If you know the volts and power you can calculate the amps like this:
    Amps is power divided by volts or A = W / V

So, going back to our kettle… it has a power of 3000W. We know that the grid voltage is a constant 230V so we can calculate the amps using the rule above as:

Amps = 3000W / 230V and this is about 12.5A

That is why you need a 13A fuse in the plug. The fuse will blow over 13A because a normal household socket can only cope with 13A. You can see that 12.5A is very close to the limit but that is OK because it is only on for a short time.

When you get close to the limit of an electrical circuit it usually starts to get warm or even hot. The closer to the limit it gets or the longer it is near the limit the hotter it gets. This will become very important later when we talk about where is is safe to charge your electric car.

This then is pretty much all the maths you need to understand electric car charging. Yes, to those in the know, I accept that this is not 100% accurate but I am not trying to teach physics GCSE here… just to get over the minimum of what some one must know to be able to know where and how they can charge their electric car when out and about.

So why do you need to know all this complicated stuff? surely you can just plug in your car anywhere there is a socket and charge? Why does it have to be this complicated?

The answer to that is mainly because cables need to be thicker to carry more power and fuses need to be able to cope with greater power but not so big that they don’t blow if there is a problem. We don’t need to go into the detail but it is important to remember when charging an electric car that you must always use cables that can safely cope with the power the car is taking from the grid.

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