ABCs Of EVs: Alternating Current

Here's everything you need to know about alternating current (AC).

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InsideEVs Editorial Team

By: InsideEVs Editorial Team

Mar 12, 2021 at 12:31pm ET

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The world of electric vehicles can sometimes seem like it comes with its own vocabulary, and that's where we come in. Look out for our ABC of EVs series, to demystify the words and phrases you'll hear.

If you haven’t checked out our previous video on Direct Current, we’ll put a link to that in the Notes below. In that video, we explained how direct current is used to charge and how it’s stored in a battery.

Today it’s the turn of AC – welcome to the ABC of EVs – A for Alternating Current. And if you like this video remember to hit subscribe to never miss a show.

AC power, or Alternating Current, is the type of electricity available on power grids. You might ask why power grids don’t use DC? Because it’s much more efficient to transmit power of long distances, all around the country, using very high voltages. This overcomes the loses due to resistance. And Alternating Current, unlike DC, is also able to use transformers. So that means the high voltage power can be stepped down to something much more useful in our homes, once it reaches our local area.

And why is it called Alternating Current? The direction of the current changes many times per second. In the UK the direction changes every 1/50th of a second. We use the work hertz to describe that. In the US for example the grid is 60hz, or 60 cycles per second.

So how does this apply to EVs?

Firstly let’s talk about motors. In EVs, they’re AC motors. The motor is assembled of a stator that forms the outer part, and inside it is a rotor that spins. Inside, magnets. They make the rotor turn inside int the stator producing torque.

But how to make magnets move? Your car uses alternating current on those electromagnets to create a constantly moving North and South pole. The alternating current is creating that magnetic field to turn the motor.

Let’s talk about AC charging. Despite your car storing energy as DC, AC charging is the most common way of charging an EV. The power from the grid is sent into your car, and an inverter changes it to DC power for the battery to store. You’ll see it referred to as the speed of the On-Board Charger, expressed in Kilowatts. Although it’s not so much a charger but a converter.

The two factors affecting charge speed are 1) the power of the charge point and 2) your cars ability to covert the power.

AC chargers range from around 16 amps to 63 amps. That’s equivalent to charging at 3.7kW speed to 43kW.

AC charging posts don’t require any special technology to transform the power they’re getting from the grid, so the chargers are often cheaper to produce. And they can often be free to use for consumers as well.

And you know we talked about inverters? Well, the motor in your EV runs off AC power. When you put your foot on the throttle, what you’re actually doing is changing the frequency of the current to change the motor speed, and the amplitude of the signal to change the motor’s torque.

What do you think?

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If you’re familiar with piston cars you’ll know that an alternator is a part that requires replacement at times. When you slow down in an EV, your motor actually becomes an alternator. It produces power and sends it back into the battery.

So that’s our guide to what Alternating Current means for EVs. If you found this useful please leave a comment below, and give this video a thumbs up so we know you liked it. And we’ll see you on the next one.

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