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How do Electric Cars go in reverse?

I was talking to a friend the other day, he’s not very technical. He looked at me and asked if your car doesn’t have a transmission, how does it go in reverse?

I didn’t see that coming, so after I explained it to him, I thought perhaps other people were curious as well.

First off, a regular gasoline engine only spins in one direction. The pistons rotate the camshaft which goes out of the engine towards a transmission. The transmission then turns that spin into forward propulsion or backward propulsion using gears. Seems simple enough.

So if most EV’s have no transmission how do they go in reverse? Quite simply, the motors spin backward. An electric motor has the ability to spin in both directions.

Even odder though is that technically, an electric car could drive just as fast backwards as it does forwards! Luckily manufacturers put a limit on that because you know someone would try it. Don’t judge me 🙂

Let’s get a little more technical. Electric cars use what is called a 3 Phase motor, which essentially means that it requires 3 wires to operate. Your home for example is typically a single phase. Two 120V power lines ( to give you 240V to run your dryer, stove, and such  ) and a neutral. On a 3 phase motor though there are 3 electrical conductors.

It makes the motors not only more efficient but more powerful as well.

Here is the cool part though, by simply switching two of the three wires around it will reverse the phase and the motor will spin backwards instead of forwards.

The great thing is not having to use a transmission for either forward or reverse gears is that it greatly simplifies the manufacturing of electric vehicles and it’s also one less thing to break as well. There is a reason that towns are littered with transmission shops. There are a lot of moving parts in a transmission and they are prone to failure.

Automatic transmission. Look at all those parts!!!

That doesn’t mean it’s the only way though. In the interest of thoroughness, There are some home builds that mate an electric motor to an already installed transmission. In this setup, the driver would select the reverse gear to back up. The motor acts exactly like the gasoline engine does, spinning in one direction only. I know that wasn’t the question you were asking, but I wanted to put it out there anyway. Like life, there is usually more than one answer to a question.

Oh, and one last thing, while doing a little research on the topic. It seems a Nissan Leaf holds the speed record for driving in reverse at an average of 55 MPH.  I told you someone would try it! Here’s a link to the article.