Slip Rings in DC Motor

Paul Hadley
09/26/201926th September, 2019
Filed under Car Topics

Slip rings are very common to find in a DC motor but most people (even some young engineers) mistaken the slip ring in an AC motor for a split ring which is used in DC motor.

It’s very simple to mix up these two, but once you learn the difference – we promise you, you’ll never mistake them again.

But mistaking these two can be a problem. They might look similar, but they have a different purpose – and if you make a wrong call at the wrong time, it could cost you a lot of money.

In this article, you’ll find everything you need to know about slip rings and their function in DC motor. Therefore, sit back, relax, and enjoy the gem of knowledge you’ll discover in this post.

Here are some of the most helpful things you are going to discover in this post:

  • What is a Slip Ring?
  • The Main Function of a Slip Ring in a DC Motor
  • How Does Slip Ring Work?
  • The Difference Between Slip Ring in an AC and DC Motor
  • Conclusion

What is a Slip Ring?

In case you’re totally new to slip rings and their benefits – let’s begin from the start.

A slip ring is a device that connects stationary and rotary part of a device (most of the time electrical) while it allows transmission of power and signals (electrical).

Therefore, slip rings provide one of the key features that are necessary for almost any industry out there. Hence, this is the reason you can see slip rings in almost any electromechanical device no matter its industry.

As we’ve mentioned earlier, slip ring is used in both DC and AC motors, and the chances are you’ll be able to find a slip ring in one of these devices is about 99%.

But what does a slip ring do in DC motor? Let’s jump straight into it!

The Main Function of a Slip Ring in a DC Motor?

Even though the slip ring is a device that is pretty versatile, it actually does two different things in both DC and AC motor.

Therefore, the main function of a slip ring in a DC motor is to reverse the polarity of a current which is located in the armature windings of a DC motor.

Another thing you should remember is that due to this role of a slip ring in a DC motor, slip rings in DC motor are also known as commutators because of their design. They aren’t designed as a full circle (ring) yet have a small gap to improve their role in a DC motor.

However, you shouldn’t mistake slip rings in a DC motor with split rings. These two are totally different devices that have a different purpose. In some cases, you might find split rings replacing slip rings.

Even though these two sound very similar – keep in mind they’re not and you should avoid mistaking them as that is a rookie mistake you don’t want to make when working on a project.

But why do slip rings reverse the polarity of a current in a DC motor?

It’s quite simple to understand. Number one reason is to keep the torque of the DC motor from reversing while it’s working. Slip rings do this by reversing the current at the point when the coil moves at about 90-degree angle to the magnetic field.

Once the slip ring reverses the current, torque of the DC motor stops (or reduces) for a second, and exactly this action stops the torque from reversing. And as we all know, reversing torque would be really bad for a DC motor.

How Does a Slip Ring Work?

We’ve just explained how a slip ring works in a DC motor, but this is an exception which only applies to the DC motor.

The most standard slip rings work on a bit different principle – which then slightly changes depending on the industry or a device it’s being used in.

If you’ve ever seen slip ring in person, you’d notice that slip ring actually looks like a ring. It’s a ring-shaped device that consists of a stationary part (which is often a metal brush).

This brush rubs alongside of a rotating ring. This way, the current is being conducted and the connection is made at the same time – allowing slip rings to make a contact and transfer current from a stationary to a rotary part of the device.

The Difference Between Slip Ring in an AC and DC Motor

As we’ve mentioned earlier, there is a big difference in a standard slip ring and a slip ring which is being used in a DC motor.

Also, there’s a slip ring which is being used in an AC motor – which also varies from both standard type and a slip ring that can be found inside a DC motor.

The main difference between these two is the purpose. As you know by now, slip ring in a DC motor reverses the polarity of the current.

However, what slip ring in an AC motor does is it adds the resistance to the windings in order to keep the speed and current of both rotor and stator the same.

As you can see, even though slip rings work differently, they’re still producing the same results which are the ability to transfer signal and power from stationary to the rotary device.


Slip rings might be confusing at first, but once you understand their role, purpose, and the way they’re built – the confusion is eliminated.

Whether you’re a student or an engineer, you’d want to know the difference between a few of the most common slip rings.

This will help you to know how to properly apply slip rings in almost any of the electrical devices out there. But you will also know how to recognize one and this might tell you a lot about the way a device works.

Hopefully, by the end of this post, you might feel like an expert on slip rings in DC motor – and that’s just the beginning!

Feel free to leave a comment down below if you have any questions or would like to share something interesting!

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author avatar Written by Paul Hadley

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