Slip Ring and its Use in the AC Motor

Slip Ring and its Use in the AC Motor

Slip rings are tiny devices that have a simple purpose and yet their versatility makes it usable in almost any industry in so many devices, equipment, and even heavy machinery.

AC motors are very efficient but they need resistance to reduce the voltage and limit the starting current to ensure an efficient and smooth start.

That’s where slip rings come into play and help AC motors so there are high chances you’ll come across slip rings in AC motors.

And in this article, you’ll learn more about slip rings, how they help AC motors, and what benefits you can expect in the long run – so keep on reading!

What is a Slip Ring and What is its Purpose?

slip ring

A slip ring is a device that was made to solve one simple but important problem which is the wire winding problem in devices that have a rotary part to it.

Therefore, slip rings were introduced to bridge the gap between the stationary and rotary parts of a device. This helped eliminate the wire winding problem, but also remove and reduce the wires hanging around the joints which is extremely hazardous for any type of equipment and could lead to a serious downtime of a machine.

However, slip rings are also very well known for their versatility. While providing such a solution, they can also transmit electrical signals, power, data, and much more from a stationary to a rotary part of a machine by providing secure contact.

Since slip rings are very durable, simple, and yet so versatile that they can fit so many different scenarios and provide a solution to a couple of different needs, there are 6 different types of them.

So you can expect to find slip rings in almost any device that has a rotary aspect to it, no matter the industry.


How Does a Slip Ring Fit in the AC Motor?

AC motor

While slip rings can help transmit electrical signals, power, data, or any other medium depending on the type of slip ring, they’re not used for this purpose in the AC motor.

This shouldn’t come as a surprise since slip rings are known for their versatility.

Instead, slip rings are used to add resistance to AC motors directly into the rotor windings. And there isn’t only one slip ring, but an AC motor with windings uses 3 slip rings.

These types of slip rings are made out of copper (or alloy) and are mounted to the motor shaft, yet have no connection with the motor.

Each slip ring connects to one motor phase where they maintain constant contact while the motor rotates, providing a constant resistance to the motor windings

This allows the motor to produce high torque with a low current. But the interesting thing is that slip rings only help until the motor reaches its operational speed. That’s when slip rings are shorted out and drop contact so the motor then runs as a standard AC motor.


Benefits of Slip Rings

The most known benefit of a slip ring is the ability to eliminate a wire winding problem which works by eliminating wires hanging around the joints of a rotary machine, and yet by providing a superb contact between stationary and a rotary part of a machine.

However, due to the versatility of slip rings, they are also good at adding resistance to the AC motors, limiting the speed of blades on wind turbines. They are even good at providing a slow and smooth operational start to machines that require precision such as excavators or other heavy machinery.

Slip rings are also known for being able to withstand high load capacity and still provide a slow and precise start.

With so many different types, they can also transmit other mediums other than signal, power, and data. Other types of slip rings can transfer fluid, water, coolant, gas and oil, ethernet, fiber optic, and more.

Therefore, overall, slip rings can boost mechanical performance, simplify systems, and eliminate wires in places where they can be hazardous.

On top of that, with modern slip rings, power transmission can even be wireless and they can last much longer than the standard slip rings.


Types of Slip Rings

slip ring

There are 6 main slip ring types and they’re the following:

  • Pancake ring
  • Mercury contact ring
  • Ethernet ring
  • Miniature slip ring
  • Fiber optic ring
  • Through hole slip ring

However, there are many more variations and sub-types of each slip ring type. On top of that, there are custom slip ring solutions for certain industries, devices, equipment, or innovations you should also consider.

Companies such as Moflon have been producing slip rings for the past 30+ years for industries such as food and beverage, aerospace, aviation, marine dredging, factory automation, radars, robotics, wind turbines, monitoring, and medical imaging equipment, and more.

Moflon even produces custom slip ring solutions for companies and innovators who could use the purpose of a slip ring and yet just need a custom-built slip ring to fit into their equipment.

On top of that, there are also advanced slip rings such as a wireless power slip ring that comes with an unlimited RPM or a brushless slip ring which drastically improves the lifespan of a slip ring.

Therefore, with so many different types, it’s really not a surprise to see slip rings being used even in the AC motors since they are very versatile and yet durable so they can easily withstand working conditions.


Not many people even know what slip rings are and how they are used in AC motors. However, slip rings are a very simple invention that’s very versatile and fits so many industries in so many ways.

Therefore, in this article, you can learn everything you need to know about slip rings, their functionality, but also its purpose in AC motors, and why AC motors wouldn’t work as efficiently without slip rings.

One thing is for sure, slip rings are almost everywhere where rotation is so it is most likely you’ll find it in almost any device, machine, or equipment that has a rotary aspect to it.


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