Slip ring

A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring can be used in any electromechanical system that requires rotation while transmitting power or signals. It can improve mechanical performance, simplify system operation and eliminate damage-prone wires dangling from movable joints.

Also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels, or electrical rotary joints, these rings are commonly found in slip ring motors, electrical generators for alternating current (AC) systems and alternators and in packaging machinery, cable reels, and wind turbines. They can be used on any rotating object to transfer power, control circuits, or analog or digital signals including data such as those found on aerodrome beacons, rotating tanks, power shovels, radio telescopes, telemetry systems, heliostats or ferris wheels.

A slip ring (in electrical engineering terms) is a method of making an electrical connection through a rotating assembly. Formally, it is an electric transmission device that allows energy flow between two electrical rotating parts, such as in a motor.

Typically, a slip ring consists of a stationary graphite or metal contact (brush) which rubs on the outside diameter of a rotating metal ring. As the metal ring turns, the electric current or signal is conducted through the stationary brush to the metal ring making the connection. Additional ring/brush assemblies are stacked along the rotating axis if more than one electrical circuit is needed. Either the brushes or the rings are stationary and the other component rotates. This simple design has been used for decades as a rudimentary method of passing current into a rotating device.

Some other names used for slip ring are collector ring, rotary electrical contact and electrical slip ring. Some people also use the term commutator; however, commutators are somewhat different and are specialized for use on DC motors and generators. While commutators are segmented, slip rings are continuous, and the terms are not interchangeable. Rotary transformers are often used instead of slip rings in high-speed or low-friction environments.

A slip ring can be used within a rotary union to function concurrently with the device, commonly referred to as a rotary joint. Slip rings do the same for electrical power and signal that rotary unions do for fluid media. They are often integrated into rotary unions to send power and data to and from rotating machinery in conjunction with the media that the rotary union provides.

The basic principle of slip rings can be traced back to the late 19th century when they were initially used in early electrical experiments and the development of electrical generators and motors. With the advent of the Industrial Revolution and the increasing demand for electrical power, the technology behind slip rings started to evolve. They became essential components in large-scale electrical machinery, such as turbines and generators, allowing for the transfer of power and signals in machines where a part of the machinery needed to rotate continuously.

Slip rings are made in various types and sizes; one device made for theatrical stage lighting, for example, had 100 conductors. The slip ring allows for unlimited rotations of the connected object, whereas a slack cable can only be twisted a few times before it will bind up and restrict rotation.