A slip ring allows for the transfer of current or signals between a static source and a rotating object without wires. It uses a conductive ring and brush to maintain contact. Slip rings are used in generators, motors, and other applications where low resistance connections are needed. Mercury can be used for low resistance connections, but it is toxic. Slip rings can transfer data and signals as well as current.
A slip ring is a device that allows for the transfer of electric current or a signal between a static source and a rotating object without the use of a physical wired connection between the two. A slip ring arrangement makes this connection with a conductive ring attached around the rotating component and a spring brush or contact on the stationary component. This brush rests on the rotating ring and maintains constant electrical contact with it while remaining static. Rotating ring devices have various applications.
Passing a current or signal between rotating and stationary objects poses an engineering puzzle that is best solved by using a sliding, low-friction contact between the two. In applications involving a rotor such as those found in generators and motors, the best way to achieve this is to use a solid slip ring. It consists of a conductive ring, typically made of high quality polished copper, that runs around the rotor shaft. This ring is isolated from the shaft and wired to the rotor windings. A spring-loaded brush carrying electric current is positioned to maintain constant pressure on the ring throughout its rotational stroke thus completing the circuit.
Brushes are usually made of a conductive material such as carbon which is softer than the ring. This material is used to ensure that the brush, rather than the ring, wears out first as the brush is easier and cheaper to replace when it wears out. In applications requiring a low resistance connection, mercury can be used to replace carbon brushes. Due to its toxicity, however, it cannot be used in pharmaceutical or food industries where mercury contamination poses a health risk.
The use of a slip ring system is not limited to the passage of electric current. This transfer is also not limited to a static to rotor switch; current, signal or data can be transferred from the rotating component to the static element. As long as the brush and ring surfaces are kept clean and free from corrosion and nicks, the slip ring connection can be kept very “clean” with a minimum of sparking, data interference, and audio noise. Slip ring applications include rotating beacons or beacons, alternators, generators, and slip ring electric motors, and make use of a variety of slip ring and contact designs and materials.
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