How does a slip ring work?
A slip ring
(in electrical engineering terms) is a method of making an electrical connection through a rotating assembly. Slip rings, also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels, or electrical rotary joints, are commonly found in electrical generators for AC systems and alternators and in packaging machinery, cable reels, and wind turbines. One of the two rings is connected to one end of the armature winding and other one to the other end of the armature winding.
A slip ring connector
is used to continuously transmit electrical power, signal or data from a stationary source to a rotating destination, or vice versa. They are available in a wide variety of configurations, termination types and materials to fit most applications.
A slip ring is an electrical connector designed to carry current or signals from a stationary wire into a rotating device.
Typically, it is comprised 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 electrical 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 wire is needed.
This simple design has been used for decades as a rudimentary method of passing current into a rotating device. Some other names used for slipring
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.
A slip ring consists of a conductive circle or band mounted on a shaft and insulated from it. Electrical connections from the rotating part of the system, such as the rotor of a generator, are made to the ring. Fixed contacts or brushes run in contact with the ring, transferring electrical power or signals to the exterior, static part of the system.
This system is similar to the brushes and comutator, found in many types of DC motors. While commutators are segmented, slip rings are continuous, and the terms are not to be used interchangeably. Slip rings can also be used where electrical power or signals need to be transferred to a rotating device, such as an aerodrome beacon, rotating tank, power shovel or radio telescope. Rotary transformers are often used instead of slip rings in high speed or low friction environments.
Slip rings are always part of a larger mechanism with a need to pass specific electrical power and signal wires through a rotating surface. The mechanism the slip ring is part of operates in an environment such as an aircraft or a ship. Therefore, to create a slip ring design that will succeed in its application three criteria must be satisfied:
- Physical dimensions, including attachment arrangement and de-rotating features
- Description of wires required, including maximum current and voltage
- Operating environment, including temperature, humidity, salt fog requirements, shock, vibration
More detailed slip ring requirements include:
- Maximum resistance between rotor and stator, usually expressed in milli-ohms
- Isolation between wires, expressed in dB
- Isolation from EMI sources outside the slip ring housing, also expressed in dB
- Starting and running torque, expressed in in-lbs
- Data wire descriptions
Common extra features that can be incorporated in a slip ring assembly include:
- Fluid rotary unions
- Coax rotary unions
- Fiber optic rotary joints
Electro-Miniatures can help you identify the specific criteria you need to establish to ensure your slip ring meets your design requirements.