Slip ring (rotary electrical joint)

01

Define the circuits, ratings and data

Moog describes a slip ring — also called a rotary electrical joint, collector or electric swivel — as an electromechanical device that transmits power and electrical signals from a stationary to a rotating structure, built from a ring assembly that gives one or more circuit paths over 360°, brushes in a brush block that contact the rings, input and output leads, and optional connectors. To specify a high-performance slip ring it lists the data bus (for example Profibus, Ethernet or FireWire), cable type, maximum cable length, maximum data rate and error rate, maximum diameter and length, number of circuits and their voltage and current ratings, maximum rotational speed and the operating environment. [1]

Senring's M-series capsule slip rings come in outside diameters of 6.5, 7.9, 12.5, 15.5, 22, 25 and 30 mm, with 4 to 56 circuits and current options of 0–5, 10, 15, 30 or 50 A, for control, video, HD and Ethernet signals in speed-dome cameras, stage lights and drones; its range also lists through-hole, pancake, PCB, high-current, high-speed, high-temperature and waterproof slip rings, Gigabit Ethernet, USB and HD-SDI slip rings, fibre-optic rotary joints and rotary unions. [2] [3]

Editorial calculation: a 3 kW, 400 V three-phase load draws about 3,000 ÷ (√3 × 400) ≈ 4.3 A per phase, so each power ring needs a rating above that with margin for start-up current and temperature; add separate rings for protective earth and for signals. [1]

Give the supplier the number of power circuits with current and voltage on each, signal and data circuits with bus type and data rate, any fibre-optic or fluid passages, maximum speed and duty, torque limit, outside diameter, length and through-bore, mounting, ingress protection and temperature range, required life and quantity.

02

Choose the contact type, speed, torque and size

Mercotac describes brush-type slip rings as a rotating ring rubbing against a graphite or metal brush, and lists wear, high resistance, oxidation and resistance fluctuations causing electrical noise as problems of that interface, offering brushless slip rings as the alternative. [4] For its brushless units it defines the voltage rating as the maximum AC or DC voltage before the insulation is overcome between circuits, the current rating as the maximum current before overheating, warns against undersized wires, poor connections and soldering to the tabs, and notes that single-conductor models have no voltage rating and an uninsulated body. [5]

Its rotational note says the units work from 0 rpm up to the model's maximum, in either direction, preferably with the body rotating to minimise bearing load, with mounting eccentricity below 0.005 in TIR; larger models have lower maximum speeds, faster rotation generates more heat that adds to ambient and current-induced rise, exceeding maximum rpm can open contacts, and break-away torque exceeds running torque. [6]

Editorial note: the temperature limit ties current, speed and ambient together, so give the supplier all three for the worst case rather than each at its own maximum. [6] [5]

03

Compare what suppliers offer

The companies in the manufacturer list below show this product on their own websites. Confirm the legal seller, factory and scope for your order.

Ask each supplier for the drawing and data sheet with circuits, current and voltage per circuit, contact material, insulation and dielectric tests, data performance for the bus you use, speed, torque, IP rating and expected life. [1] [2]

04

Trace what each part controls

This is a functional reference built from the sources cited; it is not one maker's specification.

05

Fill the specification fields with values for your joint

A slip ring quotation needs values for your rotating joint. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the circuit, motion and envelope data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Power circuits: [count; A; V]
Signals/data: [count; bus; Mbit/s]
Other passages: [fibre; air; fluid]
Motion: [rpm; continuous; reversing]
Torque limit: [N·m]
Envelope: [OD; bore; length]
Environment: [IP; °C]
Life/quantity: [revolutions; units]

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