Capsule slip rings

What a capsule slip ring is

A capsule slip ring is a compact, solid-centre rotary electrical joint that passes power and signals from a fixed frame to a rotating assembly. Precious-metal brushes, usually gold on gold, ride on a stack of small-diameter rings inside a sealed cylindrical housing, so surface speed, contact noise and wear all stay low. Because there is no bore, the unit sits on the axis of rotation, typically fixed by a flange at one end with flying leads leaving each side. Capsules carry many signal circuits and modest power in a very small envelope.

When to choose a capsule slip ring

Choose a capsule when the centre of the rotating axis is free and space is tight, as in camera heads, small turntables, sensor heads and robot wrists. Small rings give low drag torque, low electrical noise and long life, which suits analogue, encoder and low-level data signals. The trade-offs are current and access: power rings are typically limited to a few amps each, and nothing can pass through the middle. If a shaft, hose or cable must run along the axis, a through-bore design is the better fit.

How to specify capsule slip rings

• Number of circuits, split into power, signal and data
• Current per circuit (A) and working voltage (V AC or DC)
• Maximum and continuous speed (rpm)
• Envelope: outer diameter and length (mm)
• Signal types: analogue, encoder, RS485, CAN, Ethernet or video
• Ingress protection (IP code) and temperature range (°C)
• Lead length, wire gauge and connector terminations

Common mistakes

• Pushing one ring past its current rating instead of paralleling two or more rings per conductor
• Mixing motor power and low-level signals on adjacent rings without screening or allocation planning
• Fixing the rotor rigidly to a shaft that runs out, so bearing loads go through the capsule
• Letting the leads act as the anti-rotation device instead of fitting a proper torque strap or pin

Series compared

Maximum figures across each series, summarised from manufacturers' published data on the date shown on each series page. Always confirm against the current datasheet.

Where capsule slip rings are used

Capsule slip rings: frequently asked questions

What is the difference between a capsule and a through-bore slip ring?

A capsule slip ring has no central hole and mounts on the end of the rotating axis, which keeps the rings small, drag torque low and life long. A through-bore slip ring has a hollow centre so a shaft, air line or cable can pass along the axis. At equal rpm, through-bore rings run at a higher surface speed and are larger, so choose by whether the axis is free.

How much current can a capsule slip ring carry?

Signal rings in a capsule typically carry well under an amp, while dedicated power rings are commonly rated at a few amps up to around 10 A depending on the design. For a heavier load, several rings are paralleled on one conductor, which uses up circuit count and length. If the machine needs tens of amps, a through-bore or purpose-built high-current unit is usually more practical.