A pull chain switch is a simple mechanical device that uses a series of internal components to toggle the state of an electrical circuit each time the chain is pulled. It typically cycles power on and off with consecutive pulls.
At its core, a pull chain mechanism utilizes a ratchet-and-pawl system connected to a rotating element, often a wheel or cam. Pulling the chain engages this system, causing the wheel to turn a specific increment. This rotation manipulates electrical contacts, such as a copper strip, to either complete (turn on) or break (turn off) the circuit.
Based on the provided information:
- A tug on the chain activates the mechanism.
- This causes a wheel inside the switch to turn.
- The wheel turns in specific increments, for example, another 90 degrees with each pull.
- This rotation interacts with the copper strip (likely an electrical contact).
- After the wheel turns, the state of the switch changes, such as turning off after a tug.
The Cycling Action
The internal design dictates the sequence of states. A common setup for a simple light fixture switch is a two-state cycle:
- Pull 1: Turns the light On.
- Pull 2: Turns the light Off.
Some switches may offer multi-state operation, particularly in fan light kits, cycling through states like:
- Light On, Fan Low
- Light On, Fan Medium
- Light On, Fan High
- Light Off, Fan Off
Each tug of the chain advances the wheel to the next position in its cycle, changing the contact configuration accordingly. The mechanism is designed to hold the wheel in place until the next pull.
Key Components
While internal designs vary, common elements include:
- Pull Chain: The external interface.
- Ratchet: A toothed wheel.
- Pawl: A lever that engages the ratchet teeth to advance it and prevents backward movement.
- Rotating Wheel/Cam: Turned by the ratchet, it physically moves the electrical contacts.
- Electrical Contacts: Conductive pieces (like a copper strip) that are brought together or separated by the rotating element to make or break the circuit.
In essence, the mechanical energy from pulling the chain is converted into rotational movement that operates the electrical contacts, allowing you to switch a device on or off. The simple, reliable nature of this mechanism makes it a popular choice for overhead lights and fans.
