Brief description

A relay is an electrically operated switch. It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.

Use / Function

• Isolation: Controlling a high-power circuit with a low-power signal (protecting the operator or delicate electronics).
• Logic: Building early logic circuits and computers before transistors.
• Signal Amplification: Using a weak electrical signal to switch a stronger one.
• Remote Control: Operating switches from a distance via telegraph or other wires.
• Scale: Household appliances to industrial automation and telephone exchanges.

Operating principle

• Electromagnetism: An electric current through a coil creates a magnetic field.
• Mechanical Action: The magnetic field attracts a movable iron armature.
• Switching: The movement of the armature physically opens or closes electrical contacts.
• Spring Return: When the current is removed, a spring pulls the armature back to its original position.

How to create it

1. Electromagnet: Wind a coil of insulated Copper Wire around an Iron core.
2. Armature: Mount a movable iron piece (armature) on a pivot or spring near the electromagnet.
3. Contacts: Attach electrical contacts (ideally made of Silver or copper) to the armature and the fixed frame.
4. Assembly: Arrange it so that when the coil is energized, the armature moves to touch (or separate) the contacts.
5. Technical Level: Intermediate. Requires precise alignment and reliable mechanical movement.

Materials needed

• Essential: Insulated Wire, Iron core and armature, conductive contacts (Silver or Copper), spring.
• Support: Plastic or Wood base for mounting.
• Tools: Wire cutters, pliers, soldering iron.

Variants and improvements

• Electromechanical Relay: The standard type described above.
• Solid State Relay (SSR): Uses semiconductors (like Transistors) to switch current without moving parts.
• Reed Relay: A small switch operated by an external magnetic field, enclosed in a glass tube.
• Latching Relay: Stays in its last position even after the control power is removed.

Limits and risks

• Mechanical Wear: Contacts can wear out or corrode over time due to sparking (arcing).
• Speed: Much slower than electronic switches like transistors.
• Noise: Produces an audible “click” and can generate electromagnetic interference.
• Arcing: High-power switching can create a plasma arc between contacts, potentially welding them shut.