What Is a Reed Relay? How It Works, Benefits, and Applications

If there are particular areas you need help with, feel free to skip to any of the following sections:

• Introduction
• What is a Reed Relay?
• How Do Reed Relays Work?
• Types of Reed Relays
• What’s Reed Relays Unique?
• Electrical and Mechanical Benefits
• Common Reed Relay Applications
• Conclusion

Introduction

In this blog we not only explain what a reed relay is but also some key performance features and common applications. The basis of the reed relay is Reed Technology which uses a magnetic field to control the switching operation. Simply put, a reed relay is a magnetic switching component integrated with an electromagnetic coil. Read on to learn more about what a reed relay is and what makes it so unique.

What is a Reed Relay?

A reed relay is a small electromagnetic switching device. Reed relays are made by placing a coil around one or more reed switches. Typically, the relay assembly is then over-molded, or epoxy sealed into a housing for added durability and handling. Connection pins and/or free wires exiting the relay allow for PCB surface mounting or thru-hole assembly.

How Do Reed Relays Work?

Now that you know what a reed relay is, let’s explore how reed relays work. First, it helps to know the types of reed relays to understand how they work. Form refers to the relays’ internal switch contact configuration. There are four contact forms, Form A, B, C, and E.

Types of Reed Relays

Form A (Normally Open)

First, is the Form A type which is the most common and rests in a normally open (N.O.) switch state. Form A relays remain OPEN or OFF until current passes through the coil. The electromagnetic coil produces a magnetic field equal to a permanent magnet. Finally, the resulting magnetic field closes the contacts, switching the relay ON. Conversely, when the coil current is removed, the switch turns off and the contacts return to their open state.

Form B (Normally Closed)

Next is our second type Form B relays which have normally closed (N.C.) biased contacts held by a magnet. So, the relay rests in the closed or off state until the coil is energized, opening the contacts. De-energizing the coil switches the relay back to its closed or off position.

Form C (Changeover / SPDT)

Third, is the Form C relay which is uniquely comprised of three contacts compared to the typical two. They are normally open, normally closed, and common. The common contact will swing from the closed contact to the open contact when switched on. When OFF the contact reverts to its resting closed state. Therefore, Form C types are also referred to as a double throw switch.

Form E (Latching / Bistable)

The fourth and final type Form E is what we call a latching or bistable relay. This relay can exist in either the N.O. or N.C. state with no coil power using a biasing magnet. The relays’ contacts maintain their last assumed position without activating the coil. To change the state of the contacts, the magnetic field must be reversed.

What’s Reed Relays Unique ?

Reed relays perform uniquely in several ways, especially when compared to other relay technologies.

Because the reed switch contacts are hermetically sealed, they are protected from dirt, dust, and moisture. This design enables exceptionally long life and wear-free switching.

As a result, reed relays can switch low-level signals for billions of operations, far exceeding the life expectancy of conventional electromechanical relays.

As a result, no other relay technology can switch zero voltage and current like the reed relays does! Moreover, semiconductor relays exhibit higher leakage current, and capacitance compared to reed technology. Therefore, offering many more unique advantages over other relay types. Read on to learn more about these performance features listed below.

Electrical and Mechanical Benefits

Reed Relays offer a wide range of unique switching advantages, including:

Key Electrical advantages include:

Mechanical benefits include:

Common Reed Relay Applications?

You will find reed relays used extensively throughout test and measurement, medical, alternative energy, and hybrid and electric mobility markets. That is because reed relays offer perfect isolation between the control and load circuits. Also meeting the requirements of reliability, accuracy, speed, and safety. Other common uses include high cycle count, high voltage, low voltage, low current, or RF switching.

Furthermore, reed relays can have multiple switches and switch forms in a single package. So, it’s easy to imagine all the ways that a reed relay can be used. Especially, given all the above-mentioned relay types and the convenience of compact multi-pole relay. For instance, below is a list of some common reed relay application examples.

Applications

Hybrid & Electric Vehicles

• Battery management, battery conditioning, power inverters
• High isolation from control to load circuit and across the relay contacts
• Carries very low current (detects current leaks)
• Meets creepage distances

Alternative Energy

• Solar inverters, power distribution
• Perfect isolation from control to load circuit
• High voltage switching
• Reliability
• Temperature shock resistant
• Long life

Medical

• Surgical generators, automated external defibrillators, isolation functions
• High isolation between control and load circuit
• Meets creepage and clearance distances
• High voltage switching
• Reliability
• Long life

Conclusion

In summary, a reed relay is a compact, high-performance electromagnetic switch that excels in low-level, high-reliability applications. Thanks to hermetically sealed contacts and exceptional electrical isolation, reed relays outperform many conventional relay technologies.

Standex Detect designs custom reed relays in a wide range of package styles and contact configurations. Contact our relay experts to develop a solution tailored to your specific application.