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What is a Reed Relay?

What is a Reed Relay?

“What is a reed relay? A reed relay is a small electromagnetic switching device that integrates a coil around one or more reed switches. The energized coil creates the magnetic field used to control the switching operation.”

 

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?
What’s Unique About a Reed Relay?
Electrical & Mechanical Benefits
What are Some Common Reed Relays Uses?
Conclusion
Additional Resources

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.

What is a Reed Relay?

A reed relay showing the electromagnetic coil energized with a resulting magnetic field.

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.

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.

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.

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.

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.

 

How a reed relay works

A basic reed relay application with a 5 Amp pulse applied to the coil.

What’s Unique About a Reed Relay?

What is a reed relay? Well, that answer goes beyond its physical nature and how it works. Reed relays perform uniquely in several ways. Especially when compared to other relay technologies. One major way has to do its Reed Technology principle. Reed switch relays are hermetically sealed from the outside environment. Therefore, no outside dirt, dust, and grime means a long life of wear-free switching. So, the reed relay can switch low level signals for billions of operations (load dependent). In contrast, electromechanical relays are subject to mechanical failure from outside impurities. Thus, can at best switch in the low millions of operations.

Most notably, 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 & Mechanical Benefits

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

  • Form A, B, C, and E types
  • Hermetically isolated switches
  • Reliable for intrinsic safety
  • Long life, 10^9 operations (load dependent)
  • Multi-pole, up to 8 switches per relay
  • Stable low contact resistance <150 mΩ  
  • High insulation resistance >10^14 Ω
  • Switching up to 10,000 VDC
  • Breakdown voltage/dielectric strength up to 15,000 VDC
  • Carry currents up to 5 A continuous (10 A pulsed)
  • Operate times 500 µs to 3 ms
  • Very low signal switching in nanovolts range
  • Shock resistant to 100 G, vibrations 50-2 kHz at 20 G
  • Wide range of coil resistances
  • Tested in accordance with AEC-Q200 (KT series)
  • Comply with UL, CSA, VDE, ATEX, IECEx etc. (select series)
  • Large selection of package styles and pin-outs

What are Some Common Reed Relay Uses?

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

ATE/Test & Measurement – insulation testers, DMM and oscilloscopes, semiconductor testers, multiplexers and switch matrices

  • Perfect isolation from control to load circuit and across the switch contacts
  • Can switch both low and high loads
  • High density
  • Long life
  • Low thermal voltage

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, reed relays work on a Reed Technology principle using magnetic fields to control the switching process. These components pack high performance in a small yet versatile package. Meeting the low-level switching and other performance needs not met by other relays. So, when meticulously designed to meet specific uses, the reed relay lives up to the high demands of emerging electronics!

Standex Electronics designs custom-made reed relays in many package styles that offer unique features. Contact our relay experts to get started on a design that meets your specific needs. 

Additional Resources

Take a look at our reed relay product line brochure for more information on the range of relays offered by Standex Electronics.

Reed Relays & Optocouplers product line brochure

Product Line Brochure – Reed Relays & Optocouplers

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