Understanding Reed Switches & Reed Relays

This video describes what reed switches and reed relays actually are. It details how they work and how they are used as well as giving some circuit design hints and tips.

The reed switch is the basic element and this consists of two ferromagnetic reeds or contacts held within a glass envelope. The reeds overlap so that when they close they make contact.

When a magnetic field is applied, the reeds become magnetically orientated to the field, making the two ends of the reeds opposite poles.

When the external field becomes sufficiently strong, the attractional force will draw to each other, closing the contact and making the circuit - the basic reed switch. Essentially it is a magnetic switch.

These reed switches are used for many applications including sensors, i.e. magnetic reed switch sensors, etc.

Reed switches also form the main element of a reed relay and they are used in electronics as fast acting mechanical switches.

The bar magnet we saw earlier can be replaced by a coil. When a current passes through the coil a magnetic field is created and this acts to switch the reed relay over.

Reed relays come in a variety of sizes and formats. They can be dual in line, single in line for PCBs of they can be much bigger for larger current applications. There are several manufacturers of reed relays so there is a good choice.

Reed relays are used in circuits for many reasons: they are fast acting, they are reliable, they have a low ON resistance and high OFF resistance and they also provide isolation between the actuator and switched sides of the circuit.

[BigMike]

I have Reed switches all around my house at this point (cabinet & closet lighting, intruder alerts on windows, etc), and I've tried just about everything I can think of (or Google), but I have yet to find a way to get the contacts inside the reed switches to stop fusing together after a couple of weeks to a couple of months! Even using as little as 5v 60mA, they always seem to go bad pretty quickly.
Any ideas would be appreciated....

[ricksampson]

Can you please discuss the various methods of recovering the BEMF generated when a relay coil is de-energised.
Recovery values of 80-90% of the input power in a pulsed relay driver circuit are possible, given the correct circuit/coil parameters.
Cheers.

[Ezzell_]

Does the orientation of the reeds and or the the magnetic field come into play?

[flixi]

thank you for the video, its very helpful