Dr. Frankenstein’s Latching Relay

September 22, 2020
Tech Tuesday

A couple of months ago, someone called our Technical Support hotline to see if we have a latching relay for their application. Their application was to turn some lights on and off in a medical facility. They had a momentary switch with no voltage (dry switch), and they needed the switch to provide a latched 24Vac signal to control a separate device. Basically, the first press and release of the switch would activate the 24Vac, and the second press and release of the switch would deactivate the 24Vac. The momentary switch was a Form C contact (Single-pole, Double-throw).

After scouring our website for the right product solution, nothing came up to work. The customer was in a situation where they would need some kind of solution and cost was not too much of a concern. I began rubbing my hands together in a maniacal fashion as I thought of all the ways to latch a 24Vac output. After half the day testing and wiring, here was the cost-effective solution I landed on for this customer in the application they were facing:

Here are the products that were used in this setup:

  • RIBMN24C-4T
  • RIBMN24C – you need quantity five (5) of the RIBMN24C relays to make this bad boy work
  • A 24Vac transformer for input power to the circuit

As indicated in the diagram above, the SPDT switch on the right-hand side of the wiring diagram will short the pink line to 24Vac Common (the little triangle symbol), which latches/un-latches the 24Vac output on the purple line. Explaining the circuit can get long-winded here, so feel free to reach out to us for an in-depth explanation. The bottom line was it worked! Cue mad scientist-like laugh

It was great to do some problem solving with that customer, so feel free to reach out to us for help with anything RIB relay-related. The crazier the better!


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About the Author

Meet Samuel Klennert – you can call him Sam. He was born and raised amongst the farmland of Indiana, which included corn, soybeans, and sometimes wheat. Sam graduated from Purdue University with a Bachelors degree in Electrical and Computer Engineering Technology in 2015. He has a focus in analog circuitry and power electronics, but he’ll give software a try from time to time – just not that digital witchcraft!

Outside of work, Sam enjoys outdoor activities including (but not limited to) hiking, mountain biking (or just really-big-hill biking), and camping. Call Sam for tech support today – he’ll give his best effort to any task at hand!