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Cheap way to detect power failure? Codger needs ideas


Active Member
Warning - rambling post before I get to the point at the end, but thats par for the course...

So the power went out here yesterday when a giant oak with shallow roots, too much rain, and a gust of wind all came together. No one was injured and it trapped us all in our little neighborhood for the day, forcing everyone to actually talk to each other (in large part about when the power would come back, and also for me to say, Yes, I do have generator gas, yes, it is still good because theres this stuff called Stabil you should try, and yes, you may have some. But thats another story about how todays men dont know how to prepare for squat, and it makes me sound old and even more codgery, and if you're reading this on CTech theres a decent chance youre not in that camp as youre also a somewhat competent human. But anyway...

This whole episode got me to thinking about a cheap way to build a simple power outage detector that would connect to a zone on a security system (Elk M1G in my case), thereby notifying as to when the power goes out and comes back on. And, before someone tries to remind me that the Elk will tell me that automatically with a simple text, please understand that my Elk and internet and ISY are powered by a dedicated circuit that is in turn powered by a repurposed server UPS that is in turn connected to four 110AH batteries wired in series to 48V to power that UPS. So, it basically doesnt lose power for quite some time (better part of a day or more). Thus... I need a device to tell me weve lost power when Im away from home other than the neighborhood soccer moms and their soccer hubbies on FB, as I generally try to ignore those posts (and FB in general, come to think of it). I know I could go spend $70 or more, and maybe pay another subscription fee, to solve this. But that goes against my codgery nature and seems silly when I likely have a bunch of parts laying around that should accomplish the same thing. Maybe a RIB, mounted in a box? Anyone already solved this one and care to share?


Active Member
Other than what USM posted, check the back of your UPS. Some of the rackmount data center units will have terminals on the back that go to a relay to provide a switch closure on power fail.

Love the story BTW, I’m almost 51 and the state of the 20 and 30 something males in my neighborhood make me cringe.


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Senior Member
Our hydro utility has a web service that will notify you when the power is off at your house. Usually an estomate of how long before it will be repaired is uncluded and regular updates are sent once they understand the problem or it power is returned.
With the smart meters these days, utilities know the voltage at every metered service entrance.


Senior Member
How about a 120VAC relay with the coil wired to a cord plugged into a standard outlet and the NO contacts wired to the zone.
Power fails, the contacts open.
Power restored, the contacts close.
There are RIBs that properly isolate the high and low volatage sides.

Or use a 12V relay and use a 12VDC wall wart plugged into that same outlet across the coil.


Active Member
I do exactly this at my place with a relay.  240VAC coil relay (so 110V for you guys) and the contacts are fed back into the panel.
If you have multiple phases then just use a single relay per phase if you think you will drop only one phase (unlikely)
You can look at the UPS as it will have contacts as indicated, but what I would suggest is that you use that as a warning indicator for UPS health - how do you know it is in operational condition?  Most commercial/home UPS are a off line battery that is cut in when power fails so if your batteries are stuffed then you have no (or very little) power/run time.  The UPS will do health checks on itself to warn of this.


Active Member
UpStateMike - Perfect. Thanks! On order.

All - Thanks for the ideas. Completely forgot about the UPS, which would likely work as well, although it would be plugged into a circuit powered by the gennie so I still need this device to tell me when power is back on from utility (will connect to off-gennie circuit).

Will keep everyone posted once I install it.