With regard to the First Alert interconnected smoke alarms, and maybe all of the similar type, what is the voltage on the yellow wire that is used for the interconnect signal to cause all detectors to sound when one detects smoke?
9VDC from what I’ve read, with the pattern being continuous/steady for smoke & pulsed for CO.
Yep, and it’s the same thing for Kidde alarms. I’m not sure if the CO is exactly the same on First Alert, but I know Kidde alarms use a 9v T4 pattern on the interconnect wire to signal a CO alarm.
Next question, if there is an AC power failure, does this interconnect voltage come from the 9 volt battery? First Alert sells a relay that connects to the yellow wire and will close to indicate an alarm. However they say that this is not approved to connect to a central fire alarm system and they further say that it does not operate durning a power failure. Now is this an AC power failure or a battery failure?
“The hardwired interconnect system in our alarms uses the traveler wire in standard 12/3 or 14/3 home wiring to link AC-powered units. Communication between alarms occurs via a DC signal on the orange wire, known as the Interconnect wire:
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When a Smoke or Heat detector is triggered, it sends a constant 9V DC signal across the interconnect wire, prompting all interconnected Smoke and Heat alarms to activate.
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When a CO detector is triggered, it sends a pulsing 9V DC signal, which activates all interconnected CO alarms. “ (from email with first alert)
AC most likely, to save as much battery as possible
Simplexwomen - you have stated two directly contradictory things in the above two posts. In the first you say that the signal is DC and in the second you say that the signal is most likely AC. You quote an email from the company that says DC, but the company website says the signal will not trigger a relay attached to the signal wire if the 120 vols AC power fails. Has anyone ever taken a meter and checked it? Clearly the manufacturer’s information as posted on its website is inaccurate.
I found the instruction for the relay and these say additional contradictory things. I guess the take away from this is that First Alert instructions and spec sheets can not really be trusted to be accurate. I am really suspicious about the relay functioning in the event of a power failure because the relay module is connected to the 120 volt AC line in addition to the interconnect line. Powering the relay from the small 9 volt battery does seem to be asking for trouble. The mystery continues!
In my experiences, the smoke alarms will always send out a 9v signal for interconnect, but they will only get it from the battery during a power failure. On AC power, they get the signal from the alarm’s internal power supply. Also, I’ve never seen a smoke alarm relay that can work during a power failure.
According to NewAgeServerAlarm in this topic, a wired smoke detector’s interconnect cannot function without 120VAC power, meaning that if the power has failed only one detector on an interconnected system of them will sound (as also said by NewAge Gentex’s supposedly can, but that’s apparently never been verified to be true).
This is correct to the best of my understanding and knowledge (all the smoke alarms I’ve tested so far have put out valid interconnect signals when fed power via the battery connections)
Power is rectified to dc coming into the alarm, I was talking about the interconnection
OK, got it. This is all making sense to me now. The relay is TRIGGERED by the interconnect signal but the power to close the relay comes from the AC power line, which means that the relay will not operate during an AC power failure. But, all smoke alarms that are on the interconnect circuit will sound even during a power failure. Another issue - if I use this relay to connect to the monitored house alarm, and I push the test button without notifying the alarm company ahead of time, the fire department will show up and I think they will be in a bad mood.