Update to "what is the output voltage on a smoke detector?"

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brycenesbitt

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gadfly56

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Professional Engineer, Fire & Life Safety
In closed post http://forums.mikeholt.com/showthread.php?t=142644
there was much speculation about the output or interconnect voltage on a smoke detector.

Here's a "SPICE" model of a BRK interconnect:

View attachment 10798

Basically it is 9V, has 24K of input impedance, and will run a load of up to 300 ohms.
Full details are at http://www.edcheung.com/automa/smoke_det.htm

BRK does not want this used for a fire alarm interconnect.

They show great wisdom. The problem is that the relays are not supervised for failure. If you shut off the circuit the fire alarms are on, the "real" FACP won't have a clue.
 

brycenesbitt

Senior Member
Location
United States
They show great wisdom. The problem is that the relays are not supervised for failure. If you shut off the circuit the fire alarms are on, the "real" FACP won't have a clue.

Exactly. The official BRK RM4 is useless if the power's off.
The circuit in the linked example would work though: it's an opto isolator which runs off the battery power of the BRK alarm.
 
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