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Interconnecting Smoke Alarms, And Capacitive Coupling ?

Hello:

Have been going around the circle with this, and would sure apprciate any thoughts, or help.

Moved into a new house, and replaced some really old smoke detectors with 3 new Kidde AC wired-in ones. There is a three conductor (plus gnd wire) running between them.

When hooked up as individual units, all is fine.

When interconnected via the red wire in the cable, they all just keep going off.

To the best of my knowledge, there is absolutely nothing else on this line. When the smoke detectors are not hooked to it, it is truly floating, I believe.

But, with nothing on it, I measure about 2 to 4 volts AC, which is apparently enough to trigger them., when they are hooked to the line in interconnect mode.

Voltage seems high, but others have told me that it is possible via capacitive coupling. True ?

A kidde engr told me that when NOT triggered, the interconnect line has 0 volts on it. So, how can they ever work ?

Any thoughts on this, and hopefully suggestions on how to interconnect these units without them always going off would be most appreciated.

Thanks, Bob

Reply to
Robert11
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See if you can, at minimum, get a wiring diagram for multiple units. Look for a "termination device", as well as daisy chaining of that red wire.

Reply to
Robert Baer

Yeah- RTFB!- either you have a gross wiring error, different AC circuits, or something else on the interconnect line. The interconnection puts out 9VDC referenced to the incoming neutral line- steady in smoke detect and pulsed in CO mode- so if your neutrals don't match it will nusiance trip.

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Your

4VAC reading, measured with respect to neutral I assume, suggests that there is some other load on the line/neutral circuit, remove it.
Reply to
Fred Bloggs

Bob,

Some smoke detectors operate on two wire systems and some on four wire systems. The difference between the two is that one type needs to be powered to operate. Therefore, if you have a four wire system, two wires are to power your smokes. Now, smoke detectors as well as burg. detectors use wire color codes as in DC to low voltage systems which is different than house wiring color codes. So your red wire is power and your black is ground. That leaves the other two wires. I'm sure that instructions came with your smokes and that you wired your smokes correctly. So this is not the problem. What you don't know is that your smokes operate on resistance which controls the amount of current passing through them. The old smokes operated on a different resistance than your new ones and when you hooked them up and powered them they all did their stuff. What you have to do is determine the current difference between the two smokes. If the specifications are not written on the old smokes than you have to place one of them into the circuit and using a multimeter measure the current through the device. If you don't have a current reading on your meter you can place a 1 ohm resister in series with the smoke and measure the voltage across it. The voltage will equil the current. Make sure that you pick a resistor that is rated for the wattage of the circuit. Then all you have to do is determine the current difference between the two smokes.If he new smokes pass less current than you have to add some value of resistance in series with the smokes and if they pass more current than you have to place some resistance in parallel with the smokes. You see the circuit has to see some constant resistance in order for it to determine that all is right. When smoke enters the detector the resistance changes within the decector and more current is allowed to pass causing the alarm to sound. The resistors you choose have to be determined by the series, parallel resistance equations. I really hope that I have explained clearly enough for you to understand. Please excuse my spelling.

Paul

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