Discuss Mains powered smoke alarms in the Electrical Forum area at ElectriciansForums.net

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electric will

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Any one know if mains interlinked battery backed up smokes will set interconnecting alarms off during power failure, if they do then how, obviously no mains power to trigger, so still got the 9v battery, someone once told me they sent 9v down the interconnecting core, ok that's a positive to other smokes but what about negative? And that means having 230v ac and 9v dc in the same cable, suppose the cable is insulated to the higher voltage though.
 

Philpot

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Hi 230 v is supplied to each detector. That is reduced to 9v for operation of the detector. That means that the network of detectors are not reliant on the the 230v as long as the detectors have a 9v back up battery.
does that help

Phil
 
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electric will

electric will

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So the alarms use 9v all the time, so they must all have a 230 to 9 volt transformer in them, still can't see how the link dc pos and neg to each other, interlink cable 3c and earth, so live, neutral takes 2 cores, if the 3rd was 9v positive where's the neg for dc
 

telectrix

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might just share the neutral as 0V for both 230v a.c. and 9v d.c.
 
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electric will

electric will

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Tel, there's a thought I didn't think of that, still don't sound ideal though does it? Not sure I like the 230 and 9v in the same cable anyway.
 
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electric will

electric will

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A while ago I was going to connect a switch to the interconnecting cable in some alarms in a club, to put 230 to it, thinking they could use the switch for fire drills, good job I didnt, would have been interesting.
 

telectrix

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not a problem as each conductor is insulated to the highest voltage present. some security lights come with an audible sounder which you plug in anywhwere in the house. the sounder signal comes from the PIR through the mains wiring of the RFC.
 
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electric will

electric will

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I thought them sounders were radio linked, anyway I know how it'd work, like sending ethernet on ring finals
 
M

MarkieSparkie

A while ago I was going to connect a switch to the interconnecting cable in some alarms in a club, to put 230 to it, thinking they could use the switch for fire drills, good job I didnt, would have been interesting.
Your not alone in that idea. I know there will be an certain apprentice reading this thread later today who will be extremely red-faced with embarrassment and little funds, because he did exactly that and blew-up 50+ interlinked smoke detectors in a Sport Complex only a couple of weeks ago; instead of detecting smoke they were producing it!. :89:
 
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electric will

electric will

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Think next time I take one out I'll rip it apart to see how they work, I'm going with the combined neutral and negitive at the mo though
 
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MarkieSparkie

Think next time I take one out I'll rip it apart to see how they work, I'm going with the combined neutral and negitive at the mo though
The Neutral is common to both AC and DC supplies. Be careful how you dismantle a smoke alarm, as the ionising types contain a radioactive element, usually Americium. So don't break open the ionising chamber as the fine radioactive powder is easily inhaled or ingested.
 

tazz

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The interlink between most 230v /9v backup detectors use an optical isolator. this is basically and sealed led switch. The nuetral is used as part of link, basicall if one detector is activated a low voltage around 4-5v switches all others. The optical isolator is used to prevent 230v being introduce into the circuit. Hope this helps
 
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electric will

electric will

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Wouldn't have to be marked anyway, it's classed as a control wire like central heating, had this discussion with assessor a while ago. Then as the conversion went he didn't know if it'd be mains or low voltage either.
 

grantr37

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that type of opto-isolator won't stop mains voltage, it will pop....generally a 4N25 4 pin.....older style smoke detectors used a 5volt TTL AND to give an output high signal (condition) connected to the same track on the board as the test button.....connecting AC mains to the signal pin of the base on any unit by mistake will fry all the detectors on that chain, resulting in fault chirping and a burning PCB smell.....and the recycling facility (ionising type must be legally recycled and not binned due to radio-metals contained inside) new optical sensor alarms are non-radio emitting and can be binned/recycled as normal, these are phasing out the ionising scintillation detector hardware...
 
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