We had a power cut here for about 3 hours just after midnight (yes, I know I'm not the only one!) which set off a neighbour's burglar alarm. He wasn't able to turn it off and the thing went on and on for well over
2 hours until it ran out of juice. Question is, how does a well designed alarm deal with a power cut? How does it differentiate between that and somebody "tampering" with its innards? I'm off for a snooze now....:-)
On my oldish system there is a battery in the alarm control box which takes over when the mains power is cut thus maintaining the system so in effect it does not know that there has been a power cut. If this battery is dead or missing the wall box thinks that the alarm has been triggered as soon as the mains power goes off These batteries should last for at least 5 years but often get forgotten until a power cut occurs
The alarm box on the wall outside has in my case a capacitor which runs the noisy bit for however long until the box in the house is reset. the system then recharges the capacitor
Tony
Mine has a battery backup in the main control box. This should keep it going for quite a while in the event of a power failure. Once the battery is dead, I guess the bell box will trigger, thinking that someone has been tampering with the power supply. The bell box has a built in battery which will keep the alarm sounding for a while :-(
I think mine has a setting which allows you to alarm on power failure. Maybe your neighbour has this feature and its on (or maybe they just dont have a battery backup).
Alan
So, are the batteries in the bell box designed to last longer than the ones in the control box? If the system hasn't been maintained and the control box battery is dead, chances are the one in the bell box will be too. Anyone?
MBQ
What size capacitor is that? How long is "however long"?
MBQ
"Man at B&Q" wrote
**************************************************** So, are the batteries in the bell box designed to last longer than the ones in the control box? If the system hasn't been maintained and the control box battery is dead, chances are the one in the bell box will be too. Anyone? ***************************************************I just upgraded my alarm system including the bell box. The battery in the old bell box was still active - the system was 12 years old (from the stated install date). I had replaced the panel battery at 2 yearly intervals (since we took the place on 7 years ago) as a precaution.
Phil
In message , Stuart Noble wrote
The alarm would only go off if the backup battery in the control panel is dead, or dying. In my experience the battery will still show 12V+ terminal voltage but is unable to cope with the power drain when the mains goes off. I now replace my battery every 2/3 years.
Thanks Well, I imagine the battery in the bell box is working fine judging by last night's performance, so it sounds like the one in the control box is naff. What type of battery is it likely to be? Easy to find?
In message , Stuart Noble wrote
Yep, easy to find
Towards the smaller end of range of:
Its an intruder alarm battery from an alarm company Mine was from Abel Alarms over the counter about 8ukp Maplin sell them Ebay has them They are the same as many motor scooter batteries
Tony
What size capacitor is that? How long is "however long"?
MBQ
Difficult for me to tell as I suppose that I would have to undo the box on the wall to check the size and then switch off the mains power disconnect the battery in the control box and time the alarm whilst dodging objects being thrown by the neighbours and explaining to swmbo why am I doing this
Sorry can't help
Tony
That's right. I might be Stuart's neighbour, cos we had exactly the same problem over Easter - control panel back-up cell was utterly knackered, but sadly the alarm box back-up was able to keep going for hours. New 12v sealed cell on order now.
IIRC it's illegal under noise abatement legislation for intruder alarms not to have a 20 minute max cut-off time on the audible sounder.
Environmental Health would probably be the enforcement authority but are unlikely to do much unless it keeps happening.
Owain
OK, when I said battery, I actually meant power supply. I am not sure if its an actual battery or (as someone else has mentioned) a capacitor (I suspect its actaully a capacitor).
If the power fails and the control panel battery is OK, then I would guess that the control panel will still be providing power to the bell box, which will still charge the capacitor. When the control panel battery eventually dies, the capacitor will power the bell box, which will annoy the neighbours!
Alan
Mine has a timer to meet these regs, but I guess a capacitor value selected against the known current drain would have the same effect, though it might be difficult to convince a jobsworth with a stopwatch of this.
I think you're supposed to provide the constabulary with either the name of someone they can call to turn it off in your absence (since they don't respond to alarms not connected to a call centre without some other evidence), or your keys so that they can do it themselves. I wonder how many people have done either, especially the latter?
Chris
Aren't they supposed to turn themselves off after 20 minutes or so, like car alarms?
I see that boxes available on the web have an auto cut-off timer. Mine is a good few years old so do you know if regs would require retrofit or is it only for new installs?
Tony
In message , Peter Johnson wrote
In this case the alarm wasn't triggered normally.
The time-out is implemented in the control box which has no power because the backup battery is dead. The bell rings because of the anti tamper circuit. Remove power from the wires supplying the bell box and a relay (mechanical or solid state) trips and applies the power from the back-up battery in the bell box to the bell.
If the battery in the control box were okay the alarm wouldn't have normally triggered in the first place and even if it had a time-out would have cut in.
On my 15 year old system the time-out period is configured by the user during the programming mode of operation. I've set mine to 5 minutes for the bell. The strobe light continues until reset by the user.
Usually 12v SLA. Available from Maplin's or any good alarm company. Min'e about 10 years old and held up all day recently whilst the CU was replaced^Wrepaired.
A new battery should hold up for a day at least, unless the panel is alarming.
The bell box battery is usually a nicad (or possibly NiMH in newre boxes).
I have hidden switches to (individually) disable the bell box batteries (no the second bell box /isn't/ a dummy) without having to get out a ladder, following a need to at some unearthly hour some time ago.
My panel pre-dates the regs, but has a programmable delay which is set to meet the requirements.
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