alarm batteries

Just had a power cut (70 minutes not too bad a fix time for an 11kV fault I suppose)
OK, I did have to get up to silence the UPS (also shut down a couple of unnecessary PCs while at it to extend runtime)
But most annoying is the 15 minutes of alarms sounding due to failed batteries, then sounding again for another 15 minutes when the power comes back ...
People seem to think this is normal/acceptable ...
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Didn’t get that alarm result here. We had a deliberate power cut a week ago to change two power poles that lasted about 3 hours and no alarms went off on the cut or the restore.
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On 07/10/2019 05:30, Andy Burns wrote:

No, that's why I change my battery in my alarm every 3 years.
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Crikey. A decent SLA in such a friendly environment should last a lot longer than that. Got 11 years out of one car battery.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman wrote:

Some people must have had batteries replaced as I only heard one alarm last night, when we had a power-cut this summer (windows wide open) there were several to contend with.
I phoned-in the outage after giving it a couple of minutes (and a couple of failed attempts at cutting back in) the 105 reporting line automatically got my postcode from somewhere and recorded the outage, which appeared on WPD's fault map shortly afterwards, just had a call back from them to apologise ...
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On 07/10/2019 11:09, Dave Plowman (News) wrote:

It isn't all that benign an environment especially for the external bell battery in the external sounder. Being on float charge ready to go kills them in 3-5 years. Worth testing before swapping out though.
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Martin Brown
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I was assuming it was a faulty one in the panel which would cause the alarm to go off if mains lost?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 07/10/2019 11:09, Dave Plowman (News) wrote:

The problem in alarm panels is the battery is never cycled - just trickle charged 100% of the time. After a number of years the battery still has the correct terminal voltage but cannot provide the instantaneous backup power when the mains fails. As a result there is a glitch in the power to the alarm panel and the alarm is triggered. The backup batteries still can supply enough power for the sounders/lights for a long time etc. Checking the battery afterwards will again show the correct terminal voltage. You may only see the problem for the first time is when the mains power fails.
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Is this a pet theory or can you provide links to this battery behaviour? Sounds unlikely to me.

Um, you do know that the external sounder and strobe are additionally powered by a second non-rechargeable battery? Usually lithium I believe. There’s no need to postulate a “sluggish battery” theory. The voltage from the duff battery is just too low to run the system when there’s a power cut and this triggers the tamper circuitry.
Tim
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On 07/10/2019 18:06, Tim+ wrote:

My bell box has a rechargeable battery that is also trickle charged in my wired system via the alarm panel. My bell box also has red flashing LEDs so a self contained non-rechargeable battery may not last that long.
The tamper circuit in a bell box is often a spring loaded mechanical switch which when the box is removed from the wall is activated.

The bell box battery doesn't power the alarm panel which, in my case, has its own loud sounder.
Once triggered by a power cut the alarm can be disabled and run normally from the old battery which you suggest has a voltage too low to run the system.
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On Mon, 7 Oct 2019 19:38:11 +0100, alan_m wrote:

additionally

The bell box is normally powered from the panel to keep rechargeables charged or flash pretty lights. It also "holds off" the sounder and/or strobe. If the panel voltage drops to low, the sounder and strobe trigger and run from the battery in the bell box. Once this is triggered I'd expct it to run for several minutes before trying to reset and retrigger if the panel volts are still low/abscent. You don't want a scrote to be able to shut up the sounder simply by feeding it volts from another source...

And hopefully the cover... this should trigger a full tamper alarm condition. Which may or may not cause the sounder/strobe to be triggered.

Voltage too low when the sounder and strobe are drawing power...
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On 07/10/2019 21:24, Dave Liquorice wrote:

Commonly adjustable from 1 minute to 20 minutes (the legal maximum). Some also limit the number of re-triggers, while more basic ones don't.

They can do that, but usually the wiring comes through the wall from inside the house, so they'd need to be inside or they'd have to pull the box off the wall or open it first (either of which triggers them immediately). Far easier and quieter to squirt foam inside.

Usually it would directly trigger the sounder/strobe of the bell box, without needing the alarm panel to signal one and then it'd continue to run on its internal battery. It would also give a tamper alert at the panel, which may well no longer have a sounder/strobe connected, but as its going off anyway, that doesn't matter.
SteveW
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I thought the bell box battery is only there so it will sound if it or the wiring to it is tampered with. Under other circumstances, the panel supplies the ringing volts to it - either from mains or its battery.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 08/10/2019 11:20, Dave Plowman (News) wrote:

Self Actuating Bells do not ring when voltage is supplied from the panel. The 12v from the panel stops them ringing and charges the battery.
When an alarm condition exists the 12V is removed and they bell rings until it comes back or the battery goes flat or if its a modern one a timer expires.
Only cheap and nasty DIY alarms need 12V to operate the bell. If you have one then get rid of it as it takes seconds to cut the wires and then there is no external bell.
The old fashioned strobes may be powered from the box, mine are, they take too much power for the battery.
Its not the same 12V that operates the rest of the box.
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OK.

But if you remove the 12v the sounder sounds?
No expert on alarm internals since I've only ever followed a wiring diagram. But with your method, it would mean the sounder no longer works if the internal battery is kaput?

Thing is the bell box should be situated where it's difficult to get at. Which means changing it or the battery equally difficult?
And anyone who feeds it with accessible cabling should be shot. ;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 09/10/2019 10:26, Dave Plowman (News) wrote:

It does on a decent one.

That's why you can test them.
Its how all the bell boxes on banks work so it can't be the worst way. No banks use one that rings when it is powered by 12v in an alarm condition.
I have actually installed some for Chubb alarms but it was a long time ago and I quit as I didn't like the training bloke as he was getting things wrong about mains and didn't like being corrected.
It was my first proper job before I moved the GEC telecomms.

The battery is fine for years. Not all buildings have somewhere difficult to get to.

crowbar, rip box off wall cut wires and one that needs power from the panel goes quiet.
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Handy for a can of foam, then?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 09/10/2019 14:15, Dave Plowman (News) wrote:

When chubb fitted real bells they had a special box specifically made to stop expanding foam from getting in. They were the triangular ones. I won't comment on what they did as they may still use them for all I know.
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On 09/10/2019 12:33, dennis@home wrote:

Both SABs and SCBs should still ring if ripped from the wall.
It would also set of the internal alarm and any other bell boxes.
It's also a good bet that it would also set off an alarm signal to a monitoring company.
BTW cutting the telephone wires on a proper monitored system also actives the monitoring company.
Mind you opening one door without first closing another door on an unset alarm can also set of a silent alarm in some houses BTDTGTTS. The police were there in about 3 minutes.
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Adam

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On Wednesday, 9 October 2019 21:00:38 UTC+1, ARW wrote:

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How will that work when it becomes snap the fibre?
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