For some reasone I have a Burglar Alarm serviced every year - it is wireless.
The guy usually puts a voltmeter on the various batteries and usually declares them okay for another year.
I would thing the no-load voltage is a poor indication of likely life. Am I right?
no.
Poor indication.
In my mains powered alarm base unit a "failed" battery will still show the correct terminal voltage. What it will fail to do is provide enough instantaneous power in the event of a power cut. The mains will cut out, the backup battery will not cut in fast enough and the alarm will trigger. The battery will then recover enough to leave the alarm in the triggered state with the strobe flashing and the horn sounding. Unfortunately you may not realise that the battery is on its way out until you get a power cut.
I stick a label on my alarm box detailing when I last changed the battery and I replace it after around 3 years.
Is there a reason for getting your alarm serviced this way each year? As this a DIY group I'm sure that you could have a routine to replace the batteries every so often. The money saved by declaring an alarm on for insurance is minimal.
I frequently test batteries for mobility scooters.I've found that a no load voltage test isn't much help. I therefore do a discharge test. It doesn't actually take long for a poor battery to reveal itself. But in the case of alarms I would be inclined to replace routinely every three years.
Bill
My DVM has a setting for no-load voltage measurement, and a different setting for battery testing. In the latter case, AIUI some load is put on the battery, i.e. current is drawn, and the voltage reading will fall away quite quickly if the battery is on its last legs. Perhaps your guy has such a setting on his meter.
DerbyBorn explained on 15/02/2019 :
Yes, it is pointless - even off charge it takes a while for battery volts to fall. The proper test method is a drop test - a suitable load is applied and then the voltage monitored, for a rough idea.
Chris Hogg presented the following explanation :
Those good for small primary batteries, but not much use for a lead acid battery - the tiny discharge will not really affect the voltage much.
I was conerned about my wife coping with my home installed alarm when I pop my clogs. I did have a mains powered one I installed myself - a kitchen extension made it necessary to change it.
Interesting theory but wrong.
Old batteries don?t get ?slow? or then recover to provide power for the sounder etc.
When the mains goes, they fail to provide enough power for the system and the external sounder/strobe responds to this as a ?tamper?. The sounder/strobe has its own battery that can keep the sounder going for ages without any external supply. It?s got nothing to do with the main battery ?recovering?.
Tim
Are they rechargeable?
I would have thought that a realistic load and voltage drop measurement might be a good idea, certainly. I have an old laptop where the battery reads fine after a charge, for all of five minutes in use! Brian
Yes, the bell box may detect a a short drop of power as a tamper but battery is still well enough to allow the control unit to be fully working to cancel the alarm.
While the battery in the control unit may be replaced at regular intervals I wonder how may batteries in the bell box are replaced likewise?
In an alarm system batteries tend to never go through a discharge cycle unless there is a power cut.
For a mains powered panel:
If the mains supply is still on, he's measuring the charging voltage
- pointless.
If the mains is off, he measuring the voltage under load. If he's measures it immediatly after the mains is switched off and again 10 mins later the difference will give a reasonable indication of the state of the battery.
For the sensors they take very little energy, what are the batteries? Tewrminal voltage might be good enough. I'd assume that there is some method that gives a low battery warning for a given sensor.
"Dave Liquorice" snipped-for-privacy@howhill.com wrote in news: snipped-for-privacy@news.individual.net:
CR123 BATTERIES - in the sensors.
Surely if its an expensive maintenance contract any non-rechargeable batteries probably should be replaced yearly to ensure that the system works reliably for a future 12 months?
That would be a bit of an expensive waste, especially if the likely lifetime is about 10 years for a lightly loaded lithium primary cell.
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