On 16/02/2019 07:35, Tim+ wrote:
alan_m wrote:
On 15/02/2019 14:58, DerbyBorn wrote:
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?


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.

Interesting theory but wrong.

Old batteries dont get €œslow€� 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 €œtamper€�. The
sounder/strobe has its own battery that can keep the sounder going for ages
without any external supply. Its got nothing to do with the main battery
€œrecovering€�.

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.

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