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Tell
Me More About Alarm System Power Supplies
Electrical
Power Transformers
The transformer converts the 120 Volt AC power in your building
to 16 Volts AC to meet the requirements of the alarm control
panel. The typical size of transformer used is 37VA which
limits the current used by the system to less than that of
a 40 Watt light bulb. Most of the time the system will draw
considerably less than this.
The
transformer should be connected to a source of 120V AC power.
This should be fed from a circuit that can only be shut off
from the breaker panel (not from a light switch). There are
two types of transformer, wire-in and plug-in. Wire-in transformers
are preferred because they are more durable and are less likely
to be accidentally disconnected. Plug-in transformers look
like a small plastic box about 2" by 3" in size
and plug in to a standard power outlet. They are sometimes
used when there is no place that a plug-in transformer can
be mounted.
Quality
Alarms uses wire-in transformers (manufactured by ATC-Frost
in Canada) whenever possible. We have found that they are
quieter (some transformers actually buzz) and are significantly
more reliable than the cheaper off-shore models typically
used in alarm systems.
All
points in the system after the power transformers are deemed
to be "low voltage". These voltage levels will not
"shock" you if you come into contact with them.
This means that all system wiring can be done using small,
low cost, telephone or “data” type cables.
Low
Voltage Power Supply
Modern alarm panels include fairly sophisticated low voltage
power supplies. The power supply converts the 16 Volts AC
supplied by the transformer to 12 Volts DC (or 13.8 Volts
to be more precise). This is used to power the control panel
circuit board and all other system devices as well as recharge
the backup battery.
The
alarm control panel can detect the presence of AC power and
automatically tests the backup battery to make sure it is
fully charged and operational. If there is a problem with
any part of the power supply the alarm keypads will alert
you and indicate the type of problem that has occurred.
The
power supply includes circuit protection to prevent a short
or overload from damaging the control panel. There are even
separate feeds from the power supply that assure that the
system will still be able to report an alarm to the monitoring
station even if an intruder shorts out the power wires feeding
the alarm siren, keypad or system sensors.
Backup
Battery
All alarm systems are supplied with a "gel-cell"
backup battery that allows the system to continue to operate
during a power failure. The manufacturer of the system will
recommend the size of battery although this is largely based
on the number and type of devices connected to the control
panel. A typical battery size is 7AH (AH = Amp Hours). This
means that the battery can provide 1 amp of power at 12 Volts
DC for 7 hours when the battery is in good condition. A typical
alarm system will last about 12 hours with a 7AH battery.
On a very small system a 4AH battery can sometimes be used.
A
backup battery normally lasts about 3 to 4 years before it
needs to be changed. A properly designed alarm system will
let you know when it is time to change the battery by annunciating
a "trouble condition" on the alarm keypad. The battery
is housed inside the alarm control panel cabinet and is connected
using two slip-on connectors. It is a fact that your backup
battery will have to be changed at some point. You may want
to ask about the cost of replacing the backup battery when
you are speaking to alarm companies about purchasing a system.
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