DIY Alarm Servicing Page 2:

!. Do not attempt to proceed unless your 100% confident in your abilities to complete any of the following tests, If you are at all unsure please seek out a professional .!

!. Please be very careful, there is always the potential of an Electric Shock when working with any mains powered device.!

Voltage Checks:

We are going to check that your control panel is supplying the correct voltages to its Battery, Bellbox and Detectors. So you'll need to have your Multimeter ready, and set to measure DC Voltage in a range that can measure from 10 volts and up to 20 volts. If your not sure how to use your Multimeter or are in any doubt as to whether the leads are in their correct locations then proceed no further as you may damage your panel or blow fuses etc........

Not all panel manufacturer's use the same terminologies so ill be using the most common as this will apply to the majority of panels.

• AUX Voltage: This is the point from which all your powered detectors will get there supply voltage from, make sure your Multimeter is set to measure up to 20 Volts DC and that your test leads are in the correct locations on your Multimeter. Place the black probe on the AUX- terminal and the red probe on the AUX+ terminal and record the voltage.
• SAB Voltage: This is the location from where the Bellbox is powered, and is normally referred to as the bellbox hold off's, place your black probe on the terminal marked Hold- and your red probe on the terminal marked Hold+ and again record the voltage.
• Battery Voltages: Here I'll want you to check the voltage at the battery terminals with the charging leads from your panel connected, and then at the charging leads with the battery disconnected. You should get 2 slightly different voltages from these two readings, with the 2nd reading being slightly higher. While your battery is disconnected check for a date of installation on the battery and if older than 5 years or if its terminals show any signs of damage or corrosion then fit a new one.

We are looking for all our voltage results to be within the range of 13 Volts to 14 Volts, and ideally not be at extremes from each other, by that I mean they should all be fairly close to each other, here's the results from my control panel just for a comparison purpose:

1. AUX Voltage: 13.79 Volts DC.
2. SAB Voltage: 13.78 Volts DC.
3. BATTERY Voltages: "Battery Connected" = 13.8 Volts, "Battery Removed" Charging Terminals only * = 13.82 Volts DC.

As you can see, there is not a lot of difference between any of the results I achieved, with differences being only a few 10th`s of a volt. The lowest recorded voltage was 13.78 volts and the highest was 13.82 Volts.

*If your control panel is fairly old or perhaps one of the cheaper models then these may vary quite a bit, but as a general rule I would still expect the lowest and highest readings to be within 1.5 volts of each other and not above or below 12.5 to 14.2 Volts.

Checking the Backup Battery:

Before we proceed here's a little info about the "Gel" type of battery used for backup power in your control panel:

Technically they are "Sealed Lead Acid" batteries, The cases are made from a non-conductive material usually consisting of ABS plastic, styrene or polypropylene. The "Gel" battery is a modification of the standard lead acid car battery. A gelling agent (often silica) is added to the electrolyte to reduce movement inside the battery case. Gel-Cell batteries are considered non-spill able, and can usually be used in any position except upside-down. They usually have a one-way valve acting as a vent for excess gases to escape. Gel-Cells must be charged at a lower current to prevent excess gas from damaging the cells. Fast charging them may permanently damage a Gel Battery. Connection points for power are usually the push on spade type of connectors on the lower amperage batteries, or screw and nut type of connection points for higher amperage batteries. Battery Capacity, is expressed in ampere-hour's (AH) and in the case of Gel batteries this is the total amount of energy available from a fully charged battery over a 20 hour period.

So a fully charged 7AH battery should supply 350mA FOR 20 hours, but if we increase that rate to 700mA it will doubtfully last 8 hours, when you would probably have expected it to last for 10 Hours. More info on Batteries.

Checking Standby Capacity:

To comply with British Standards your Alarm System should be able to function normally for periods of at least 8 hours in the event of a mains supply Power failure, so we will need to check the current draw of your control panel when in an un-set/standby condition.

You will need to set up your Multimeter to read DC Amp's in a setting capable of reading up to 1 Amp. And if you have them it would be wise to attach some crocodile clips to your multi-meter's test probes.

To check the current drawn by your system you will need to remove the positive battery lead from the backup battery, so that only the negative lead is still connected to the battery, your meter probes will then be connected so the black lead goes to the spare positive battery terminal, and the red lead to the spare positive battery lead. Your meter might now be reading a small charging current but this isn't what we want to measure, to measure the standby current we need to disconnect the mains supply from the control panel and this is simply done by removing the fuse from the un-switched fused spur that you should have fitted when installing the alarm. Now Read the measured current draw and when you have a steady reading re-fit the fuse into the fused spur and watch the reading to make sure it starts to go back down as the panel charges the battery. Now we can remove the tester probes and re-connect the red battery lead to the red battery terminal.

If all went well you should have a standby reading of anywhere between 75 and a few hundred mA, the standby current draw on my own alarm system was 315mA, which isn't to bad considering all that I have attached to it. Make a note of the Amp Hour rating on your battery and see the chart below.