I have been fielding a number of questions lately about power supplies. Do I need a power supply at each door that has an electrified lock? How many doors can I power from a single supply? Why do I need fused outputs for each door? There are several things to take into consideration when selecting a power supply.
VOLTAGE:
Most electrified locks will require either 12VDC or 24VDC. There are very few reasons why you would want to mix of 12VDC and 24VDC locks on the same project, so the first decision is the voltage you need. Power supplies are available in 12VDC, 24VDC, some are user selectable 12VDC or 24VDC, and a few are capable of simultaneously putting out both 12VDC and 24VDC.
AMPERAGE:
Each powered device will be rated for current draw. The sum of all of the devices is your maximum current requirement. It is normal to allow for an additional 20% capacity. The maximum current draw may or may not account for requirements for battery charging, which is why it is common to allow for some excess capacity.
EXAMPLE:
o 3 electric strikes @ .25 amps each = .75 amps (750 mA)
o 2 maglocks @ .15 amps each = .3 amps (300 mA)
o 2 motion detectors @ .05 amps each = .1 amps (100 mA)
The total current draw would be 1.15 amps. Allowing for an additional 20% would raise this to 1.38 amps, so your power supply selection will probably be 1.5 amps or larger.
OUTPUTS:
Power distribution boards are available from several power supply manufacturers to give you multiple outputs ranging from 2 to 16 outputs. These can be fused outputs, or PTC (polymeric positive temperature coefficient) outputs, with or without relay switching. In the example listed above with 3 electric strikes, 2 maglocks and 2 motion detectors, it would be easy to power everything off of one unprotected output. The advantage of using a power distribution board is you have a dedicated output for each device. When problems arise, it will make trouble shooting much easier. Also, when you have a problem with one device, it will not affect the rest of the system. It will be much easier to isolate, diagnose and repair the problem, while leaving all other equipment in service. It is typically a requirement to drop power to maglocks during a fire, so you also will want to make sure the selected power supply has a fire alarm input for this purpose.
MODELS AVAILABLE:
There are a variety of manufacturers that offer 12VDC, 24VDC, user selectable 12VDC or 24VDC, and dual output 12VDC and 24VDC. They can come as either linear or switching power supplies (the choice of linear vs. switching will be a separate installment on the blog) with current outputs from 1 amp to 20 amps and higher. Both fused and PTC outputs are available with 1 to 32 outputs, with and without relay control.
If you have any questions or need help in selecting the proper supply, our sales department is ready to help.
