Tech Tips: What Size Power Supply?

21 Oct, 2020, 10:58 AM

One of the more common questions I get asked is what size power supply is needed for.


Below is a list of common items and their approximate power requirements at 12v DC:-


*** Please remember that all values are approximate only ***

Product Type Power Supply
Magnetic locks 500mA
Electric strikes 250mA
Mortice locks 250mA
Drop bolts up to 1amp
Prox readers up to 100mA
LED indicator 15mA
CCTV Camera 250mA
Top hat piezo 110mA
DC Siren up to 350mA
Bulldog dual screamer max 500mA Strobe 150mA
Sonalert buzzer 20mA
Codepads 35mA-100mA +
Dualtec 25mA


Dry contact, or relay contact this is a straight switch output, it has no voltage associated with it, the required voltage must be supplied to one side of the contact.


Open Collector this type of output switches to a reference voltage, most commonly it switches to negative. With this type of output the driven device (eg siren) is wired so that the negative side of the device is connected to the output, and the other side to permanent positive. These types of output are typically rated at 1Amp, 500mA, or 100mA.



Always allow 25% greater power supply capacity to cater for equipment variation and real.