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 With the various ways, manufactures spec their products for current draw, it is essential that a power supply of adequate amperage is used.
Having installations with multiple current draws for fire, security, CCTV and access control the power supply is the heart of it all and your guarantee of a successful and trouble free installation. The following information is to help you in determining an adequate power supply for your installation.
Power (Watts) =P
Current (Amps) =I
Voltage (Volt) =V
VA is power in Watts as used in AC circuits.
E.g.
1) A 60 Watt light bulb = 60 VA current draw.
Voltage will always be given however some manufacturers use Amps while others use VA ratings or Watts.
You will require one of these three formulas to calculate the missing variable.
P = I x V
I = P/V
V = P/I
2) Having a 12 Volt, 20 VA transformer, you need to determine the maximum allowable current draw.
I = P/V
I = 20/12
I = 1.666Amps
3) Given a 24 VDC system with 3 electric strikes that draw 110 milliamps each, 1 maglock that draws 280 milliamps and 4 keypads that draw 38 milliamps. What is the total current draw?
1000 Milliamps = 1 Amp
To determine the total current, you would add current draw of all the devices together.
I = .110+. 110+. 110+. 280+. 38+. 38+. 38+. 38
I = .762 Amps
As a rule, a safety factor of 25-50% is used to determine what current rating is required to safely power your system. Therefore we require a minimum 24 VDC .953 Amp power supply.
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