# Calculating the power required for a video system

Discussion in 'The Projects Forum' started by RGL, Mar 16, 2015.

1. ### RGL Thread Starter New Member

Oct 14, 2008
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I’d like to apologies in advance if this has been answered in the past. I attempted several searches but could not find what I needed.

While I have 20+ years in electronic repair I have zero experience designing circuits.

I have been asked to determine the amount of output power required to operate three video cameras. Each camera will draw up to 7 watts when under full power. Each camera needs 1 watt and the camera heaters require 6 watts.

The output voltage provided by the display to each camera will be 10 VDC.

I also need to consider the cable length from display to camera, each being about 100 feet using 28 or 22 AWG multi strand copper wire.

My first thought is 21 watts by simply adding what is needed for each camera however when I consider the voltage drop along the cable I feel that may not be enough.

Any help would be appreciated.

2. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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For each camera @ 10V dissipating 7W will require 0.7Amps
Total current for 3 cams is 2.1Amps. That would be for all the camera.

It will be better if you power each cam separately rather than looping.

For 100 feet of cable, it is better to use thicker wires.

3. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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Size the wire based on the allowable voltage drop..
IMO 22/28AWG isn't going to cut it at all.. I'd think 14 AWG or so is more like it..

4. ### RGL Thread Starter New Member

Oct 14, 2008
3
0
Thanks for the input. I figured the 2.1 Amps as well and asked that the monitor power supply be capable of at least 28 watts to be on the safe side. As to the cable I should have mentioned the camera power is separate from the heater. The camera needs 100 mili amps and the heater needs 600. In that regard the voltage drop for camera power will be well within the +/- 3 volts even at 28 AWG. While the heater drop will be more it is irrelevant as it will only heat slower.

5. ### mcgyvr AAC Fanatic!

Oct 15, 2009
4,784
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^^ all good then

Jan 15, 2015
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Will it only heat slower or will the heater fail to reach or maintain operating temperature?

Ron

7. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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Both I guess.