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Quick Current Consumption Question

Discussion in 'Electronic Basics' started by CoogarXR, Jan 29, 2004.

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  1. CoogarXR

    CoogarXR Guest


    I have 2 cameras that have 12v 1000ma "wall warts". I have a 12v 4a regulated
    power supply that I would like to use in it's place. I plan to add more cameras
    to it some day, so the current will be a closer match, but for now my question
    is this: If I hook both cameras up to this power supply, will they draw only
    the current they need, or will the power supply damage the cameras by "forcing"
    the extra available current through them?

    I know this is a very basic question, but it has been many years since my
    electronics classes :)


  2. This is a very common beginner's question, and a perfectly legitimate one.
    Your 12V 4A power supply is able to supply 12V at *up to* 4A of current. The
    load will draw as much current as it needs (1A maximum per camera in your
    case). So the supply will provide a total of 2A to the combined load. Even
    if it was a 100A supply, it would still provide the exact same amount of 2A.
    For the supply to be able to "force" 4A through the load it *must* increase
    the voltage to a value higher than 12V (which it won't). As you can see,
    load voltage and current are closely linked, and this link is *independent*
    of the capabilities of the power supply. In resistive loads, the
    relationship between V and I is given by Ohm's law:

    V = I x R

    So, for a fixed load R, the voltage and current are linked together and
    nothing in the world can "force" a change in one without affecting the
    other. Your cameras are not entirely resistive loads and hence will not
    generally obey that law, but the idea is qualitatively similar.

    So, don't worry about the 4A supply rating. It just means it can support up
    to 4 cameras at the same time. Just make sure it's regulated and the
    connection/polarity is right - you don't want to fry your expensive cameras!

  3. CoogarXR

    CoogarXR Guest


    Thank you very much for your gentle and informative reply :)

    I had a hunch it was that way, I just didnt want to connect this new power
    supply and start fires all over the building when cameras start poppin'! hehe..

    Thanks Again,
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