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700mA DC max range

Discussion in 'Electronic Design' started by [email protected], Apr 17, 2007.

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  1. Guest

    Hi all, wondered if anyone here can help me. I am runniing a camera
    which operates on DC12v @750mA. What would be the maximum distance i
    could run the cable, the cable i am using is rated at 5A.could do with
    a formula for this to work it out for my self... Cheers
  2. Phil Allison

    Phil Allison Guest


    ** The cable's max amp rating is not directly relevant to distance of the
    allowable run.

    You need to know the cable's resistance per metre and the allowable voltage

    Or, just try it out and see.

    ......... Phil
  3. Guest

    Thanks for your speedy response Phil. I have put a request into the
    company who supply the cable, just waiting for an email from them
    about the impedance. The run needs to be about 200 meters ideally and
    i'm just concerned that the setup will be dangerous if i use DC

    thanks Again
  4. Phil Allison

    Phil Allison Guest

    ** Err - so you have no ohm meter ?

    ** It won't be dangerous at 12 volts - just useless.

    You will HAVE to use a higher voltage - preferably AC.

    ........ Phil
  5. jasen

    jasen Guest

    there's no maximum especially if you're prepared to put a more than
    12V into one end provide voltage regulation at the camera end

    say amybe upto 24V in and a well-heatsinked LM7812 at the camera end
    we really need to know the resistance of the wire, (or its cross-section,
    or wire gauge - you want 200m, right?)

  6. Guest

    I have all the tools, just have not got the cable or power supply yet.
    if the run is too long wont the cable become hot?
  7. Phil Allison

    Phil Allison Guest

    *** Beware !!!!!!

    Google Groups ASININE LUNATIC loose on newsgroup !!!

    ** ROTFLMAO !!!

    What a BLOODY HOOT !!!!

    ......... Phil
  8. Dave Pollum

    Dave Pollum Guest

    This is basics electronics stuff - Ohm's law: E = I * R. So if your
    cable's DC resistance is 1.33 ohms, the cable's voltage drop will be 1
    volt. This means that if your 12v @750mA supply is at one end of the
    cable, then only 11 volts will be available at the other (camera) end
    of the cable. According to Alpha Wire's web site (, 10
    awg SOLID wire has a resistance of 3.4 ohms per km. This is 0.68 ohms
    for 200 meters. The cable's voltage drop is 1.02 volts (400m there
    and back). This is basically heavy duty house wire, rated for
    ~30Amps. And still, there is only 11 volts for the camera.

    As Phil mentioned, you will need a higher voltage at the non-camera
    end of the cable, preferrably AC. Move the power supply to the camera
    end of the cable. Then you can use a smaller cable.
    Why do you need 200m of cable???

    HTH -Dave Pollum
  9. Phil Allison

    Phil Allison Guest

    "Dave Pollum"

    ** Use your IQ - Dave.

    Google Groups Scum never reveal their real identities or purpose for fear of
    police charges.

    Likely, the " hot babe" this asinine fucking wanker wants to stalk lives
    about 200m from his bedroom.

    Nothing is innocent or simple on usenet.

    Or in real life.

    ....... Phil
  10. jasen

    jasen Guest

    no, because it is long the heat will be dispersed along its length.

    for example 20W dissipated by a 200m cable is 0.1w per metre or
    1mw per cm.

    If the cable is rated for 5A the any current less than 5A should not be an

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