Connect with us

direct current loss per foot of wire

Discussion in 'Electronic Basics' started by servozoom, Nov 28, 2005.

Scroll to continue with content
  1. servozoom

    servozoom Guest

    I can't seem to find an answer to this question anywhere, So I've
    come to the experts. I need to power a device that requires 500ma of
    12v dc current, but it has to be 200 feet away from the transformer.
    Will a 1amp power supply provide adequate current over a 14 gauge wire?
    Is there a formula to figure this out? Thanks in advance

    Nick (servozoom)
     
  2. You can find many tables of wire data through Google, like this one:
    http://www.pupman.com/listarchives/1998/April/msg00189.html

    It lists the ohms per 1000 feet (ohms /Kft) and feet feet per ohm for
    many wire gauges. You should be able to apply Ohm's law to some
    possibilities and figure out how much of your 12 volts will get lost
    in the wire, out and back.
     
  3. Figaro

    Figaro Guest

    |I can't seem to find an answer to this question anywhere, So I've
    | come to the experts. I need to power a device that requires 500ma of
    | 12v dc current, but it has to be 200 feet away from the transformer.
    | Will a 1amp power supply provide adequate current over a 14 gauge wire?
    | Is there a formula to figure this out? Thanks in advance
    |
    | Nick (servozoom)
    |

    ---------------------------------------------------------------------------

    See http://www.epanorama.net/documents/wiring/wire_resistance.html section
    on Current Ratings

    V = DIR/1000

    D = 400 feet (200 feet x 2 round trip)
    I = 0.5 amps
    R = 2.575 ohms per 1000 feet

    then V = 0.52 volts = voltage drop

    your power supply must be 12.52 volts so that the voltage at the far end
    device will be 12.0 volts
     
  4. purplefloyd

    purplefloyd Guest

    Thanks so much to everyone, outstanding info, John's chart is a keeper,
    and Figaro's calculation made my job much less painless. You guys are
    the best.
     
  5. me

    me Guest

    Oh boy, where do we even begin:

    This question is impossible to answer because you don't provide useful
    information. First there's a question of your power source and then
    there's a question of your load.

    You claim you are 200 feet away from the transformer and then talk about
    a 1 amp power supply. So do you mean a 1 amp wallwart? You can't put DC
    into a transformer so you'd have to rectify it on the output of the
    transformer, it would also be a good idea to regulate it. You also don't
    state what voltage is acceptable at the load. 12V +/- what? Bare in mind
    that wallwart voltage tends to go all over the place depending on the
    load and they are unregulated.

    14 gauge wire has a resistance of .00297 ohms per foot (assuming copper
    wire, and room temperature, resistance goes up with temperature), so 200
    feet of it * 500mA gives you about .3V of drop. That means the voltage at
    the output of the transformer must be at least .3V above what you need at
    the load.
     
  6. servozoom

    servozoom Guest

    Thanks for all the info, I understand the problem much better.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-