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servozoom
Guest
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 Posted:
Mon Nov 28, 2005 9:35 am Post subject:
direct current loss per foot of wire |
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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)
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Figaro
Guest
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Mon Nov 28, 2005 9:35 am Post subject:
Re: direct current loss per foot of wire |
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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 |
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purplefloyd
Guest
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Mon Nov 28, 2005 9:35 am Post subject:
Re: direct current loss per foot of wire |
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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.
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John Popelish
Guest
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| Posted:
Mon Nov 28, 2005 9:35 am Post subject:
Re: direct current loss per foot of wire |
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servozoom wrote:
| Quote: | 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
|
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. |
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me
Guest
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| Posted:
Fri Dec 02, 2005 10:45 pm Post subject:
Re: direct current loss per foot of wire |
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servozoom <servozoom@peoplepc.com> wrote:
| Quote: | 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
|
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. |
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servozoom
Guest
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| Posted:
Sat Dec 03, 2005 1:35 am Post subject:
Re: direct current loss per foot of wire |
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| Thanks for all the info, I understand the problem much better. |
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neon
Joined: 25 Feb 2006
Posts: 579
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Wed Jul 26, 2006 11:20 am Post subject:
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| you got no answer i am afraid what kind of wire, solid stranded, how many strands all of those things make a conductor more or less.And most of what gauge. |
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