# 700mA DC max range

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

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 AllisonGuest

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** 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
loss.

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
voltage.

thanks Again
Dan

4. ### Phil AllisonGuest

** 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. ### jasenGuest

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?)

Bye.
Jasen

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 AllisonGuest

*** Beware !!!!!!

Google Groups ASININE LUNATIC loose on newsgroup !!!

** ROTFLMAO !!!

What a BLOODY HOOT !!!!

......... Phil

8. ### Dave PollumGuest

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 (alphawire.com), 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 AllisonGuest

"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

Nothing is innocent or simple on usenet.

Or in real life.

....... Phil

10. ### jasenGuest

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
issue.

Bye.
Jasen