On Sun, 24 Feb 2008 09:42:47 -0000, Roger Mills wrote:
In an earlier contribution to this discussion,
Mike Hibbert wrote:

Morning!

I'm looking to install CCTV at the front of the house (long story,
involving kids, eggs, and rather bizarrely, comedy penis's drawn in
butter on the car!)

I bought a camera which runs on 12v and comes with a transformer. But
the lead on the transformer is only about 7' long, which for an
outdoor camera makes it pretty hard to position and still plug in.

I have 3 options I guess, site it somewhere else, buy a new
transformer with a longer lead, or extend the existing one.

My question is, if I simply cut the cable and extend it, will there
be a noticeable drop off in voltage to the camera?

Cheers

Mike

I doubt it. How much current does the camera take? If you multiply the
current by the length of cable and by the resistance per metre of the cable
you intend to use, you can calculate the voltage drop. If you use suitable
cable it shouldn't be a problem.

Eggs, butter. Get the little B*****'s to flour-bomb you and you could make
a cake :-)

It sounds like the co-ax to the TV is long enough, already. is that so?

In practice you won't need to worry about current, length of cable etc. The
camera will be OK (It might even work better[1]) But make sure you do the
following:
- solder the extension wire, don't just twist the conductors together.
- use decent thickness bell-wire. It'll also be tougher than thin wire
so should withstand the outside environment better. Make sure your
joints are weatherproof. (Your camera is spec'd for external use?)
- consider making the cut in each conductor a cm. or two up/down from
each other, so they are staggered. That way any short-circuits will
be less likely to matter. It also helps with the next point:
- you *must* keep the same voltage on the same conductor. Normally one
will have a stripe on it. Do all the extension on one conductor, then
on the other. That way it'll be harder to mix 'em up. Afterwards
check that you're still getting positive volts on the same part of the
plug. If you mess this up, you'll probably destroy the camera.

[1] I have done some work with low-light CCTV cameras using Ex-view CCDs
(Very sensitive. Remember, B&W cameras are more sensitive than colour)
and I've found that dropping the supply voltage down from 12V to 9V
keeps the camera chip cooler, so the picture contains less noise. This
doesn't matter for daytime viewing, but gives a better picture at
night. YMMV.

Pete

--
.................................................. .........................
.. never trust a man who, when left alone ...... Pete Lynch .
.. in a room with a tea cosy ...... Marlow, England .
.. doesn't try it on (Billy Connolly) .....................................