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?
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.
The transformer should have a current rating on it somewhere. Use that figure with the length you need to calculate the voltage drop. A
10% drop wouldn't normally cause any problems
For example. 0.5 square mm cable (that is 3amp mains flex) has a resistance of 38ohms per kilometre. If you have a 50 metre run that is a loop resistance of 3.8 ohms. At 100mA that would be a drop of
0.38 volts which wouldn't matter. At 1 amp it would be a drop of 3.8 volts which probably would 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.
In article , dcbwhaley writes: |> |> The transformer should have a current rating on it somewhere. Use |> that figure with the length you need to calculate the voltage drop. A |> 10% drop wouldn't normally cause any problems |> |> For example. 0.5 square mm cable (that is 3amp mains flex) has a |> resistance of 38ohms per kilometre. If you have a 50 metre run that |> is a loop resistance of 3.8 ohms. At 100mA that would be a drop of |> 0.38 volts which wouldn't matter. At 1 amp it would be a drop of 3.8 |> volts which probably would be a problem
If you need heavy cable, remember that vehicle electrics have the same problem. I was trying (and failing) to fix a fault in my car's harness, and some of the wires are much thicker than any domestic mains cable. I assume that you can still buy such wire.
Ive got a camera with 6 IR leds on about 30M of .75mm 3 core screened flex, had it lying around. Biggest drain in a camera think is probably the LEDs, some have a small wirewound resistor that is meant to act as a heater to stop misting. Speaker cable is a good low cost cable for the power and RG58/59 is lot thinner than standard coax if you need to extend the signal.
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