12V DC Over CAT 5
NWCCTV
Posts: 3,629
I have an upcoming project that requires 12V DC @ 2 Amps running over CAT 5 cable. The problem is that the distance is about 300 feet and the voltage drop is way too much for the camera to work. Any ideas on how to "boost" this up to get the nominal voltage we need? I was thinking of possibly using a power over ethernet injector and just splitting the power side off but not sure that will work either.
Comments
run a separate power cable (of course), or just use a different cable in general.
double or triple up on conductors (use more than one pin for + and -)
use a power supply (usually the older linear ones) that has separate power sensing lines that will attempt to boost the incoming voltage so the other end of the cable has the correct voltage (requires a minimum of 4 conductors).
pump some other higher voltage down the cable and regulate it at the other end.
of course, don't hit the power limit of the cable, remember P = I^2 * R
Also, resistance is 28.6 ohms per 1000 feet (304 metres here in Australia - hey I just worked out why cat 5 comes in such a strange length!). So 300 feet is 3/10 of 28.6 which is 8.58 ohms.
2 amps drops V=IR = yikes, more than 12V. You are not getting much out the other end.
Hmm, 2A@12V is 24 watts. Say you are happy with 10% loss. So you can lose 2.4W. Hmm, let's try 48V DC. Now the current is only 0.5A. V=IR for the voltage drop is 8.58/2 which is 4.2V. Getting ball park here. W=IV loss which is 2.1W. Ok, can live with that. So at the other end, use a high input voltage switching regulator to step down the approx 44V to 12V.
Or run some thicker twin flex alongside the cat5. It may work out cheaper.