Sending power down a long cable - RF Cafe Forums

 Post subject: Sending power down a long cable

Posted: Thu Feb 16, 2006 3:17 pm 

Hello,

My friend (really, not I) just did a home security camera system installation and he did a pretty thorough job of violating all the instructions that came with it. It barely works at all. After just a quick look, it appears the main problem is that he used cables WAY too long for the job. Instructions say don't exceed 150' and he used almost 1000' for one camera that runs to the end of a boat dock.

I measured the voltage at the camera end and it is about 10V (60 Hz, I assume). The transformer at the control box is at about 12.5V. The camera spec goes down to 10V, so it's right on the edge. The picture must be transmitted back over the power lines, because there is only a twisted pair feeding it. The picture quality (when it works at all) is about that of an Apollo moon landing transmission. Odd thing is it works best in low light conditions, and it works fine when on 100' or so of cable.

Looks to me like a transformer is in order on the long line, but where do you get one that steps 10V up to 12V? Radio Shack doesn't carry one. Any thoughts/suggestions?

- Regards

 Post subject: Sendind power down a long cable

Posted: Fri Feb 17, 2006 6:32 pm 

Are you sure the problem is due to a voltage drop? It could be signal degradation on the line. You did not give any specifics about the cable or the signal.

 Post subject:

Posted: Tue Feb 21, 2006 8:40 am 

Thanks Joe.

The cable is a nothing special twisted pair of what looks like maybe 20 ga. stranded. No shield over the pair. I can see it working OK over 100 feet or so, but 1000 just seems to be pushing it.

How long do telephone line twisted pair normally run between amplifiers? I've never taken the time to look that up.


- Regards

 Post subject: sending power down a long cable

Posted: Tue Feb 21, 2006 6:33 pm 

Sounds like the problem is the signal. The power level out is too low.

This is probably similar to DSL, which typically has a range of a few miles. The camera is not likely to have the same output power as the DSL modem. This would mean far less range. If the manufacturer calls out a range of 100 ft, it can probably do a little more, maybe 150 ft. 1000 ft. is too much.

You could try an in-line amp designed for DSL. This may increase the range. Keep in mind you still need to get the 12v to the camera. Ideally you could find an amp that will pass the dc. If not, you could use bias tees to get the voltage around the amp to the camera.

 Post subject:

Posted: Fri Mar 03, 2006 9:10 am 

I had the same problem with a cheap surveillance system I purchased. Definitely do not exceed the length of cable they give you. I believe the systems are marginally designed. Even with a relatively small house, it is easy to use up close to 200 feet of cable by the time you route it through your attic, under the house, down walls, etc. I would prefer wireless, but do not want to have to have a power outlet near each sensor (nor buy batteries).

Rule of thumb: Read directions. Follow directions.

 Post subject: Video and Power 1000 feet over CAT-5 Cable

Posted: Sun Apr 02, 2006 12:08 am 

I have successfully installed a number of video surveillance cameras up to 1200 feet from the monitor/power supply using CAT-5 twisted-pair wire.
Several suppliers offer small adapter units to place at each end of the CAT-5 cable to feed DC to the camera and receive video back to the monitor. Check out www.supercuircits.com. The main problem with CAT-5 is that its' DC resistance is approximately 30 ohms/1000 feet. This means that there is 30 ohms in the DC feed wire going TO the camera and 30 ohms in the DC return.

It is possible to modify the adaptor modules so that spare pairs of wire are paralleled in order to cut the resistance in half.

I solved the problem of excessive voltage drop by using a power supply with a higher voltage output and installing a simple little 3-terminal regulator at the camera to drop any excessive voltage back down to the required 12VDC. Whatever you do, calculate the voltage drop based on the total resistance in your CAT-5 run and use a power supply that puts out 5 to 8 volts above that and let the 3-terminal regulator drop the voltage at the camera site back down to the required level.

The video coming back from a 1200 foot run of CAT-5 cable is just a tad soft from high-frequency roll-off, but is still at least as sharp as a the video playback from a typical VHS video tape cassette player.

MPB
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