Voltage drop on cable run

[jimbouk]

Trying to install a cctv camera using shotgun cable, coax and power combined. CCTV element fine but the voltage drops from 12.1 volts going into the cable to 8.3 volts coming out, not enough to power the camera...

Anyone know what I need to put in to get 12volts out? Yes it is a long cable!

Thanks

Edited by jimbouk on Saturday 15th January 19:02

[Piersman2]

jimbouk said:

Edited by jimbouk on Saturday 15th January 18:56

Must be high as none of your keyboard voltage made it to the motherboard!

[jimbouk]

I was trying to move the post to DIY section using an iphone.... failed at that too!

[headcase]

Make sure your connections are good, if your dropping 4v over that cable run then it makes sence to add 4v to the supply, so try 16v.

[Driller]

How long is your cable exactly? One of my cameras is on a shotgun cable of beteen 40-50m and it works fine if that helps. I agree that it sounds like a contact problem.

Did you solder anything?

[jimbouk]

Thanks for the suggestions. Cable is probably 50m long. Have 5 runs if similar length and they all have the same issue. Some if the others I gave resolved with a local power source, not possible with this camera location though. Unfortunately the cables were all installed within the fabric of the house during a major refurb 4 years ago, without the option to easily replace.

Joints between transformer and cable are done using a strip block connector, Is soldering a better option.?

Got an old 19v laptop transformer, might see what that does.....

[Driller]

jimbouk said:

Joints between transformer and cable are done using a strip block connector, Is soldering a better option.?

Got an old 19v laptop transformer, might see what that does.....

I just wondered if you might have a bad solder joint but obviously that's not the case.

Are all your cameras running off one power supply? If so I would try a single 12v 1A supply to see what happens. Unless your cameras have a voltage range up to 19V I wouldn't risk more than the 16v that Headcase suggested.

[headcase]

Unless the cameras run from a regulated PSU you will find they will accept a large swing in voltage, I would of thought 19v regulated would be ok as it will drop to 15v over your cable run and 15v should be well within the spec of the camera. You could of course make your self up a little black box with a 7812 voltage reg inside and have that mounted on/near the camera.

[The Moose]

I have to say, I would be bloody careful doing that - CCTV cameras are generally sensitive pieces of electronic equipment and even 19V can screw one up a fair bit (I should know - I did the same thing!).

I would imagine your camera will be 12v (not a range) and the power supply will have a range of input values?

As I said - just be careful...and good luck!

Cheers

The Moose

ETA: I have to admit that I am surprised that over 50m you are getting that much voltage drop? Even on crappy quality cable I haven't experienced enough voltage drop at 50m to stop a camera working...it will depend on the exact spec of the camera, the cable, the PSU etc

Edited by The Moose on Tuesday 18th January 11:56

[VEX]

I would check the psu is giving 12v. Most cheap ones are unregulated so if they have little current draw they will run higher than that.

Also as has been said, try with just one camera at a time, it could be that the draw of all your cameras is to great for the psu, which is why it is under driving.

V.

[TonyRPH]

It sounds as though your cable is too thin, and therefore dropping too much voltage for the amount of current drawn.

A simple test would be to apply 12v on the power end, and then put a small 12v bulb where the camera resides. (*with the camera disconnected)

Then measure the voltage*.

Use a sidelight bulb from a car - they are usually around 12w which will draw 1 amp.

Could also try an indicator bulb (21w) which will draw just under 2 amps.

Measure the voltage in both instances - if you see a substantial drop with either (but particularly the 21w bulb) then your cable is simply too thin.

The solution would be to up the voltage as suggested above - but be careful you don't exceed the rated voltage of the camera.

For what it's worth.. if you are dropping a lot of voltage across the cable, it will be acting as a very, very low powered heater...

Edited by TonyRPH on Tuesday 18th January 20:12