Has anyone seen this before?

[jldevlin 0]

I installed a security camera for a friend, I have installed 4 cameras at my cabin without issue...the system ran fine last week for 1 hur then the image went stupid, today I replaced the computer and again after an hour its screwy...have a look at the live image tonight and if any ideas are around to fix it let me know, my thoughts are a cable 75 ft long is too long and it started at tnight so when the infared lit up it sapped up what little power made it to the camera?

 

http://50.92.198.124:8181/multi.html

[SunnyKim 2]

75feet should be No Problem, whatever. Suspect power shortage to drive cameras at night, LEDs, IRs..

[GCoco 0]

As SK said 75 feet should not be a problem. Verify your power supply rating and compare to camera power consumption with IR on. I do not know what kind of cameras you have, but you need close to 1A or 12W power supply since Hiks typically draw 9W at night.

If the power is rated more than the camera rating, swap this PS with another, it may just be bad.

Also, you may have a bad cable/connector which in that case the problem will not go away. If swapping PSs that are rated high enough doesn't work, try running with a PS that plugs directly into camera. If problem goes away, replace your power cable.

[jldevlin 0]

The camera is working fine in the daylight now, I ran a test on the lines yesterday and they seemed fine, the camera is cheap as I am doing this for nothing for them, I will be getting a better camera for them, the ps has been changed several times as I bought 6 of them new with a 12v 1 amp rating....all seemed to have the same effect,possibly its the camera

[tomcctv 188]

Hi 1 amp is too low

[GCoco 0]

If camera is 9W or less, then a 12W is more than enough. What am I missing?

[jldevlin 0]

I have always used a 1 amp but that is what I was showed to use when a freind did mine years ago, now I see ones with 5amp 12 v, I will get it if they do not damage the camera? I assume not because they are for cctv camera

http://www.ebay.com/itm/8-Port-12V-5A-DC-Power-Adapter-for-IR-Security-Cameras-Zmodo-CCTV-SecurityDVR-/281578095208?hash=item418f5cc268:g:CoAAAOxyBjBTQ5XH

[GCoco 0]

You can use 1,000,000 A and it doesn't matter. The PS will only provide the power needed by the device being connected to it

[jldevlin 0]

I duplicated the issue at hand , I found it was definatly the cable length and power drop over that distance, I find a 40 ft cable will give me a good picture day and night,much longer and the night scene gets much worse....

[SunnyKim 2]

Good to know. DC Power does not go long on a very small diameter cable. AC power goes a lot longer. You better localize DC power source near cameras.

[GCoco 0]

For small conductors the AC and DC resistance are the same. On large conductors the AC resistance is higher due to the skin effect which does not allow correct to flow in the center of the conductor. That is why power lines use multi conductor wire so as to increase the surface area. DC current can flow through the entire conductor so for a same size large conductor you will have less resistance with DC than AC.

 

I am not discussing AC impedance (capacitance and inductance) since this does not become an issue over short distances.

 

For household AC and low voltage DC applications the DC resistance can be used to calculate voltage drop and the voltage drop will be identical whether you are using AC or DC for a given voltage.

[GCoco 0]

BTW 40 feet seems like a pretty short distance unless you are using an extremely small conductor.

18AWg wire has a resistance of 8 ohms/1000 feet. So a 50 foot run will have only (50+50)/1000 x 8 or 0.8 ohms resistance. For a 12VDC system, for every 12W of load, the voltage will drop 0.8V.

Hikvision 2232 with IR on will draw 9W, and the camera is guaranteed to operate at 10.8V. So using an 18AWG conductor the camera will operate at a distance of 100 feet. Actually it is lkely more since power supplies typically put out more than 12V and a typical home AC voltage is at least 123V.

[the toss 0]

For small conductors the AC and DC resistance are the same. On large conductors the AC resistance is higher due to the skin effect which does not allow correct to flow in the center of the conductor. That is why power lines use multi conductor wire so as to increase the surface area. DC current can flow through the entire conductor so for a same size large conductor you will have less resistance with DC than AC.

 

I am not discussing AC impedance (capacitance and inductance) since this does not become an issue over short distances.

 

For household AC and low voltage DC applications the DC resistance can be used to calculate voltage drop and the voltage drop will be identical whether you are using AC or DC for a given voltage.

 

 

Skin effect is virtually non existant at 50/60Hz and can be ignored

[GCoco 0]

For small conductors at low frequency (60Hz) you are correct.

 

The higher the frequency the greater impact the skin effect has on the resistance regardless of the conductor size. As the conductor size increases, even at 60Hz, the skin effect has a larger and larger impact on the resistance. Skin effect is a very important consideration in the transmission and distribution of electricity due to the large diameter of the conductors.

 

Skin effect is not important on small conductors since the skin effect is essentially non-existant due to the fact that the skin depth reaches to the center of the small diameter conductor, therefore AC = DC resistance.

[GCoco 0]

BTW I am a licensed professional electrical engineer with more than 34 years in the electric utility industry as a transmission and substation engineer.

[the toss 0]

BTW I am a licensed professional electrical engineer with more than 34 years in the electric utility industry as a transmission and substation engineer.

 

and I am a licensed proffessional RF engineer (with electrical engineering degree) specialising in microwave radio systems ( and where skin effect IS actually relevent ). I think you will find the multi conductor construction of your transmission lines is more to do with mechanical integrity than skin effect.

Skin effect isn't worth considering until you get to 500Mhz or so and it is more about signal propogation than power transfer

[GCoco 0]

https://www.anixter.com/content/dam/Anixter/Guide/7H0011X0_W&C_Tech_Handbook_Sec_07.pdf

 

See section 7.5 on the above link.

 

Conductors used in overhead lines use a steel core for mechanical strength and not the conductors themselves.

 

I have enjoyed this discussion, the purpose of which was to dispel the misconception stated in this thread that AC travels further than DC in wire. The toss is correct in his ascertain that for the purposes of this thread at 60Hz there is no difference.

 

But only this thread. Look at section 7.10 for a given conductor the AC/DC resistance ratio at 400 and 800 Hz. You will see a large increase in resistance at these frequencies. So the statement a skin effect isn't a factor until you get to 500MHz is not factual.

 

I stand by my previous statement that as the frequency or conductor size increases, so does the AC resistance. At 60Hz using small conductors AC = DC.

[the toss 0]

I guess the the real difference in our views is the environment we are thinking in. To me a long transmission line is 300m @9Ghz whereas to you a long transmission line might be 30Km @ 60Hz but since power transfer in an AC electrical distribution network is voltage driven & not current driven I still dont believe skin effect impacts as much as you say.

 

Skin Depth (>90% Cu) = Sq root of (2r divided by wu)

where r = resistivity w = angular frequency and u = permeability

 

skin depth = 8.5mm @ 60Hz

skin depth = 0.0066mm @ 100Mhz

 

as can be seen at 60Hz skin effect is of no consequence until the conductor is > 17mm dia.

 

Back to the original post and THE main reason to use 24Vac instead of 12Vdc is (just like in electrical distribution systems) the efficiency of power transfer - ie lower voltage drop due to current in a fixed resistance. It also enables voltage rectification & regulation at the load which will negate ANY voltage drop (within reason) over the transmission line