I have the dreaded horizontal rolling bars in my security cameras. I was able to resolve the problem by placing an old isolation transformer between the house wiring and the switching power supply that powers the cameras. The isolation transformer is just a huge heavy coil that is 120 in 120 out. It is something I had from taking electronics classes more than 30 years ago and like the transformer I'm rusty. I looked for a coil type transformer but couldn't find one that wasn't a few hundred dollars and designed for industrial use.

I have questions. Should I use the isolation transformer I have and if I do will it waste a lot of energy or have other downsides? If I need a new transformer where can I get one that will not cause the ground loop problem? Is there some other solution that is preferable?

Thanks

 

The problem with cctv hum bars, is the switch-mode psus, they "beat" with the switch mode in the monitor psu, i had this problem and sorted it out by swapping the monitor out.

What is it like with just one camera on the monitor?

 

The problem with cctv hum bars, is the switch-mode psus, they "beat" with the switch mode in the monitor psu, i had this problem and sorted it out by swapping the monitor out.

What is it like with just one camera on the monitor?

Hum is visible on my kindle and phones

 

Then its your psu that's causing it, do you have your cameras plugged into an hard drive recorder, which has its own 12V adapter, and the camers have their own psu?

Or do you have one psu and several cameras?

Could you draw a picture of your set up ?

 

Then its your psu that's causing it, do you have your cameras plugged into an hard drive recorder, which has its own 12V adapter, and the camers have their own psu?

Or do you have one psu and several cameras?

Could you draw a picture of your set up ?

It may be possible to simply add a bit more filtering to the DC supply for the camera. BUT, also, the power leads from the supply to the camera must not share the same common conductor as the shield on the video cable bringing the picture back to the monitor.

 

try a new Power supply they cost $15 or so. The capacitors go bad in them.
change both of them, the recorder and the cameras.

 

Then its your psu that's causing it, do you have your cameras plugged into an hard drive recorder, which has its own 12V adapter, and the camers have their own psu?

Or do you have one psu and several cameras?

Could you draw a picture of your set up ?

I have the switching power supply that came with the DVR and a seperate switching power supply that I'm using to power 4 cameras. They are both plugged into an extension cord. My room only has one outlet (house built in 1889 and original plaster so when I updated the electrical I was stingy). I tried a different power supply for a single camera which solved the problem for that camera but it was one of the heavy ones with a coil and only 200mA. The only wall pack power supplies I could find that would provide the 5 amps I need are switching.

Thanks for responding!

 

It may be possible to simply add a bit more filtering to the DC supply for the camera. BUT, also, the power leads from the supply to the camera must not share the same common conductor as the shield on the video cable bringing the picture back to the monitor.

Thanks for taking an interest.

This is what confuses me. Everything in a house shares a common ground. The shield and power supply therefor must share a common ground?

.

 

What sort of power supply is it? Plug-in "wall wart" type or "box" type with a power cord? Is there a ground conductor in the plug/cord and if there is, is it connected to mains ground when you use the isolation transformer?

Where the expectation is that an "earth" ground will be available for the input of a switcher, almost invariably "Y capacitors" are used. These connect each side of the power line to the earth ground terminal for EMI/RFI control purposes. They are limited by safety regulations to quite small values, since they pose a safety hazard if the earth ground goes open circuit. These may be involved in your issue.

Switchers also typically have a low-value capacitor between the secondary side and the primary side, again for EMI/RFI. This cap is also limited in max value and must be a special type to comply with safety regs. I would note that lots of Chinese manufacturers crank out power supplies that would fail most safety regulations.

Since the isolation transformer "fixes" the problem, it is very unlikely that anything related to filtering of the DC is actually an issue. If the iso transformer breaks the connection between the supply chassis and earth ground, making that connection externally will probably unfix the problem.

Many devices put small currents into the ground in an an AC distribution system - notably switchers as I described. Other than things with switchers, most things should not be putting current into ground, unless there is a failure. The problem with ground, especially at higher frequencies, is that voltage differences do occur due to currents flowing through resistance and inductance. When you are dealing with something like a video camera where the total signal amplitude is only about a volt and has high frequency components, it doesn't take much to mess things up.

 

Thanks for taking an interest.

This is what confuses me. Everything in a house shares a common ground. The shield and power supply therefor must share a common ground?

.

I am talking about the wires between the camera and the power supply, and also the cable between the camera and the monitor. THOSE are the grounds that should not be shared except at the power supply common terminal. The noise would be coming from the power supply current flowing through the video cable ground wire. THAT is what composes a ground loop.
The term "ground loop" is one of the more misunderstood parts of electrical and electronics. I hope that my explanation has helped.

 

Did the problem come on slowly or over night?

 

What sort of power supply is it? Plug-in "wall wart" type or "box" type with a power cord? Is there a ground conductor in the plug/cord and if there is, is it connected to mains ground when you use the isolation transformer?

Where the expectation is that an "earth" ground will be available for the input of a switcher, almost invariably "Y capacitors" are used. These connect each side of the power line to the earth ground terminal for EMI/RFI control purposes. They are limited by safety regulations to quite small values, since they pose a safety hazard if the earth ground goes open circuit. These may be involved in your issue.

Switchers also typically have a low-value capacitor between the secondary side and the primary side, again for EMI/RFI. This cap is also limited in max value and must be a special type to comply with safety regs. I would note that lots of Chinese manufacturers crank out power supplies that would fail most safety regulations.

Since the isolation transformer "fixes" the problem, it is very unlikely that anything related to filtering of the DC is actually an issue. If the iso transformer breaks the connection between the supply chassis and earth ground, making that connection externally will probably unfix the problem.

Many devices put small currents into the ground in an an AC distribution system - notably switchers as I described. Other than things with switchers, most things should not be putting current into ground, unless there is a failure. The problem with ground, especially at higher frequencies, is that voltage differences do occur due to currents flowing through resistance and inductance. When you are dealing with something like a video camera where the total signal amplitude is only about a volt and has high frequency components, it doesn't take much to mess things up.

It's a plugin wall wart. What do you mean by making the connection externally?

 

I am talking about the wires between the camera and the power supply, and also the cable between the camera and the monitor. THOSE are the grounds that should not be shared except at the power supply common terminal. The noise would be coming from the power supply current flowing through the video cable ground wire. THAT is what composes a ground loop.
The term "ground loop" is one of the more misunderstood parts of electrical and electronics. I hope that my explanation has helped.

The DVR and the cameras are connect to the house current by the same extension cord but the cameras are plugged into a 4 way pigtail from their own switching power supply while the DVR has a seperate switching power supply.

I still don't understand the ground loop concept sorry.

 

Did the problem come on slowly or over night?

I just bought the cameras and DVR. The ground loop interference isn't as bad as I have seen in pictures posted on the net by others having a similar problem. I'm assuming that it needs to be fixed for the sake of the cameras as much as picture quality.

Since the isolation transformer solved the problem I'm assuming A it would be easy to fix if I understood the cause and B I could just continue to use it if it doesn't waste a lot of watts, shorten the life of the cameras somehow, or pose some sort of safety hazard. The isolation transformer I assumed was fairly efficient because it weighs a ton but it is warm to the touch. One weird thing is that the switching power supply seems cooler plugged into the isolation transformer but that could be my imagination.

The isolation transformer has a three prong plug but the plates of the transformer core are exposed. Doesn't having exposed cores represent a safety hazard?

 

Does the wall-wart have a ground pin?

What I meant by making the connection externally was the assumption that the iso xfmr would disconnect the earth ground from the power supply, and to confirm that that was where the benefit was coming from the broken connection could be made directly in some fashion - a wire from the power supply's ground to earth ground. This would verify if the ground is truly the issue or something else is going on.

Just to be clear, please confirm or correct:

1. each camera has a two-wire power cable back to the DC output of a single power supply
2. each camera has a coaxial cable back to the DVR
3. the power and coax cables to each camera are routed physically close together and both are about the same length
   
4. the camera bodies are not grounded locally in any way (i.e. grounded ONLY by their power and signal cables)
   
5. when you use the isolation transformer both the DVR and camera supplies are run from the xfmr
6. the earth ground on the outlet is known to be good - straight back to the distribution panel which has a large ground wire to a ground rod or buried metal pipe

Does the problem effect all cameras?
If you disconnect all but one camera from both the power supply and DVR does the problem remain?

 

Does the power supplies have safety agency markings that look legitimate? Did you buy either of them from a vendor who shipped it straight from China?

 

Does the wall-wart have a ground pin? No, I have never owned one that does but I may look for one

What I meant by making the connection externally was the assumption that the iso xfmr would disconnect the earth ground from the power supply, and to confirm that that was where the benefit was coming from the broken connection could be made directly in some fashion - a wire from the power supply's ground to earth ground. This would verify if the ground is truly the issue or something else is going on.

Just to be clear, please confirm or correct:

1. each camera has a two-wire power cable back to the DC output of a single power supply Yes
2. each camera has a coaxial cable back to the DVR Yes
3. the power and coax cables to each camera are routed physically close together and both are about the same length The cables are siamese coax and power
   
4. the camera bodies are not grounded locally in any way (i.e. grounded ONLY by their power and signal cables) All the cameras are mounted to wood or plastic soffit
   
5. when you use the isolation transformer both the DVR and camera supplies are run from the xfmr I only attached the cameras switching power supply to the isolation transformer
6. the earth ground on the outlet is known to be good - straight back to the distribution panel which has a large ground wire to a ground rod or buried metal pipe I did the house wiring myself so I know it is done properly

Does the problem effect all cameras? Yes
If you disconnect all but one camera from both the power supply and DVR does the problem remain? Yes but one strange thing is the power indicator light on the switching powere supply stays on for about a minute after I unplug it.

 

Does the power supplies have safety agency markings that look legitimate? Did you buy either of them from a vendor who shipped it straight from China?

I got them from amazon but I'm sure they came from china, my guess is that the safety information can not be trusted.

 

To quote Bugs Bunny "Your hormones is fightin' with your capillaries."

One more experiment: Try connecting both power supplies to the output of the isolation transformer.

My suspicion here is that high frequency crud is what may be circulating in the loop, and not necessarily in the ground. When you put the iso transformer in place its "leakage inductance" (inductance formed by the windings that doesn't couple from the primary side to the secondary side - you can model it by putting a small inductor in series with the primary and/or secondary) is essentially blocks the high frequency component.

Do you have any power line filters kicking around - one of those tin cans with solder lugs on one end and an IEC power inlet on the other?

Do you have any of the big ferrite "beads" that are sometimes found on video cables or power cords? The "snap on" type would be OK.

The light on the switcher staying on is fairly typical with a light load. The input capacitor (i.e. the filter cap after the bridge rectifier) stores enough energy to keep the switcher going briefly.

Some of the supplies I've seen from China have fraudulent safety markings. Some are very good supplies with genuine approvals. If it came from an Amazon "marketplace" vendor, even if shipped by Amazon it may be dubious. If it was sold by Amazon it has a better chance of being OK, from what I've seen. Electrical safety agencies don't care if RFI from your power supply makes airplanes fall from the sky. Agencies like the FCC don't care if your power supply burns your house down.

Can you open the case on your camera power supply without damaging it? If you can, can you post a pic of its innards? Same question for the DVR supply. I'm assuming you don't have any other supplies on hand to try.

 

To quote Bugs Bunny "Your hormones is fightin' with your capillaries."

One more experiment: Try connecting both power supplies to the output of the isolation transformer. Can't it only has one plug

My suspicion here is that high frequency crud is what may be circulating in the loop, and not necessarily in the ground. When you put the iso transformer in place its "leakage inductance" (inductance formed by the windings that doesn't couple from the primary side to the secondary side - you can model it by putting a small inductor in series with the primary and/or secondary) is essentially blocks the high frequency component. I have forgotten almost everything I was taught about circuits over the last 35 years but I could probably Identify a small inductor. It will take me awhile to find something I can tear apart to get it out of. Is that a permanent solution?

Do you have any power line filters kicking around - one of those tin cans with solder lugs on one end and an IEC power inlet on the other? No idea what you are talking about

Do you have any of the big ferrite "beads" that are sometimes found on video cables or power cords? The "snap on" type would be OK. No but I have a lot of hardware like nuts and bolts?

The light on the switcher staying on is fairly typical with a light load. The input capacitor (i.e. the filter cap after the bridge rectifier) stores enough energy to keep the switcher going briefly. Thanks for explaining that

Some of the supplies I've seen from China have fraudulent safety markings. Some are very good supplies with genuine approvals. If it came from an Amazon "marketplace" vendor, even if shipped by Amazon it may be dubious. If it was sold by Amazon it has a better chance of being OK, from what I've seen. Electrical safety agencies don't care if RFI from your power supply makes airplanes fall from the sky. Agencies like the FCC don't care if your power supply burns your house down.

Can you open the case on your camera power supply without damaging it? If you can, can you post a pic of its innards? Same question for the DVR supply. I'm assuming you don't have any other supplies on hand to try. All the supplies I have on hand are less than what one camera calls for

I have a whole collection of wall warts I have collected over the years, maybe two dozen. Most of them are the transformer type not the switching power supply kind. I hooked up one to one of the camera and no flicker but the biggest one I had was 300ma I'm just a little worried about underpowering a camera. Searching for transformers on the internet I'm finding that the ones that are not switching never go above one amp. I did find this one that has three prongs but not sure why that would matter. https://www.ebay.com/itm/4-CH-Camer...hash=item3369869480:m:mE6Ne-y92MEEuywSG2cKatA