CCTV DC adapters blown + Ground loop Problem

Calibos

Hiya lads,

I am trying to get my fathers CCTV DVR + 3 Camera system working again. Comapany that installed it went bust and another company phoned to come out and repair were a no show.

12v DC 500mA adapters are dead.
Cameras are Panasonics and the voltage label reads 12v 270mA

There were 3 cameras with 2 cameras connected in series, (cable going from power socket on one to the other camera and from the same connector then a single run of cable to a 12v 500mA DC adapter) Third camera had its own DC adapter of the same spec. Cable runs were 3 core mains cable due to the length of the runs I presume, wired to the dc adapters with their power tips cut off with insulation tape.

IIRC, the same two cameras that were powered from the same adapter always developed rolling black lines that got worse over time till the cameras blackout out which I presume was the dc adapter dying. Company that installed the system replaced the adapters once which cured the problem but it happened again a few months later by which time the company had gone bust. The system has been lying idle for over a year now.

So I am not sure whether the rolling lines are a ground loop or just a symptom of the overloaded dc adapter. The fact that it was always the 2 cameras powered from the same dc adapter that developed the rolling lines make me think it was down to the adapters.

I presume I should buy 3 new dc adapters, one for each camera. What mA rating dc adapters should I get though?

Michael Collins

Yeh it sounds likes it's the power supplies alright. Apart from anything else:

270 mA + 270 mA = 540 mA > 500 mA

so it's not hard to see why that company went bust. Bit of a fire hazard too.

Chances are the rectifiction or regulation stage has failed inside the power supplies, possibly letting 50 Hz noise from the mains through, which could cause the lines you are seeing.

Yep, replace the power supplies with three individual ones if possible, rated at least 500 mA each I'd say, just to be on the safe side

Calibos

Do these look ok mate?

http://www.maplin.co.uk/Module.aspx?ModuleNo=32746

Just a quick question.

The original adapters had their power tips cut off with the 3core mains cable twisted together with the much thinner dc adapter cable and held together with insulation tape.

Should I do the same, ie cut the power tips of these new ones except join the wires together with some of those little plastic connection block thingies obviously?

fishdog

What I did was used a HKC power supply unit. It costs about €50 and contains a 12 volt battery. It is abot the size of an alarm panel and looks a bit like one as well. It will easily have the capacity to supply 3 cameras and will also power the cameras in the event of a power cut. I guess you may not want that, but it will do it anyway! I the last one I installed can supply over 1 amp at 12 volts.

Simple, cheap and effective

Michael Collins

Yeh that looks fine. There's a fixed voltage adaptor available for 12 V at 400 mA - in theory this should do it the job too, but maybe the 500 mA would be the safer option considering this is the spec of the original PSUs.

Yes at the very least use the terminal blocks instead of twisting the wires together. If you'd like a bit of flexibility you could always buy these for the cables that connect to the power supply unit. You'd have to solder them onto the wires though. But there's no problem cutting the cable as you say and using some connectors.

Perhaps consider Fishdog's suggestion too, so you could just have one run from the PSU, looped along to each camera...whatever is handiest.

Calibos

Thats a great idea. I don't actually have a soldering iron atm but that just reminded me that I planned to get one for a few other little jobs.

So thats a 40mm fan for the DVR, 3x 500mA dc adapters, 3 powertip sockets and a soldering iron from maplins so!

Thanks again lads.

fred funk }{

fishdog wrote: »

What I did was used a HKC power supply unit. It costs about €50 and contains a 12 volt battery. It is abot the size of an alarm panel and looks a bit like one as well. It will easily have the capacity to supply 3 cameras and will also power the cameras in the event of a power cut. I guess you may not want that, but it will do it anyway! I the last one I installed can supply over 1 amp at 12 volts.

Simple, cheap and effective

I wouldn't use the battery as back up, a UPS would be a better job. You will need a UPS for the DVR anyway. No point having the cameras working when the DVR isn't.

fishdog

fred funk }{

I wouldn't use the battery as back up, a UPS would be a better job.

The cameras use dc. A UPS system gets dc from batteries and then uses an inverter to change it to AC. The problem is AC is not compatible with the cameras. According to the OP the originally the cameras were supplied by:

12v DC 500mA adapters

I have used a single power supply unit several times for multiple cameras and it always worked. It gives a perfect dc output, nice and flat! It is handy that extra cameras can be added if required without needing more power supplies. This method is very popular due to the fact that it is so simple and cost effective.

I admit "stole" the idea from cctv guys!!

A UPS is ideal for the DVR alright.

fred funk }{

The cameras use dc. A UPS system gets dc from batteries and then uses an inverter to change it to AC. The problem is AC is not compatible with the cameras. According to the OP the originally the cameras were supplied by

I know that, why can't you power the transformers from the UPS?

I agree with you about the PSU, those individual one's will only torment you. They're unstable and messy to change when the blow (which is often). The PSU's that come in a large steal box are ideal, I use them all the time. You can get them in various sizes and very rarely give trouble.

Stoner

fred funk }{ wrote: »

why can't you power the transformers from the UPS?

that's what I did in my place, just broke the 220Vac CCTV circuit through a UPS, worked fine, the DVR is on the main UPS, no issues 5 years later.

Calibos

I ordered the stuff from Maplins. The were out of the 500mA dc adapters so I ordered 3 400mA instead. The cameras are 270mA remember so 400mA means they are still over specced for the cameras anyway.

I understand the installers used mains cable for the camera runs to the adapters due to the length of the runs. ie a thicker cable than the very thin 12v dc adapter cable is required for these length runs. However the used quite thick 3 core mains cable which doesn't bend around the corners very well and pops the conduit. Looks very messy. Could I get away with replacing these runs with thinner 2 core mains cable, (ie the gauge of cable for a dvd player for example) Would mean I could really tidy up the cable runs while I am at it.

On other thing I forgot to mention in my first post. Remember I explained how one camera had its own run of cable to its own dc adapter whereas the other 2 cameras were daisychained on another run and shared the second adapter. (I am now giving each camera its own run and its own adapter). Well I forgot to mention that both of the adapters where wired to the same plug. Is this something I should or could do. ie wire the 230VAC side of the 3 adapters to the same 3 prong fused plug? Would simplify the wiring and save me having to add another 4 gang adapter.

DublinDilbert

Calibos wrote: »

I ordered the stuff from Maplins. The were out of the 500mA dc adapters so I ordered 3 400mA instead. The cameras are 270mA remember so 400mA means they are still over specced for the cameras anyway.

I understand the installers used mains cable for the camera runs to the adapters due to the length of the runs. ie a thicker cable than the very thin 12v dc adapter cable is required for these length runs. However the used quite thick 3 core mains cable which doesn't bend around the corners very well and pops the conduit. Looks very messy. Could I get away with replacing these runs with thinner 2 core mains cable, (ie the gauge of cable for a dvd player for example) Would mean I could really tidy up the cable runs while I am at it.

On other thing I forgot to mention in my first post. Remember I explained how one camera had its own run of cable to its own dc adapter whereas the other 2 cameras were daisychained on another run and shared the second adapter. (I am now giving each camera its own run and its own adapter). Well I forgot to mention that both of the adapters where wired to the same plug. Is this something I should or could do. ie wire the 230VAC side of the 3 adapters to the same 3 prong fused plug? Would simplify the wiring and save me having to add another 4 gang adapter.

Mains cable for the 12V supply to the cameras, what were they thinking!!! Get a roll of 2 core bell wire from an electrical wholesaler, have never bought it, but it would be very cheap.

Yea would make sense to run 3 lots of bell wire out one to each of the cameras.

Get a plug board for the 3 adapters to plug into...

fred funk }{

I have often used mains cable for running low voltage, normally .5 or .75 flex. Very little drop off over longer distances.
Ideally you should try sourcing 250AC locally and put the transformers in an outside IP rated box. You wont have any problems with DC drop off.

Check to see if the cameras can take 24VAC because that would be a lot more stable and cause you less hassle in the future.

fishdog

why can't you power the transformers from the UPS?

1) Your UPS system will not last as long. Why waste its power on cameras?? Unless it is a very large UPS system it will not last for too long anyway. They are expensive units relitive to a 12 volt power supply unit.

2) UPS is powered by AC changes this to DC then back to AC . If the adapters were added to this it would be changed back to DC again. Each transition from AC to DC or DC to AC will cause a loss. This system will result in lots of losses!

3) The transformers for the cameras may not work as well with a UPS input. This is because UPS outputs are closer to a square wave than a sine wave. This would not be the case in high end UPS systems, but then you are into serious money. The transformers are not designed to work with an input that is not pretty close to a perfect sine wave. This can also lead to problems with harmonics. The result is the transformers may overheat, have poor voltage regulation. This might not be too good for your cameras!

The last time I bought cameras from Borsatec they recommended using a single 12v power supply unit.

I have often used mains cable for running low voltage, normally .5 or .75 flex. Very little drop off over longer distances.

The volt drop for a cable is expressed as mV/A/m. This means that if the current is low, (in this case very low at 0.27A) the volt drop will be very low even for a long run on a thin cable.

Ideally you should try sourcing 250AC locally and put the transformers in an outside IP rated box.

250 typo?? Its 230 volts AC. I don’t agree. It looks terrible!! A transformer is then required for every camera. With a 12 volt supply your camera can be much more discreet and a lot of safety wiring regulations need not apply. Also when servicing/repairing/replacing the cameras outside at the top of a ladder work can be done much more safely by people that are not qualified electricians. Only qualified electricians are permitted to connect mains voltage to transformers.

I have to admit that I was talking to an expert about this today and he told me that it would be possible to use the UPS in the way described, but careful examination of the data sheets for both the UPS system and the transformers would be important. So
fred funk }{ is correct it could be done that way. I guess it is down to personal choice!!

Calibos

Just thought I would update this thread.

The Maplins stuff came today.

Installed the new 40mm fan in the DVR, Ran 3 new runs of 2 core flex, soldered the connection tips to the cables, plugged in the 400mA adapters.

Jobs a goodin'. All cameras working with no rolling black lines on the display. Lets hope it stays that way.

fishdog

Jobs a goodin'

Fair play!!
There is always a certain amount of satisfaction when you fix something yourself.