For a couple years now, I have been replacing DVR cards in a PC from lightning hits. The cameras are outside grounded in the open area on the building and I have lightning rods install by a professional. I have a large antenna on the property next door that is probably bring all the lightning to me to make things worse.

It seems it is hitting the cameras (last thing that is recorded is a bright flash on one of the cameras) and the EM spike travels through the coax to the DVR card (PC and its power supply never been replaced AND 12 volt DC PS to the cameras never a problem). And lost one camera with 5 DVR cards fried.

I bought a $600 16 port protection device (BNC to BNC). I was told it would solve this and it is grounded as instructed. This does not work either.

I noticed the ports on the DVR card that are BNC to cat 5 via transformers and back to BNC at the DVR seem to survive, but looking at a resonable cost fiber solution. As I think eventually the right hit will spike the cat 5 cable if I go cat 5.

Anyone have experience in this area?

I think the DVR card is a little weak in design and thought if I go to fiber (2 feet of it just before the DVR with a BNC-BNC coupler) it would just be a bright flash light in the fiber and no ground involved. Hoping that will solve the problem.

I found Blackbox has a $2000+ US pair (RX/TX) version. I would need 16 of them so at $400 DVR card, that's out.

 

You really should be able to build/find a surge arrestor that works for your application, seems weird the one you bought doesn't work, are you sure it's grounded properly? Can you provide any docks on the unit you purchased?

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It is a passive device. When I looked at the old one it looked like high speed diodes in it. So I went to another company that said theirs are the best (imagine that). And bought theirs. Still dead DVR cards.

Only connection (other than the BNC patch cable and camera BNC cables) is a ground and we've had the electrician out to check that as well. Only the DVR card dies in the hits, nothing else. It is weird.

 

I'd be looking for new DVR cards.

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These Geovision cards have the best software and it is only in one location I have the problem. I put an old digivue in for now.

I think I will try to find a low cost CCTV to fiber TX/RX pair. Not sure how much work it would be to run them through opto isolators and I would still have to have a ground, but I am told by the electricians it is not the gound.

 

We used to have that problem, we solved it by going to fiber optic cable to each camera.

edit: here's one that I use in my class:
http://www.supercircuits.com/search_...=fiber%20optic
It's $500, but I haven't found a cheaper one yet.
Since you only have the problem in one location something like this will probably be your best bet. We had 5 cameras on our building (outdoors) and it was pot luck which one would cause a problem. The building is 1 million square feet, so the lead in cables were quite long.

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gerty

 

Gerty,

Thanks for the link. I used to buy from them all the time. I found a local place that has them for $330 a set. So if the boss give the OK I am going fiber.

 

$330 !! where is that? I could use another set. Sometimes I have to go to other schools and give lectures on fiber and I like to bring "stuff" for show and tell..

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gerty

 

Why are the cameras grounded? That's dumb. When there is lightning activity, the ground potentials change and there will be huge currents flowing down your wires. The lightning doesn't have to strike your camera or strike at all, merely the potential gradient over the ground between the wires can destroy your devices.

If the camera was electrically isolated from the DVR, then you could ground it; I would only do it for noise reasons (which are likely not existant) and not for lightning immunity. So I wouldn't ground them.

Oh, boo. Not everything can be blamed on the neighbours, annoying as they may be. Anyway, that's something you can't change.

Unlikely the lightning is specifically picking out your cameras unless they're on big poles.

Isolation is the normal way to protect from ground pot. shift.

As an example, I know a fellow that had to provide alternate RS422/485 communications between highway signage as the interfaces kept failing in bad weather. He replaced the interfaces with isolated versions (<3kV) and the devices hadn't failed since.

As another example, airport aerodromes, afaik, use underground grounding mesh/cable to reduce the ground impedance and therefore potential difference.


Have a look for 75ohm (or 50ohm, whatever you are using) isolation transformers. Or use back-to-back 75-300 <==> 300-75ohm adapters. Or make your own. Depends on cost, I guess. Some examples:
Antenna signal galvanic isolation
http://www.servinternkft.hu/sites/se.../TC8235GIT.pdf

You want to increase your isolation voltage rating to as high as possible.

Fibre has the best isolation, but is expensive.

 

Is fiber really that expensive? TOS link fiber for audio goes over plastic fiber. Video is higher frequency but that's mostly about finding xmitters/receivers than the fiber itself, true glass fiber is expensive but for runs of only a few hundred feet is it required?

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Dougy83,

I have tried isolation transformers and high speed diode protection (two models). $600US for the last one. Also with and without grounds and off.

The first post did say grounded as instructed. That means I put the grounds on.

Going with the fiber. As this is the only way I see solving this.

Oh Boo? I will leave that one alone. Just pointing out what is around the problem location.

 

The runs on quite a few are 300-500 feet. But I will just make small patch runs 2-3 feet to isolate them at the DVR. So that might work if they handle NTSC video.

Will look at TOS and plastic. Thanks for the info.

 

TOSC is an audio standard though they're not gonna work for video directly, I don't know what kind of LED's and receivers you would need for high frequency applications.

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I found a local source, but they were not cheap. Waiting on another place to call me back. The are talking $69 each end.

 

Stupid markups. You can buy toslink modules from digikey for 20 bucks either end, mind you you have to put the boards together that use them. Not gonna help you anyways I looked into it a little more it's digital only. PS it's not TOSC it's Toslink I misremembered the name.

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