Lightning Strikes

Discussion in 'The Projects Forum' started by vin2install, Feb 1, 2008.

  1. vin2install

    Thread Starter New Member

    Feb 1, 2008
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    I need help on project. I am trying to prevent lightning strikes from frying 12vdc cameras. Everytime that the voltage hits 18 volts or higher than the CCD module starts frying.

    Would it work if I put a TVS diode in line with the camera?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Are you using these cameras to film lightning strikes?

    hgmjr
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    No.

    About the only way you can absolutely assure protection against lightning is to seal the camera in a solid stainless steel enclosure, and bury it under 100 feet of saltwater bog.

    Low-voltage MOVs (metal oxide varistors) will help a great deal, in conjunction with TVS diodes and caps to absorb the intial voltage rise until the diodes and MOVs can begin conducting.

    There's not much one can do to protect against a direct strike by lightning; it's path is unpredictable. Lightning rods would help a great deal, but they're not an iron-clad guarantee.
     
  4. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    You can also throw in some gas discharge tubes and spark gaps in addition to the MOVs TVSes, series resistive elements and MOVs. But as Sgt Wookie pointed out... there isn't much you can do for a direct (or even nearby) strike.
     
  5. vin2install

    Thread Starter New Member

    Feb 1, 2008
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    I didn't mean the camera getting struck directly by lightning. I meant the voltage surge caused by lightning. I repair security cameras. So the most common fault of these sensitive 12vdc ccd modules is that if there is a surge that spikes the voltage for a split second than the ccd modules capacitors start popping off. So i'm trying to come up with a cost effective way to kinda integrate a self resetting fuse of some sort that would cut the line at a certain voltage and then reset itself afterwards. But the whole setup has to be small enough to fit in the camera housing.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Strikes caused by lightning are problematic to the extreme. We're talking millions of volts, and the current is nothing to sneeze at either. When they hit a power or TV cable line, repercussions are felt for miles.

    I didn't mention good old-fashioned spark gaps. Those are generally hermetically sealed in a glass enclosure, and can take a few indirect strikes. The voltage has to build up pretty high to jump the gap, but if the electrodes are sharply pointed, much can be bled off before it builds up too high. Once the spark jumps, the electrode points are blunted, resulting in a higher voltage needed next time to bridge the gap.

    MOVs are great, but slow-acting. They will fail like anything else if they get too much current through them. They also act like rather large capacitors, which will dampen video signals enormously, causing impedance mismatches if not properly selected, or damaged after a near-strike.

    Perhaps MOVs and TVS diodes together would be your best bet. The MOVs have enough capacitance to "suck up" some of the faster-rising transients, allowing the TVS diodes time to conduct. However, you would have to protect the power supply, the video output, and any control circuits (if applicable).

    The power supply and control circuits would be a relative snap, but you would have to ensure that the video line was 75 Ohm impedance all the way; otherwise you would have a great deal of signal degradation.

    Even if things were perfectly matched from the factory, a single lightning strike could mangle those components, and make troubleshooting more problematic than it is already.

    I appreciate what you're trying to do. I wish I could give you better answers.
     
  7. rwmoekoe

    Active Member

    Mar 1, 2007
    172
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    vin,
    just low-pass-filter your power supply to the ccd with say, (how much current do you need for the ccd?) 100ohm res (or a small inductor) in series and 100uF cap to the ground. parallel the cap with a 15v 1watt zener.
    good luck!
     
  8. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    Power -> large filter network using coils and caps with arc suppressors -> varistor -> transorbs-> camera. You can build this as a custom surge suppressor for them.

    You also want the signal line protected but that depends on the signal.
     
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