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Designing a snubber

Discussion in 'Electronic Design' started by stefanv, Dec 21, 2005.

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  1. stefanv

    stefanv Guest

    specs for a 4000 watt 60hz snubber?

    When the power goes off, I have an in-line inverter system (Trace 2500) t
    provide AC to my house. The power lines in my area being above ground
    lightning sometimes hits the poles and gives huge spikes and surges
    Doesn’t happen often, but when it does the next morning people complai
    about there TV’s and computer’s blowing up and so on.
    I decided to put a home-brew 4000 watt spike protector before the inverte
    to protect whatever is on it. I was thinking some heavy-duty 150V varistor
    accros neutral-hot-ground, and a snubber.
    About the snubber; looking at some resources, I’m still confused. In m
    case, AC power should it be:
    - L in series with the hot line, C after that across hot and neutral?
    - To slow down the spikes at 60Hz, what should the values be?
    - Will this handle 4000 watts?
    - Any suggestions on winding my own L (core, turns, wire size)?

    Help is appreciated!

    Stefan V
     
  2. Robert Baer

    Robert Baer Guest

    Even a cat cannot snub *that* well.

    Getting a bit more serious, use a number of lossy ferrite toroids, 3
    or 4 in series (glue together to make "fat" toroid) one turn on the hot
    side, then a 5-10 turn per line common mode xfmr using same lossy toroid
    material; put before anything else.
    MOV varistors may be good for fast stuff, but degrade over use - just
    like tissue degrades with exposure to radiation.
    So they can turn to crap in a short while with a goodly storm.
    Use carbide ones - they never degrade.
    With something that nasty, i cannot help much.
     
  3. stefanv

    stefanv Guest

    Thanks for the advice. Not knowing to much about this matter, you wouldn'
    put a capacitor at all? Just the toroid in series with the hot? (and som
    carbide MOVs after)

    Stefan V
     
  4. Robert Baer

    Robert Baer Guest

    A capacitor might help, but with the possibility of rather nasty
    spikes, the capacitor would have to be rated to at least 2KV.
    The series lossy inductor i think would be best done as one in series
    with high side and one in sereis with the low side.
    That first tends to phase shift the current WRT voltage as well as
    attenuate spikes; next the common mode choke then helps to block (common
    mode) spikes.
    Get the highest voltage rating common mode choke possible, for 440V
    lines or higher...so arcing from one side to the other cannot happen
    and compromise the choke.
    At that point, a good varistor would seem to be the next step,
    followed by another lossy inductor pair (one in series with high side
    and one in sereis with the low side), then another common mode choke and
    *then* maybe a capacitor (600V or better).
    In fact, one could use a spark gap voltage limiter at the start and
    across the varistor.
    The first one at the front should have the highest current rating
    that you can afford (or make it relatively easy to replace and have a
    number of them available for replacement after the *big zap*).

    Mind you, a lot of what i am "recommending" is guesswork, but i know
    that the series inductor pair and common mode choke does work wonders -
    from experience.
    The use of carbide varistors and spark gap limiters are from from others.

    You may need to do a little experimenting, and if game, make a tester
    that creates big zaps!
     
  5. Ian Stirling

    Ian Stirling Guest

    4Kw isolation transformer, with a moderate sized low ESR cap on the output?
     
  6. JosephKK

    JosephKK Guest

    An actual lightening strike to the mains will likely explode the transformer
    and damage all downstream electronics. More to the point would be
    lightening / surge protection at the mains entrance, and again before any
    [relatively] sensitive load {like you wish to protect with your
    transformer}.
     
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