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Christmas lights

Discussion in 'Electronic Repair' started by klem kedidelhopper, Dec 18, 2012.

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  1. I've been reading the other thread about Quartz halogen lamps and have
    found it very interesting. However since this is a bit off that track
    I've started this new thread.

    I seems like in the last few years it has become impossible to buy
    small Christmas light series strings that have conventional lamps in
    them. IE: When a filament goes out they all go out. I've noticed that
    "something" happens to these new lamps that effectively makes them a
    dead short when the filament opens. This then maintains the continuity
    of the string and keeps the other lamps lit. But of course this comes
    with a high price. A higher voltage is placed across each of the
    remaining good lamps when this happens.

    Little by little as they over cook, and each filament reaches the
    premature end of it's life and opens, that lamp is essentially
    replaced by another dead short, thereby running the remaining good
    filaments at even a higher voltage. Naturally catastrophic failure of
    all the rest of the string is inevitable and systematically occurs
    unless this "shorting" action fails on a particular lamp and it
    actually "opens". Then the remaining lamps are spared.

    I know this is what's happening because I've tried to repair several
    strings like this. Last night I looked at two identical 50 lamp
    strings. One had about six lamps out with one open. There were 35
    lamps out on the other, all with with shorts across them except for
    one that was "open". The remaining lamps were still good.

    My wife seems to think that not having all the lights go out when one
    filament opens represents convenience, and trying to explain series
    circuit theory to her is an exercise in futility. So anyhow I now have
    one string which I've added 8 additional lamps to for a total of 58
    2.4 V lamps on it. It runs a bit dimmer but it should last a lot
    longer. I also now have a few spare lamps as well.

    As much as it pisses me off you have to give the Chinese credit for
    figuring out a way to sell more Christmas lights under the guise of

    Does anyone know what is actually happening in these lamps to turn an
    open filament into a dead short and begin this "runaway" effect? Lenny
  2. As we say here in America you literally got "knocked on your ass".
    It's amazing considering some of the stunts we've all probably tried
    in the interest of them being a learning experience that we're still

    I remember when I was a teenager grabbing an old tube type TV chassis
    off the bench on a hot Summer day. I caught 450VDC from one arm to the
    other. I think that the only thing that saved me and my heart was
    possibly the skin effect of my soaking wet sweaty Tee shirt. Lenny
  3. John-Del

    John-Del Guest

    If you notice them... These miniature lamps are usually wrapped around trees or otherwise stuffed into decorative foliage, and single lamp failures often go unnoticed unless you're specifically looking for them.. Lenny's idea of adding lamps in series is a good idea. Years ago, I had an X10 setup for holiday lighting, and would run the dimmer modules for the light strings. Just dropping the brightness a bit kept them running almost forever.

    My son just bought a set of similar lights that use LEDs. We'll see how long these last.
  4. I took a good look at these lamps tonight under a magnifier, I
    noticed a very curious thing. At the base of each lamp the thin wires
    go through the bulb and attach to the posts that the filaments are
    then welded to; If you look into the bulb, at the base of these posts,
    inside each lamp there seems to be a thin wire wrapped around the
    posts that one would think would short them out. It obviously doesn't
    happen right away but after a period of time, (heating), it does seem
    to. Perhaps that is it's purpose, to burn through an insulating layer
    on the posts after a brief time and destroy the lamp. And one further
    observation. In looking at the filaments on all the "shorted" Kamakazi
    lamps It appears that the filaments never opened, rather the shorting
    wire must have finally burned through the posts and shorted the lamp
    What an insidious clever way to sell more Christmas lights. Isn't it
    fascinating the lengths that some people will go to to separate us
    from our money? Merry Christmas! Lenny
  5. Or, keep the remaining series string going even after the lamp burns out.

    Mark Z.
  6. Thank you Gareth. I did miss that link. So it seems that my theory
    about the short,(shunt) was pretty much right on the money, except for
    one thing that is. The article mentions, as I had suspected that when
    the filament opens, current then flows through the shunt. This heats
    the shunt, thereby causing it to melt it's way into the posts and thus
    providing continuity to the series string. Although that does sound
    ingenious, as I had mentioned in my last post, upon examining each
    "shorted" lamp under high power magnification it appears that in
    almost every case all the filaments appear to be intact. That would
    suggest that this melting and subsequent shorting of the lamp occurred
    before the filament opened. Naturally I couldn't measure these
    filaments with the short across them to confirm this, but they do look
    to be mechanically sound. So I guess what it comes down to is I think
    that we're being screwed with these Christmas lights. As an
    interesting side note. I have considered using some of the surviving
    lamps in parallel as low voltage "street lights" and to illuminate
    model buildings on my Lionel train layout. I'll be sure to fuse the
    circuit if I do.... Lenny

  7. And *really* crap quality LED's that have a shorter run life than the lamps

    I have had more than one cheap LED flashlight where up to 4 out of 9 LED's
    quit rather quickly, even had one even strobing at a visible rate.

    Bought a higher quality flashlight. About three years old now, use it daily,
    still OK.

    Mark Z.
  8. hr(bob)

    hr(bob) Guest

    I always add a couple of extra sockets and lamps to every string of
    lights I own, both outsie and inside. That slows the failure rate WAY
    down. Then, at the end of the season,I check all the strings of
    lights before I put them away. THe runawa effect I have seen, it can
    be quite spectacular if you are there at the right time. Eventually,
    as the number of remaining working lights quickly reduces, eventually
    the current gets so high that one of the shunts fails. The shunts are
    actually regular wire, but with insulation that breaks down at may 50
    volts. When a bulb burns out, the voltage across the open bulb rises
    to the supply voltage, 120 or 240, the insulation breaks down, and the
    shunt completes the circuit, lighting up the remaining bulbs.

    I also have a device from 30+ years ago that starts out high
    resistance and quickl, 2 -3 seconds, goes down to less than 1 ohm.
    This is in the supply for the lights. This prevents the high initial
    surge that occurs because the filaments are cold, and pretty much
    eliminates the initial flash / failure that we are all familiar with.
  9. But no one has addressed the fact that these filaments I've observed
    under magnification on the bad lamps that I have pulled from this
    string do not seem to have opened. However the lamps indeed read dead
    shorted though. So just as I've suspected from the beginning the shunt
    must be burning it's way through the posts and rendering the lamp
    useless in spite of the lamp still having a good filament. Lenny
  10. I think that going forward, (from this point anyway) the answer is
    that the filaments on these crappy bulbs are probably over rated, and
    therefore full line voltage should probably not be applied to the
    string. I'm going to buy a bunch of identical new Christmas light
    strings of the same type, (on discount, after Christmas of course).
    This way they will be cheap enough so that l can buy enough to be able
    to cut and past extra lamps onto each string. This will essentially be
    equivalent to running each string at something like 105 to 110 volts,
    and this should increase the life span of the lamps substantially. In
    addition I am also going to speculate that since the lamps will then
    be running cooler it may keep the shunts from burning through the
    posts and rendering lamps with otherwise good filaments bad as well.
    This tactic may not stimulate the economy but it should keep the
    Christmas light money in my pocket rather than theirs. Merry
    Christmas! Lenny
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