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Thread: christmas tree light schematic diagram?

  1. #1
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    christmas tree light schematic diagram?

    I have a set of lights that the first (closest to the plug) half works, the second half is dark. Fuses are ok, I replaced several of the bulbs. There are three wires along the length of the string (not going to each light)- are the bulbs series?, parallel? a combination?

  2. #2
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    I'm pretty sure it's two sets in series.

  3. #3
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    quote:Originally posted by mycatisretarded

    I have a set of lights that the first (closest to the plug) half works, the second half is dark. Fuses are ok, I replaced several of the bulbs. There are three wires along the length of the string (not going to each light)- are the bulbs series?, parallel? a combination?
    I know a bit about Christmas lights (you can check out our display's website at http://www.plymouthlights.com)

    The strings are wired as two sets of 50 bulbs in a series. The two series are in turn wired in parallel.

    What this means is that if one bulb is loose, missing, or defective, half the string will go out, as you have already noted.

    Your options are:

    1) Toss the string. They're usually less than $2 to replace. If you do this, first pull the bulbs out to use as future replacements in another string.

    2) Buy a cheap light tester from Target or the like. They cost about $5, and once you learn to use them (they're a bit finicky) they work very well. What they do is sense voltage and will find the bulb that isn't continuing the series. You can then replace this bulb, or tighten it up in the socket, and all will be well.

    3) Do the "old fashioned way" and remove each bulb, put it in the known-good half of the string, see if it lights that half up, repeat ad nauseum, until you find the bad bulb. This takes forever, and in my experience you stand to screw more bulbs up that way than correct the problem.

    My recommendation would be #2, unless you just want to toss the string away as in #1.

    Good Luck!

    -Tim

    P.S. See http://www.howstuffworks.com/christmas-lights.htm for an excellent description on how these strings are wired up.

  4. #4
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    yup 2 sets of series, 50 in each, you may want to just toss that strand and get another, a new strand costs less than any of those testing tools and you may have a short in it somewhere that is keeping the other half dark.

    I routinely toss defective strands whilst I string 4800 lights on my trees and house, Next years goal is 10,000

    Now the question for the electricians is this,

    How many circuits should I run to power this Clark Griswald Holiday Spectacular...

    Dan in PROC
    It's Like I've always said, it's amazing what an agnostic can't do if he dosent know whether he believes in anything or not

    Monty Python's Flying Circus

    Dan in Harrisburg, NC

  5. #5
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    I usually diagram a set of christmas lights by boiling a pot of spaghetti and throwing it against the wall. But in your case, a simpler solution is possible.

    It sounds like you have a 100-light string. This is two 50-light strings in parallel, and within each string the bulbs are in series. Each bulb is rated at 2.5 volts, and when the bulbs are in series 50 of them give a total rating of 125 volts.

    The drawback of serial bulbs is that if one is missing the whole string goes dark. Most modern lights have bulbs that short out when the filament burns out, which keeps the strand alive. However, when one bulb shorts out the voltage to the other bulbs rises, which shortens their lives. The most common failure mode of these types of strands is that several bulbs fail, which raises the voltage to each bulb enough so that either they all fail, or one burns out completely. At this point, replacing bulbs one at a time does no good; new bulbs just get fried immediately by the over-voltage.

    Since these strands typically cost between one and five dollars, the most sensible thing to do is to replace the entire strand. To forestall replacement, it makes sense to repair burned-out bulbs as soon as possible.

    Nick

  6. #6
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    quote:Originally posted by pierhogunn


    I routinely toss defective strands whilst I string 4800 lights on my trees and house, Next years goal is 10,000

    Now the question for the electricians is this,

    How many circuits should I run to power this Clark Griswald Holiday Spectacular...
    You can run quite a few mini's on a standard 15 or 20-amp circuit. There are two varieties of mini's these days: Energy Saving and Super Bright. Target, Wal-Mart, and some others sell the Energy-saving and they are about .2A/100. Menards and a few others sell the older Super Brights and they are about .33A/100.

    So if you wanted to power 10,000 super brights (worst case) you're talking about 33 amps, or 2 dedicated 20A circuits. If you're talking C9's, you're gonna pull MUCH more power as those babies are 7 watts a piece.

    By the way, if you want to visit the "BT3Central" of Christmas lighting, point your browser to http://www.planetchristmas.com/chatroomhorizontal.htm . I'm a regular there and these sorts of questions come up all the time. (EDIT: As Murphy would have it, the site appears to be down right now. It's a great site, so check back later if you're interested in Christmas lighting at all)

    -Tim

  7. #7
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    Well, since the Christmas light specialists are checking in, can I seek some advice?

    I make a 5 pointed star for the arch over the front doorway. The arch radius is about 5'. Up to now I've used a mini-light multi-stand string, with a different color on each strand. There's controller offering several blinking patterns. It's real hassle to troubleshoot, partly because I've got each strand going in a different direction.

    How would you create a 5' star? What kind of lights would you use? How would you form the star?

    I've thought about using those flexible tubes from the HD lighting section (you know, the kind used for accent lighting on bookshelves or display cases.). Would that work?

    TIA

    JR

  8. #8
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    quote:Originally posted by Nick Keenan

    ...
    The drawback of serial bulbs is that if one is missing the whole string goes dark. Most modern lights have bulbs that short out when the filament burns out, which keeps the strand alive. However, when one bulb shorts out the voltage to the other bulbs rises, which shortens their lives. The most common failure mode of these types of strands is that several bulbs fail, which raises the voltage to each bulb enough so that either they all fail, or one burns out completely. At this point, replacing bulbs one at a time does no good; new bulbs just get fried immediately by the over-voltage.

    Since these strands typically cost between one and five dollars, the most sensible thing to do is to replace the entire strand. To forestall replacement, it makes sense to repair burned-out bulbs as soon as possible.

    Nick
    The engineer in me somehow makes me check out a lot of technical statements.

    I read Tim F.'s post where he linked Howthingswork.com about the lights.

    They say typically the bulbs run at about 7-8 ohms and the shunts when activated run about 2-3 ohms. Thus a difference of about 5 ohms less. As you point out the lessening of total resistance will up the current and increase the voltage across the remaining bulbs, but not as much as a shunt that is completely shorted.

    The net resistance of a 1/2 string of 50 bulbs using the above information is 400 ohms. With a nominal 120V circuit that's 2.4 volts, so the bulbs are actually under-voltage a little already.

    Each bulb that gets burned out and replaced by a shunt reduces the string resistance by 5 ohms. Thus, full string of 50 is 400 ohms, 1 bulb out = 395, 2 bulbs out = 390, etc. Working ohms law on this you get
    Full string of 50 / zero shunts = 2.4 volts per bulb
    49 bulbs, 1 shunt = 2.43 V
    48 bulbs, 2 shunts = 2.46 V
    47, 3 = 2.49V
    46, 4 = 2.52V
    ...
    40, 10 = 2.72V

    therefore you can have 5 bulbs out of 50 in the half-string out before you even get to the nominal voltage rating of the bulbs, at the highest line voltage (120V). At 110V, you can probably have 9 bulbs out.

    Light bulb life at the rated voltage is dependent upon wattage...
    your typical 100W ordinary bulbs are like 1000 hours and 40 watt bults around 2000 hour life.

    For these little bulbs, lets asssume at least 5000 hours life.
    That means some will last 1000 hours and some will last 10,000 hours.

    A Christmas season, of 30 days, 8 hours a day is only 240 hours.

    So even running the bulbs 10% over the nominal voltage won't burn them out like hotcakes.

    I wouldn't worry about a few bulbs being out and causing the others to go quickly.

    When I get a string with a couple or three burned out bulbs, I go ahead and use it without worry or without trying to fix it. If its got four or five burned out bulbs before it goes on the tree, well, I retire it, and that's probably needlessly conservative. If it gets several burned out bulbs when in use, its no big deal, it should easily last the season.

    So, Nick, I think you're overly concerned about the burned out bulbs causing the others to burn out quickly.





    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    PM me (with your e-mail address) for a copy of the BT3 FAQ current vers 4.13

  9. #9
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    Loring,

    I can't explain it in theory, but we currently put up 32,000 lights, mostly mini's and I can tell you from much experience that having 5 bulbs out will definitely cause the string to fail before the end of the season. They might not go out "like hotcakes" but the string will eventually fail.

    Now a 20-light string, it only takes a few bulbs before the string goes into what I call "meltdown", where the string goes bad, and upon examination, virtually every bulb is burned out, some so violently that the formerly clear bulb looks like it has a mirrored finish.

    -Tim

  10. #10
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    quote:Originally posted by JR

    How would you create a 5' star? What kind of lights would you use? How would you form the star?

    I've thought about using those flexible tubes from the HD lighting section (you know, the kind used for accent lighting on bookshelves or display cases.). Would that work?
    Not quite sure what you're asking. I made one years ago for my parents with the multifunction lights like you describe (see http://www.plymouthlights.com/star.htm). If by "flexible tubes" you're referring to rope light, that would be another viable option. Rope light is available in chasing varieties as well as solid colors. Menards has a really good selection of it in the Christmas department, otherwise check out www.actionlighting.com.

    -Tim

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