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Xmas: 50 lights on and 50 off

Discussion in 'Electronic Basics' started by W. eWatson, Dec 16, 2011.

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  1. W. eWatson

    W. eWatson Guest

    I started putting up outdoor Xmas lights (small candle shape) today, and
    noticed 1/2 the string, 50, probably 100 in total, were out. Nicely
    divided into two halves. I took the string to the h/w store to see if
    they knew what happened. Nope. They just refunded my money. They may
    have been blinking lights.

    This afternoon I went out to put up a string of blinking lights, maybe
    1" tall and upside down U shaped. They were all blinking. When I raised
    them on a pole, 50 stopped working. I counted them. What's going on?
    Both, I think, had 3 wires. The last set certainly did.
  2. W. eWatson

    W. eWatson Guest

    Yes, likely so, but then which one? I thought the three stringers
    somehow got around that problem.

    I thought I found out a year ago something that explained all this, and
    a way to repair them quickly. I don't see a bookmark on it, so off to

    Ah, here's a hint. Fuses. There are two in the plug, which indicates to
    me that a fuse could have blown.

    Ah, there's a tester than only requires one to slip a bulb over a hole.

    I see the avg life for bulbs in cheap strings ins about 3 years (seasons).

    Here's a "quick" tester
  3. Yes.

    We still have lights from at least forty years ago. I can't remember when
    they were bought, I can remember the serial strings where if one bulb went
    bad the whole string went bad, so sometime in the sixties the non-series
    lights came into the house. And they've stood up well.

    The small bulbs of more recent origins look nice, but yes, they are
    trouble (at the very least bad contacts, unlike the screw in bulbs of old)
    and of course, result in a semi-serial arrangement, back to "which is the
    bad bulb". But they are cheap, which has its advantages, but also the

    LED bulbs are down to what good Christmas lights used to be, they only
    seem expensive compared to the really cheap small throwaway strings of
    recent times. Buy a set of LED Christmas lights, and they'll last
    practically forever, just like those 1960s strings that are still running
    fine. But unlike the old lights, the LEDs will take forever before a
    light burns out, since they are LED, and unlike a lot of uses, the lights
    only get used for a couple of weeks each year, so the life span of the
    LEDs is nearly infinite.

  4. Desireless

    Desireless Guest

    lol I hear ya.
  5. Guest

    Most now have bulbs that fail short (or some other mechanism) so that one
    burned out bulb doesn't make the whole string go out. A loose bulb still
    opens then entire (half) string, though.

    To fix:

    1) Swap each bulb with a new bulb. Use one spare, replace first bulb, take
    that one and move to second, continue rotate left. Assumption #1: Only one is
    bad. Assumption #2: The string itself isn't bad.

    2) Get a non-contact voltage probe. Electricians use these things to check
    for live circuits. Move it down the chain until it lights up.
    Two? Both sides of the line (non-polarized plug)?
    You can get the non-contact testers at the HD or Lowes for about a third of
  6. Guest

    I have ornaments my parents bought for me ("ooh pretty") from 50 years ago
    that have been used every year since. Most of the (unlit and non-tinsel)
    ornaments are hand-made and >30 years old. I throw out lights as soon as they
    start making trouble. They're too cheap (the day after Christmas) to bother
    with or risk.
  7. W. eWatson

    W. eWatson Guest

    I bought a Light Keeper Pro at an ACE h/w store yesterday. It isolated
    the problem to the first four bulbs in the string that was out. My
    problem may now be finding four bulbs. I guess I can cut them out of the
    string and solder things back together.

    Our local ACE store was out but selling them for $22. I happened to be
    on a short trip 15 miles away and found them at an ACE for $17. One of
    our local stores sold them at Xmas time,but was out. Not an ACE.

    Interesting unit. It can solder pins down the string.
  8. ehsjr

    ehsjr Guest

    You could, but that would cause other bulbs in the remaining string
    of 46 to burn out prematurely. Also with a 3 wire string, you need
    to be able to figure out where to connect the wire (or the resistance
    described below to bypass the open bulbs. With some of the strings
    I've seen, the twisted wires make that too damn hard in my opinion.

    Regarding premature burnout and resistors to replace the bulbs:
    Each bulb in the original string of 50 drops a certain amount of
    voltage. If the original string contains only bulbs and wires, then
    each bulb drops ~ 2.4 volts (120/50). With 4 bulbs gone, you want to
    find another way to drop ~9.6 (4*2.4) volts. Otherwise, the 46 bulbs
    are each subjected to voltage a bit higher than normal, and will
    burn out more quickly.

    Probably easiest to buy another string, but if you want to proceed
    and use a resistance to drop the voltage, you'll need to measure the
    current drawn by a fully operational string. That will be I in the
    formula E = IR. Solving for R: R = E/I. E is the voltage drop,
    assumed to be 9.6 volts. It would be better to measure the voltage
    drop across 4 bulbs in the fully operational string, and use that
    measurement for E in the formula. R is the resistance required to
    drop E volts at I current. The wattage dissipated would be I^2*R and
    the resistor(s) would need to be rated at least twice that for a
    safety factor. Since the resistance might touch flammable material,
    you probably want a lot higher rating. More on that follows.

    I don't know the specifics of your string, so I'll make up a value
    for I: 200 mA. Using 200 mA and 9.6 volts, the required resistance
    would be 9.6/.2 or 48 ohms, and the power dissipated would be 1.92
    watts. I'd use 5 ten ohm, one watt resistors in series. That way
    the dissipation would be spread across 5 resistors which would keep
    the temperature lower. Whatever the actual number turn out to be,
    you want to spread the heat out over a large enough area to keep
    the temperature well within safe limits.

    Replacing the bad bulbs with identical new bulbs, or replacing
    the string, avoids all of that.

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