need help with unusual household lighting circuit

Discussion in 'The Projects Forum' started by johnwtfd, Dec 28, 2010.

  1. johnwtfd

    Thread Starter New Member

    Dec 28, 2010
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    I am trying to repair an old chandelier. It has two 120 volt AC circuits, one simply powers a medium base socket. The other powers a ring of 12 christmas mini lights (incandescent). These are wired to stick out of the top of 12 glass "candlesticks". both circuits are on dimmer switches. The owner of the chandelier was having trouble with the christmas lights blowing out, sometimes even if the dimmer was turned up just a bit. I'm trying to make them be stable , at least with the dimmer on low. They were originally wired in series. The guy at a light bulb shop told me to wire them in parallel. I did this using 18 gauge wire. But now they blow out even easier. I tested the circuit with a continuity tester and it checks out fine. Any suggestions on how to make this work? I'm just a lamp repair guy. Perhaps this isn't the right forum for this question but I thought I'd give it a try.
    Thanks!
     
  2. someonesdad

    Senior Member

    Jul 7, 2009
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    Well, if a lamp rated for line voltage blows out, either the lamp is defective or the voltage is too high, resulting in too much current. You don't give any pictures or schematics, so we can't troubleshoot what's sitting in front of you.

    If it was me, I'd take the dimmers out of the circuit and see if things can first be made to work connected directly to the line. You can check that the circuit is properly wired first with an ohmmeter. Check obvious things too, like making sure that the lamps are really rated for line voltages. Then test the dimmers on a separate circuit to make sure they're working correctly.

    If you can, power things up with a Variac and monitor the current levels -- this can save you from blowing out lamps. If you know the power rating of the lamp in watts, the current will be the power divided by the RMS line voltage.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Christmas lights are typically 24VAC (mini bulbs) or around 3VDC (LED)

    The step down transformer for the mini lights may have had a horrid failure, or a short exists, or somebody pulled a Tim Allen (rewired it for more power). :D
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I don't see a problem if it was properly converted to take 120V Christmas lights.

    An ohmmeter is your friend here but don't measure anything with lamps in the sockets as a cold incandescent lamp will read near a dead short as you probably already know.

    Make darn sure the wiring is right (can't see how it could be wrong enough to blow modern bulbs) then try testing one at a time. I think you may find something really obvious that's been staring you in the face the whole time. I will assume you know that, if the fixture is grounded, any leakage back to the metallic part could interfere with the integrity of the dimmer?

    I remember the old 7W Christmas bulbs that were all in series, they were sure a lot easier to repair than the modern twinkle light sets but I'll still repair rather than replace them unless the wiring is messed up.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I didn't see any mention of a transformer. I suspect he has a big mismatch between rated bulb voltage and applied bulb voltage. With 12 bulbs, the simplest solution would be a dozen C7 bulbs in parallel, but they may be too big.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    The really old C7 bulbs varied depending on how many was in a string. It I recall most were rated for 6V if in a string of 25 or, more commonly, 8V if in a string of 15. You've got to remember that these haven't been around in the series configuration for probably 70 years.

    Modern twinkle lights vary by the number in a string as well, 2.5V each for a string of 50 or 3.0V for a string of 35 isn't uncommon but they're extremely current sensitive, if you don't get the right replacement bulb it will either barely light or it'll burn right out.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    All the incandescent C7 bulbs that I found when searching the Internet were 120V.
     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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    That's because you weren't around back in the days that they were in series strings. You can still find them on specialty sites but due to the cost and frequent failures they're only really sold to collectors.

    Plenty of modern bulbs with the same base that would satisfy a series string but why bother?
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I'll be 70 in March. I remember series strings. I just didn't find any low-voltage C7s in the limited search I did. I think 120V parallel-wired would be better anyhow (even if you could find 10-12V bulbs). Series strings are a PITA.
     
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I'm sure by now he's figured it out and all is well.
    I do like it when people post back and say they've fixed something though.
     
  11. johnwtfd

    Thread Starter New Member

    Dec 28, 2010
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    Thank you all for your thoughtful replies. I've been dealing with lots of visiting family this week so I haven't stayed on top of this.
    You are correct Ron, there is no transformer. And the glass candle sticks are too small for C-7 bulbs. The opening is about 3/8" diameter. So I think I have to use the mini lights (incandescent). Please see the attached photos. These mini lights are 2.5 volts each. Do I need a transformer? If so, any suggestions on one small enough to hide in this fixture and where to buy it? I've rechecked the wiring by putting one ohm meter probe on the power source wire and the other probe on each socket contact, then switching the first probe to the neutral wire . The wire is 18 gauge.
    Thanks again! I apologize if I'm not up to speed on some of this.
     
  12. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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  13. johnwtfd

    Thread Starter New Member

    Dec 28, 2010
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    Thank you. That website is a great resource. Unfortunately, the CA bulbs in the link are too large to fit into the glass candle sticks.
    But I have found on line some strings of 10 mini lights, though it's hard to tell for sure from the product description. Anyway, if I buy 2 of these and make a string of 12 I think I should be okay.
    Thanks again.
     
  14. marshallf3

    Well-Known Member

    Jul 26, 2010
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    You can get twinkle lights in higher voltages but you better move fast as it won't be long until they clear all the Christmas stuff off the shelves. A sting of 20 will typically have 6-8V lamps in them and the current draw is low enough that a simple resistor could be used to lower the voltage. In the meantime there are plenty of sources for miniature bulbs, http://www.jameco.com comes to mind or http://bulbs.com or even http://www.atlantalightbulbs.com/
     
  15. johnwtfd

    Thread Starter New Member

    Dec 28, 2010
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    Thank you much! Those are good resources.
     
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