Halogen bulb keeps burning out. ??

Discussion in 'General Electronics Chat' started by bjohnson75, Jun 7, 2016.

  1. bjohnson75

    Thread Starter New Member

    Jun 7, 2016
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    Hello,

    I am working on an old comparator, and I have changed the light circuit to 12VAC to use an FDT halogen bulb. The bulb is 12V 100W, and I am using a 120V to 12V 150VA control transformer to power it. The bulb is burning out right around once a week. Can anyone give me an idea as to why? Any direction would be greatly appreciated!

    ~Thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Sounds like the transformer output voltage may be too high.
    Do you have a multimeter to measure the voltage?
     
  3. bjohnson75

    Thread Starter New Member

    Jun 7, 2016
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    Transformer output is 12.36V. I measured current to the load on both wires, and it is 8.1A and 7.5A
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Did you touch the bulb with your hands?
     
  5. bjohnson75

    Thread Starter New Member

    Jun 7, 2016
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    Nope. I use the plastic that it comes in or a Kimwipe, which is like a small paper towel.

    I'm wondering if it isn't the socket. I'm trying to find a replacement, but it's proving to be difficult.
     
    Last edited by a moderator: Jun 7, 2016
  6. crutschow

    Expert

    Mar 14, 2008
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    There's something wrong with your current measurement.
    The current on both wires has to be the same since they are in series.

    I don't see how the socket could be a problem.

    What is the problem is a real curiosity.

    Who is the bulb manufacturer?
    I had my original halogen bulbs on a new microwave burn out prematurely.
    The name brand bulbs I replaced them with are lasting a lot longer.
     
  7. Soogs

    New Member

    Jun 7, 2016
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    These lamps usually only have an average life of about 50 hours or so.
    a lot of halogen lamps in the last couple of years have really dipped in their life expectancy quality.

    how long are you running this lamp for and is it for sustained periods or is it intermittent use?

    I work in the lighting industry so i can help maybe with the lamp side of fault finding.

    Soogs
     
  8. bjohnson75

    Thread Starter New Member

    Jun 7, 2016
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    It is an Eiko FDT bulb
     
  9. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    When you mount the bulb. Is the filament in a vertical or a horizontal position? Hint: horizontal is always better.

    Also, low voltages tend to affect a halogen bulb's useful life.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Replace with an LED and be done with it.. ;)
     
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  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    As @cmartinez points out, a halogen bulb relies on high temp, thicker glass (usually quartz) with that cools slowly an some halogen gas in the tube - this allows the tungsten to re-deposit on the filament each time it is turned off. So, short cycling of a halogen bulb will kill (turning it off before the glass has time to warm up). Likewise, running it at low voltage so it never warms up will also kill it. Also, running it in an area with forced cooling if the bulb was designed for ambient will kill the bulb. To see if any of these three issues are shortening the life of the bulb, look for dark/black/gray deposits inside on the glass (tungsten vapor depositing on the glass instead of back onto the filament.

    Running in small enclosures will kill it (Because it overheats or, if forced air cooling, it never reaches operating temperature).

    Vibration is also bad.
     
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  12. bjohnson75

    Thread Starter New Member

    Jun 7, 2016
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    @mcgyvr.. I've looked into it, and I can't find an LED that puts out 3000 lumens in such a small package.

    @GopherT... I will make sure it doesn't get cycled without proper warm up. It is in a smaller space with not much air flow. The glass looks like it has a dark gray blotch of paint on it when it blows. It isn't just breaking the filament.
     
  13. #12

    Expert

    Nov 30, 2010
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    The sockets are responsible for getting rid of a significant amount of heat. Corrosion causes more heat at the contact point instead of less heat.
    I would also mention that the power line voltage at my house is 250.1 VAC, rated 240VAC +/- 5%.
    Putting a buck transformer in series with my 115V rated HPS lamps increased their lifespan from 2&1/2 years to, "I don't know". I've never burned one out in the 13 years since I bucked the power voltage down from 125 to 109 VAC.
     
  14. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    I'm assuming this is an optical comparator, we left ours on all day once it was light. The heating and cooling of the bulb was harder on it than leaving it on.
     
  15. wayneh

    Expert

    Sep 9, 2010
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    Interesting point (in #13, from #12!). At my house, my HF meter shows ~119.5±1V every time I've ever looked over the last 25 years. It might be even tighter than that.

    Where did the nominal voltages for our power come from? I mean we call it 110 or 120 interchangeably, or 220 or 240. Why is the nominal voltage so fuzzy?
     
  16. #12

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    Nov 30, 2010
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    Because it has changed several times over the decades. There is a Thread here (somewhere) with charts.
     
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  17. RichardO

    Well-Known Member

    May 4, 2013
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    I am with you on this question... You forgot to mention 115 and 230 volts...
     
  18. wayneh

    Expert

    Sep 9, 2010
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    Yeah, I vaguely recall that. So the current nominals are 120/240 and the lesser values show up because of older equipment still on line?
     
  19. #12

    Expert

    Nov 30, 2010
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    I have transformers marked, "120/208/230"
    I have water heater elements marked, "240 VAC".
    I have a Fender Guitar amplifier with an accessory outlet marked, "115 volts".
    My 1979 Clothes dryer had to be converted to a 120V rated Calrod heater instead of 115V rated coiled nichrome so the heater would last more than 3 weeks.
    Engineering is always a series of compromises.:(
    If you live in Gnaw Bone Kentucky, you have no reason to expect the same voltage as La Vegas.
     
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