Fluorescent tube backlights - project ideas?

Discussion in 'General Electronics Chat' started by GopherT, Jan 17, 2015.

  1. GopherT

    Thread Starter AAC Fanatic!

    Nov 23, 2012
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    I just pulled these backlights from a dead LCD TV. Anyone have an ideas how to test them and what I could do with them for a project.

    I have a pair of HV transformers for each one. They were connected with one transformer on each electrode on each tube (10 transformers). I think they need 24v pulses on each transformer input which are out of phase with each other.

    Tubes have a total length of about 50 inches each and about 3/16" diameter. Looks easy to bend but may blow out or stress crack if I heat it. Heat May also damage the white phosphor powder.

    All ideas are welcome.

    image.jpg
     
  2. ian field

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    Oct 27, 2012
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    Florescent tubes contain a few tiny drops of mercury - very toxic, look up "hatters disease".

    If you break the tubes, you probably won't even see where those tiny droplets of mercury went.
     
  3. Dr.killjoy

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    Apr 28, 2013
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    What about powering the inverter board .. Sorry you said dead lcd not what was dead ..
     
  4. ronv

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    I have some CFLs under the kitchen cabinets for light. It's been a long time, but I think it is high frequency that excites them along with high voltage. Mine wouldn't work with long (5ft.) wires going to them.
     
  5. GopherT

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    Thanks for your concern (honestly). I would surely do any glass-bending in an outdoor setting. If possible, right next to the rabbit hole. I am sure Alice would approve.

    The inverter board is my only option for now - I was hoping for something more straightforward. There is a 20-pin connector and I have only figured out the first 8 pins (4 @ 24 v supply and 4 @ ground). After that, various enable and power ok and current sense. Seems like Samsung is pretty concerned with the high-voltage section of their TVs.
     
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  6. Dr.killjoy

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    What was wrong with the tv??? Thats how I test tubes out .. But you could use a different inverter I think..
     
  7. GopherT

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    I was told that the TV was not starting and it was replaced. My son took it apart to scrap it before I got home from a business trip. I haven't the foggiest idea of what happened to the TV.
     
  8. spinnaker

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    Gopher is a ChemE if memory serves.

    And I used to play with the stuff as a kid along with lots of other people my age. We are still here. ;)
     
  9. joeyd999

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    Yea. I used to take mercury to school and "distribute" it amongst my friends. We roll it around our desks all day, then I'd collect what ever didn't get lost/evaporate at the end of the day.

    Imagine that today! School on lock down, students quarantined, frantic gov't officials running around in hazmat suits, terrified parents.

    I miss the olden days.
     
  10. GopherT

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    I played with mercury as well. I guess it explains why all of our kids think we are weird.
     
  11. tcmtech

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    No not really. Exposure to the inorganic type metallic mercury like what is used in CFL and other arc type bulbs is for the most part harmless to anyone unless you put it in a spoon and heated it to its vaporization point and inhaled it and even then it would be hard to get a high enough dose unless you smoked contents from a lot of bulbs on purpose.
    To be honest you could literally drink a teaspoon (~200 grams!) of the stuff directly and still not get enough to stay in your system long enough to harm you. You would however get silver stripes in your underwear for your efforts.

    Worth a read.

    http://www.atsdr.cdc.gov/phs/phs.asp?id=112&tid=24

    If you want the version that accumulates in your body you need methyl mercury which is the organic mercury compound but that's not used in lighting devices. :(

    http://en.wikipedia.org/wiki/Methylmercury

    And if you want to mad as a hatter you will need Mercury nitrate, another organic mercury compound, not metallic inorganic 'light bulb' mercury.

    http://en.wikipedia.org/wiki/Mercury(II)_nitrate
     
  12. GopherT

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    Kind of true, but it seems you have selected your favorite parts of the cdc article to convince yourself or others that mercury metal is not dangerous. You were right, Ingested mercury does not pass the stomach walls or intestinal wall easily. As stated in the cdc article, only 0.01% passed into the body when a person ingested 200 grams of mercury.

    However, the same cdc link says that 80% of the mercury vapor inhaled is absorbed into the blood stream when it is inhaled. Amounts are low but I wouldn't want to spill a gram in my child's bedroom carpet or in the concrete basement floor if anyone spends a lot of time there - especially if the windows/doors are closed in the air conditioned summer or heated winter.

    From cdc link
    When you swallow small amounts of metallic mercury, for example, from a broken oral thermometer, virtually none (less than 0.01%) of the mercury will enter your body through the stomach or intestines, unless they are diseased. Even when a larger amount of metal mercury (a half of a tablespoon, about 204 grams) was swallowed by one person, very little entered the body. When you breathe in mercury vapors, however, most (about 80%) of the mercury enters your bloodstream directly from your lungs, and then rapidly goes to other parts of your body, including the brain and kidneys. Once in your body, metallic mercury can stay for weeks or months. When metallic mercury enters the brain, it is readily converted to an inorganic form and is "trapped" in the brain for a long time. Metallic mercury in the blood of a pregnant woman can enter her developing child. Most of the metallic mercury will accumulate in your kidneys, but some metallic mercury can also accumulate in the brain. Most of the metallic mercury absorbed into the body eventually leaves in the urine and feces, while smaller amounts leave the body in the exhaled breath.
     
    Last edited: Jan 17, 2015
  13. tcmtech

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    Nov 4, 2013
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    What else did I say in my first paragraph? o_O

    Something about vaporizing it in a spoon and inhaling it and what not? :rolleyes:
     
  14. GopherT

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    Yes, but you are making it sound like mercury vapor can only exist if you heat it. Dispersing on concrete or carpet fibers can get some reasonable surface area and evaporation. into the room air, lungs, bloodstream and brain.

    It is slow, but if people spend significant time in the room, it will get extracted by their lungs. It accumulates and, even if slow, it still happens.
     
  15. tcmtech

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    I know it evaporates but its extremely slow under typical household temperature conditions.

    Heres what the level headed experienced people say.
    http://www.heracliteanriver.com/?p=246

    So unless you dumped a jug on your unreasonably over heated radiant heat floor continually agitated it with a mixer to keep it from coalescing into large drops or pools all while the room was hermetically sealed the odds are you are going to be just fine unless of course you ran out of oxygen first and died of asphyxiation. :rolleyes:

    What I am saying is as with every toxic substance there is a threshold exposure level based on quantity and time. Given typical everyday conditions and sources of mercury you are very very unlikely ever going to create a condition that exceeds the minimum time/quantity requirement. Especially so with a the amounts of mercury found in common lighting fixtures while in any average normally ventilated house. ;)

    You're a chemist aren't you? You should know this stuff. :p
     
  16. GopherT

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    I am, and I do. I have done extensive work on evaporation and that is why I mentioned concrete and carpet as a method of increasing surface area and, therefore, evaporation rate. I also emphasized that it was slow. But no matter how slowly it goes in, it never comes out. Live in the same house where there was a mercury spill long enough, you're going to inhale some mercury.

    If you disagree, fine.

    Now, does anyone have a project idea for these tubes?
     
  17. ian field

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    Strip lights running on 50/60Hz is ancient history - its been known for a few decades that the tubes are about 20% more efficient at 20kHz.

    You have to be a bit careful with the term "CFL" - the 2D pattern light in my smallest room claims to be a CFL, but it most certainly has an old style iron ballast - I know this because the dumbass electrician fitted the wrong one, the tube gave up after a month! After replacing that with an electronic ballast, I got away with about a year of further use from the damaged tube.

    The early electronic ballasts paved the way for the CFLs as most people call them, except for 110V types, there's no voltage boosting involved - the tube needs somewhere around 70 - 90V to strike, all the CFL PCB does is convert the mains to DC and chop it to a higher frequency and use a much smaller ferrite cored ballast.

    The CCFL tubes in a LCD screen are a bit different - they have no heaters for starting, and rely entirely on voltage to initiate ionisation. The striking voltage is around 1200V, and about half that when running.

    It worth looking through the LT appnotes by the late Jim Williams - among all the analogue stuff are a few notes on backlight design.
     
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