Simple 12vdc led flex strip power from 120vac?

Discussion in 'The Projects Forum' started by playfair, Apr 17, 2011.

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  1. playfair

    Thread Starter New Member

    Apr 17, 2011
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    Hey guys- First post here! I'm a mechie by trade, but have always had a fondness for electronic stuff. Found this site looking for info on a project I'm doing, and was amazed by the good stuff here (one could spend months reading!). However, searching hasn't returned my exact situation.

    What I want to do is replace an aged 120vac rope light used for ambient cove lighting with flexible LED strip light around the ceiling of a room. Length is around 40' total. It is controlled via a remote electronic dimmer.

    The crown molding the lights reside in has barely enough room for the 120v outlet that currently powers the lights, making the addition of a transformer difficult at best. I'm hoping there's a way to keep this simple, yet continue to allow the dimming feature.

    The strip I want to use is a 12v series/parallel configuration of leds, cuttable every 3 lamps.

    The total length in 1 run is limited only due to the amount of current the flex PCB can handle (1.2 amps per meter).

    What I'd like to do is rectify ac with a suitable bridge, smooth out the ripples with a cap, and cut the total length into 10 similar sections which will be in series with each other so the 120v is divided by 10.

    I don't want to use a capacitor to reduce the voltage because I need this to still be dimmable. Total current in 10x 4' sections should still be under 1.5 Amps. The stuff isn't cheap (even directly from China), so it's best I catch an error in the plan here~

    Thanks for any assistance!
     
    Last edited: Apr 17, 2011
  2. playfair

    Thread Starter New Member

    Apr 17, 2011
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    Funny, the images I linked to worked fine in preview, but not once posted!
    The first is the physical layout of the strip, second is a schematic of the strip, and the third is a schematic of what I'd like to do.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    Begging everyone's pardon, but we do not support circuitry directly attached to the mains. There is no protection from lethal voltage. That is why commercial stuff carries certificates to attest some protection against shock.
     
  4. playfair

    Thread Starter New Member

    Apr 17, 2011
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    I'm sorry. This application would be out of reach, but also sealed and fuse protected.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U shud use standard 120V Led drivers that are available out there. check out the pdf
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    If this were not a public forum, there would be no problem. Our audience is of all ages, abilities, and has every level of caution and understanding. For that reason, we have to limit discussion of circuits isolated from the mains.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    In Canada most PA systems use 70V for the speakers. Then each speaker has a transformer that sets its power.
    In Canadian schools the PA speaker voltage is limited to only 25V to avoid zapping a kid who might be crawling around in the ceiling space.

    A little kid might read this forum to see a transformer connected to the mains and try it. He will probably be killed. Same for the rectifier that feeds these LEDs.

    Do I dare talk about twenty 9V batteries in series?
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    We have a consistent policy about circuits that run directly off the line.

    We can't guarantee perfect safety in everything, but we have decided that line-operated circuitry is too dangerous.
     
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