Post light trouble

Discussion in 'General Electronics Chat' started by LDF, May 16, 2015.

  1. LDF

    Thread Starter New Member

    May 16, 2015
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    I install low voltage exterior lighting. I have a customer who asked me if I would look at her post light which is 120v in line and controlled only by a photocell on the post itself. She said the post light only worked for a couple of weeks after they moved in and no longer works. I figured it was a bad photocell however when I removed the top of the post and checked the main wire, I was only reading 12 volts.
    Could a damaged wire be a possible cause for such a low voltage reading? The post is about 75' from the house.
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    784
    I think the clue might be in "low voltage lighting" - but most up to date ones use switch mode transformers, the output AC frequency might be too high for a typical multimeter to make sense of. The optoelectronics part most likely runs off a rectified, smoothed and possibly even regulated 12V DC supply - although I have seen purely mains rated control in the form of an LDR rated for mains, that fed a number of turns of resistance wire wound round a bi-metal strip that operated the contacts.
     
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  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    When it was working, what was the light bulb? If it was a 120V bulb, then the problem might be the triac circuit that the photocell controls. These can be taken out by the current surge that causes the bright flash when a bulb blows.

    ak
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,564
    2,379
    Some post lights also have the transformer and sense unit in the base and run up to the lamp with 12v.
    Max.
     
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