Low Voltatge Lighting Issue

Discussion in 'Electrical Forum discussion & Blog' started by c6man, Aug 10, 2007.

  1. c6man

    c6man New Member

    Messages:
    3
    Hello,

    I cannot for the life of me figure out what is going on and I'd appreciate some advice.

    I have a low voltage outdoor lighting setup that was installed when the house was built. I have been having problems, in recent years, with lights not working.

    At one light when, using a multimeter, I read 11.1 volts where the bulb plugs in. However, the bulb will not light. If I move the fixture to a point very close to the source, for testing purposes, I still read 11.1 volts, and the it lights up. I don't understand how I can have the same voltage reading, but the bulb won't light further down the wire.

    Any thoughts?
  2. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    Central Florida
    One possibility is that there's a high-resistance point in the circuit. Your multimeter places almost no load on the circuit, so the voltage drop through the high resistance is negligible. With the bulb in the socket, however, the voltage drop will be much higher, and little current will flow through the bulb. If you can measure the voltage across the bulb with the bulb in the socket, or otherwise in the circuit when you measure the voltage, you can see this effect.

    Cause of the high-resistance point could be corrosion in the wire or at a connection somewhere in the circuit.
  3. frenchie

    frenchie Jack of all trades

    I feel especially silly posting this after Mikey's comment, but... sometimes it's the obvious thing...

    Not sure what kind of sockets you have - but often when they get old, contact points get less "springy", and you don't actually have a connection to the bulb.
  4. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    I'm glad you cleared that up, but I liked my interpretation a lot better.
  5. c6man

    c6man New Member

    Messages:
    3
    Thank you for your replies.

    The issue isn't with the light itself as I have tested with a brand new fixture that again works when connected next to the box, but doesn't (even with the same voltage output) when connected down the line. If it were a problem with the contacts for the bulb, I don't think this is the behavior I would see.

    After some further tests I have found more interesting behaviors. I have 3 fixtures (F1, F2 and F3). If I have a bulb connection at F1, F2 & F3 do not register any voltage at the light as measured on the multimeter. If I remove the bulb from F1, voltage can be measured at F2 & F3. Again under no circumstances can I get any fixture/bulb to light at any of the fixture installation points. Could a short somewhere cause this? This might fit in with Mikey's thoughts.

    Thanks again.
  6. hj

    hj Moderator & Master Plumber Staff Member

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    wire

    A short would trip the breaker in the timer. You may have a splice in the main wire and that would act the same as a corroded connection at the light, but would affect all the lights on that portion of the wire.
  7. c6man

    c6man New Member

    Messages:
    3
    I've got it working.

    I found a connection just prior to F1. This connection connected both F1 and was a split for the wire running to F2 and F3 across the yard. Whoever installed the line, just taped over the splice and buried it, but never really protected it. So the wires there were quite corroded. I did a new splice and then got some wire nuts that are made to be put underground (they have silicon in them). Taped over all of that. Working great now!

    The fact that voltage was still getting to the lights really threw me for a loop.

    Thanks all for the advice.
  8. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,714
    Location:
    Central Florida
    You've just discovered that voltage alone won't do the job. If you understand Ohm's Law, the fact that Power is (more or less) the product of Voltage * Current, and the fact that your multimeter draws essentially zero current when measuring voltage, you can easily see why your meter "worked", but the light didn't.

    But forget all that -- you found and fixed the problem, so pat yourself on the back (or have your Significant Other do that), kick back, and celebrate :D .
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