bulbs burn then smoke and go out.

Discussion in 'Landscape Lighting' started by n2h20, Jun 8, 2005.

  1. n2h20

    n2h20 LawnSite Senior Member
    Posts: 503

    I have a client whos lighting in the front of house does not work. about 10 lights with a cheapo transfomer... (300 or 500 watt) so she calss me and tells me that if she replaces a bulb it burns right out. SO i tried it and the buld burns on the inside (kind of yellowish smoke) then gets brights and burns out.. what could cause this? i have not checked the wiring under ground but assume it is ok. would this be a transformer problem?
     
  2. NickN

    NickN LawnSite Bronze Member
    from Alabama
    Posts: 1,010

    Sounds like too much current.Measure the current flow at the fixture and see what you get.Remember,current must be measured "in line".
    Take your power (wattage) and divide by your voltage.That is the maximum current flow you should have with 0 resistance.If the bulb isn't rated for that,it will blow.
    Also,measure the voltage at the fixture.Divide the power(watts) there by the voltage and see what you've got.Then check the amp rating on your bulb.
     
  3. n2h20

    n2h20 LawnSite Senior Member
    Posts: 503

    so is that saying that if i had a 500 watt transfomer and only 1 20 watt bulb it would blow?
     
  4. dvmcmrhp52

    dvmcmrhp52 LawnSite Platinum Member
    from Pa.
    Posts: 4,205




    Most likely it would, transformers should be close to the total wattage of all bulbs running off of it otherwise the life of the bulb is decreased.
     
  5. NickN

    NickN LawnSite Bronze Member
    from Alabama
    Posts: 1,010

    <i>so is that saying that if i had a 500 watt transfomer and only 1 20 watt bulb it would blow?</i>
    No.The current is what's important.Wattage is power.Yes,a 20 watt bulb off a 500 watt txformer will decrease it's life cycle,but it won't blow like your talking about.If you're pulling too much current(amps) at the fixture,this will cause the bulbs to overheat and blow.Think of current flow like water going through a hose.It flows,negative to positive,negative to positive,etc.,,Voltage is consistant and is felt across the circuit,but current flows like water.Since the negative particles are attracted to the positive particles,you get flow from negative to positive.Now,if for some reason the current flow were disrupted or was too high at that fixture,POP,out goes the bulb.
    Check the current at the fixture and look at the specs on your lamp.I'm guessing the current at that fixture is higher than the lamp amp rating.
     
  6. Frog Lights  LLC

    Frog Lights LLC LawnSite Member
    Posts: 191

    Check the voltage at the bulb. maybe too high.
    Check the voltage rating of the bulb , maybe she bought 6 volt bulbs. Wattage is not a facture in this case.
     
  7. dvmcmrhp52

    dvmcmrhp52 LawnSite Platinum Member
    from Pa.
    Posts: 4,205

    O.K. frog and Nickn,
    How would the amperage at the fixture be too high?
    How would the voltage be too high at the fixture outside of the possibility of the customer buying the wrong bulbs?


    Not busting here I'm interested in your response...............
     
  8. NickN

    NickN LawnSite Bronze Member
    from Alabama
    Posts: 1,010

    A short in the fixture would cause the current to increase.A bad transformer could cause a current increase.Even a bulb with too little voltage could(just a bad bulb,not necessarily the wrong one.).Current is inversly proportional to voltage(E=IxR),so by dropping the voltage,the current increases.Same goes for resistance and voltage.Substitute that with (P=IxE) and you can see that Power(watts) is also inversly proportional to current(I) and voltage(E).
    Take P(watts) and divide by E(volts) and you get the max current(I).If he has a 500 watt transformer and 15 volts,his max current would be 33.3 amps.I'm assuming his lights are wired in parallel.In parallel the current increases with each fixture installed(It=I1+I2+I3,etc.,,)(as does resistance) and the voltage remains near the same.(Think two 12 volt batteries in parallel)So,if a fixture were bad,it could cause an increase in current which would be too high for the lamp to take.
    I'll try to come up with some basic electronic formulas for this page as time allows and explain different laws and functions.It helps that I have an electronic engineering degree.:D
     
  9. NickN

    NickN LawnSite Bronze Member
    from Alabama
    Posts: 1,010

    Another example of what could have happened is in the drawing here.A short is created across the wire(in red),so instead of the circuit being parallel,it is now a series circuit.The short will provide very little resistance,approx .1 ohm.So,using ohms law 15volts/.1ohm = 150 amps.This would be way over the 33.3 amps and would cause his bulb blow.

    edit:The drawing didn't show up too well.I had to resize it and lost alot of info.
     

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  10. dvmcmrhp52

    dvmcmrhp52 LawnSite Platinum Member
    from Pa.
    Posts: 4,205

    Thanks NickN,

    I'm following you somewhat.........No electrical engineering degree here........LOL.

    But........one thought for me was a short, but I think ALL low voltage lighting has shorts to a degree..........

    However, for arguments sake let's say she only had a 100 watt transformer, would it be as likely to have too much current for the specific bulbs even with a short?

    Again, I'm trying to get it straight for myself............
     

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