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Dipped Beam Bulb

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by Spikeymikey, Dec 27, 2012.

  1. Spikeymikey

    Spikeymikey Member

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    Help,

    My right dipped beam bulb has blown, I have changed the bulb and ok but then blows again straight away, any ideas. It is the correct bulb.


    Spikey
     
  2. DY2

    DY2 Senior Member

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    Contacts clean and dry?
    Using a good quality bulb?
     
  3. OP
    Spikeymikey

    Spikeymikey Member

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    Yes bought 2 x lucas bulbs and both have blown
     
  4. Naraic

    Naraic Moderator

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    Have you got a multimeter?
     
  5. OP
    Spikeymikey

    Spikeymikey Member

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    No I have not
     
  6. Miffy

    Miffy Senior Member

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    I think the idea was to verify the voltage as a dodgy regulator could be allowing an over voltage situation
     
  7. Naraic

    Naraic Moderator

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    As above...a useful piece of kit for finding faults etc. Cheap on Ebay...get one.
     
  8. television

    television Always remembered RIP

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    The running voltage should be around 14 volt max, if over this then a reg pack issue but not that easy as a water cooled alternator
     
  9. whitenemesis

    whitenemesis Senior Member

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    Why would over-voltage only blow one dipped beam lamp?
     
  10. wireman

    wireman Senior Member

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    If both lamps were bought at the same time (same batch) I would suspect the bulbs.

    As to why would overvoltage blow just one lamp, I suggest that it would not, but would blow as many as it could and that they would be noticeably very bright for those several seconds
    The over voltage condition would have to extend for some time to take out a new bulb or be of very high magnitude, if such a condition ever arose it would not be just one lamp that failed, damage to the entire vehicles electronics would be almost a certainty.

    A defective regulator usually means the alternator brushes are worn, this tends to result in lower than normal average voltage with very short spikes of over voltage being generated as the duff/bouncing brush makes contact. The spikes would be clamped to an acceptable level (to a lamp bulb) say <17v or so by the battery, it is not very likely that this failure would kill off lamps.
    Loss of the earth connection to the regulator (inside the package) will result in the alternator putting out as much power as is possible, however this condition is almost an impossibility on alternators with an integrated regulator, it is a real and present danger in much older systems with external control gear, the last time I saw this was on a seventies Jag 420G with a Lucas 11AC alternator, every lamp on the car failed. I have dealt with similar problems on Prestolite, Butec and Delco charging systems.

    A defective battery connection may also be causal of such voltage excursions but this fault is normally accompanied by poor starter motor performance.

    I have found Lucas lamps to be reliable and have them on my mental list of usable parts, perhaps I should consider putting them in the second division.
     
  11. Uncle Benz

    Uncle Benz Senior Member

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    It is important too not to touch the glass while fitting the bulb. Finger residue on the glass can lead to premature failure.
     

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