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Strange problem with low energy light bulb

Discussion in 'Electronic Repair' started by Seán O'Leathlóbhair, Jun 25, 2007.

  1. I am not sure if this is an appropriate group for this question. If
    not, please suggest a better one.

    I have a light in the house which I have wanted to switch to a low
    energy bulb for a long time. The hold up was that I needed a very
    small bulb. At last, I have found a small enough bulb but something
    odd occurred as soon as I put it in.

    When it is switched on, it works as expected.

    When it is switched off, it blinks every few seconds. So, I guess
    that there must be a problem with the switch If it is passing nothing
    then it would seem impossible for the bulb to do anything. I did not
    notice any problem with the previous incandescent bulb but I guess
    that if the switch is leaking a tiny amount, the filament would glow
    too little to be seen.

    I have a few questions:

    What is going on? Is a tiny current leaking, building up a charge in
    a capacitor somewhere until a sufficient voltage builds up to spark in
    the bulb and discharge the capacitor, and then the cycle repeats.

    Is it safe?

    Will it wear out the bulb very fast?

    Is it likely to be enough to replace the switch? (Actually three
    switches can turn this bulb on and off).

    Might I have to replace the wiring? (Much harder than just replacing
    the switches)
     
  2. N Cook

    N Cook Guest

    I am not sure if this is an appropriate group for this question. If
    not, please suggest a better one.

    I have a light in the house which I have wanted to switch to a low
    energy bulb for a long time. The hold up was that I needed a very
    small bulb. At last, I have found a small enough bulb but something
    odd occurred as soon as I put it in.

    When it is switched on, it works as expected.

    When it is switched off, it blinks every few seconds. So, I guess
    that there must be a problem with the switch If it is passing nothing
    then it would seem impossible for the bulb to do anything. I did not
    notice any problem with the previous incandescent bulb but I guess
    that if the switch is leaking a tiny amount, the filament would glow
    too little to be seen.

    I have a few questions:

    What is going on? Is a tiny current leaking, building up a charge in
    a capacitor somewhere until a sufficient voltage builds up to spark in
    the bulb and discharge the capacitor, and then the cycle repeats.

    Is it safe?

    Will it wear out the bulb very fast?

    Is it likely to be enough to replace the switch? (Actually three
    switches can turn this bulb on and off).

    Might I have to replace the wiring? (Much harder than just replacing
    the switches)

    --
    Seán Ó Leathlóbhair


    It may not be a switch problem but more seriously an animal , usually
    squirrel or mouse or rat has chewed the insulation along the wires going to
    the switch, now with charred insulation, so passing a bit of current - so
    get the wiring leakage/visually checked. Especially if you've had any
    unexplained fuses blowing or history of animal noises in loft or floor
    spaces.
     
  3. BH

    BH Guest

    Try the buld in another location. Give us moe information on the bulb.

    Bruce
     

  4. Thanks.

    Normally, I would immediately try to isolate the cause by moving
    things around but, in this case, I dismissed the bulb as the problem
    since I thought that if the switch was passing nothing when off (as it
    should) then there was no way the bulb could do what it is doing. If
    the bulb is at fault then it is not the only fault (or so I assumed at
    any rate).

    The brand of the bulb is Philips but I cannot tell you more until I
    get home and look at it. I will post again later with fuller details
    and the result of a test in another location.
     

  5. Thanks for the advice.

    We had some fuse problems many years ago but not on the lighting
    circuits. The problem was traced (by a proper electrician) to the
    ancient (bakelite) fuse box. It was replaced with a modern fuse box.
    The wiring was tested (but not completely inspected) at the time.
    Since then, we have not had any fuse problems. That was about 10
    years ago.

    I am not aware of any animal problems in the loft but, of course, that
    does not mean that there have not been any. Access to the loft is
    difficult since it is very small but not quite impossible. I will
    squeeze myself in and have a look.
     
  6. Ken Weitzel

    Ken Weitzel Guest

    Hi...

    Can't help wondering - it's not possible that one of those
    "switches" is a dimmer, is it?

    Take care.

    Ken
     

  7. A good question but no.

    It is a landing light. There are three switches, one at each end and
    a third in the middle where a small corridor from the bathroom joins
    the landing. All simple on off switches (well they must be changeover
    switches but, from the user's point of view, they are just on off).
     
  8. Ron(UK)

    Ron(UK) Guest

    Sounds like leakage to me, there may be a measurable voltage floating on
    the neutral. I has a similar problem with fluorescent emergency lights
    last year. If you are in the UK it might be an earthing fault.

    Ron(UK)
     

  9. I am in the UK.

    How does an earthing fault affect the lighting circuit? I thought it
    was just two wire. The earthing for the house in general was checked
    a couple of years ago when we changed the boiler. The gas engineer
    said that a change was required but I forget exactly what that was.
    The RCCB in the new fuse box is not tripping but does it apply to the
    lighting circuits?
     
  10. Scalp

    Scalp Guest

    Hi, this isn;t that uncommon a problem with low energy bulbs. Its
    probable that there is a voltage induced into the 'dead' circuit by
    cables running in close proximity to one another. Typically this
    occurs on long cable runs for hall/landing circuits.
    The way I'd bottom it is to use a DVM across the lamp socket & see
    what voltage is present. You shouldn't be able to draw any current (to
    speak of) from a capacitive or inductive coupling.
    What happens is that theres enough voltage for the tube to strike but
    no capacity to draw current, so it goes out until the voltage builds
    up again.
    You can buy suppression capacitors to overcome this (Note they are
    special devices - don't try to bodge it!) but sometimes just swapping
    with another LE bulb will do the trick.
    If the problem isn't as described, you'd better get someone in to
    check the wiring for contacts or earth problems.
    Dale.
     
  11. Yukio YANO

    Yukio YANO Guest

    On a cold wet miserable winter day in the early 70's. I was
    troubleshooting a newish car, that wouldn't start, that had just been
    serviced by a car dealership. a few days before. To cut a long story
    short, they lubricated the Point Breaker mechanism with a clear Grease
    that they probably used for years with no problems ! With 2 to 6 Amps
    flowing, the contact mechanism probably cooked off any wet or
    conductive grease. With the newer Hybrid Transistor switched points the
    DAMP grease appeared as a Dead Short to the few milliamps required to
    actuate the Transistor.

    I would suspect the switches (All three) are lubricated with a grease
    that is conductive enough read (dirty enough)to cause the problems
    indicated !

    The quick and dirty, to clear the excess grease is to replace the lamp
    in question with a 60 - 100 watt bulb and switch On and Off a few
    times. in the Off position any conductive grease will be burned away.

    Any fire Hazard, Not likely, after all these switches were manufactured
    and sold for years lubricated just like this, besides we are talking
    about a drop or two grease total ! If you are worried, replace the
    switches.

    If this doesn't clear the problem than you may have exessive
    capacitative coupling between the various conductors due to the
    three-way switching, under a very light load !

    Yukio YANO
     
  12. Eeyore

    Eeyore Guest

    In order to do that it must be getting power from somewhere. You must have a
    fault in the switch or related wiring.

    Graham
     
  13. Eeyore

    Eeyore Guest

    That would appear to be the case.

    Graham
     
  14. Eeyore

    Eeyore Guest

    How is this voltage induced ? Are you suggesting electromagnetic coupling ? That
    sounds astonishingly unlikely.

    Graham
     
  15. Ron(UK)

    Ron(UK) Guest

    If the neutral wire isn't properly grounded enough voltage can be
    induced by or leak from other 'live' circuits, maybe enough to cause the
    fluorescent fittings to randomly flicker. It could be a faulty switch
    leaking across the contacts.

    You don't live beneath an electricity pylon do you? It might also be
    the rays from guvmint mind control experiments entering your house. ;)

    Ron(UK)
     
  16. PeterD

    PeterD Guest

    Your switches are wired wrong (they are switching the neutral (or
    cold) side of the line, not the hot side. As well, you seem to have a
    leakage problem in the circuit as well. This leakage could be a switch
    or some other device or part.

    First step is to make 100% sure the switches are in the hot side of
    the circuit. That will likely solve your problem immediately. I'd
    guess there is a chance much of your house is not wired correctly from
    your description...

    Not sure what building codes/wriing codes you have in the UK, but in
    the US this circuit would not have passed a building inspector.
     
  17. Eeyore

    Eeyore Guest

    Ron, when the switch is off, there is no circuit. The neutral potential
    literally doesn't matter.

    Graham
     
  18. Eeyore

    Eeyore Guest

    Makes no difference. When the switch is off, the circuit is broken.

    Graham
     
  19. Meat Plow

    Meat Plow Guest


    Could you fix your news reader so it correctly quotes and attributes the
    previous post?
     
  20. Sjouke Burry

    Sjouke Burry Guest

    Capacitive leakage from the HOT wire to the switch
    wire? That could trickle charge and cause an
    occasional flicker.
    Random spikes would leak through much easier, and
    cause random flicker.
    Try as cure a small capacitor (100NF)across the
    lamp terminals, just as long as the cap is much
    bigger than the parasite one.
     
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