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Chinese "nightlight" !!

Discussion in 'Lighting' started by Ioannis, Aug 26, 2005.

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  1. Ioannis

    Ioannis Guest

    My mother bought this at a supermarket. It's a "nightlight" that plugs
    directly against a wall outlet.

    It has no country markings, just "1W", "AC220", "50/60Hz and "CE".
    The "CE" is probably bogus. It is probably of Chinese origin.
    http://users.forthnet.gr/ath/jgal/nitelite1.jpg

    I opened it and it contains a small low pressure mercury lamp, which
    contains 3 electrodes on each end. I suspect the third electrode is an
    auxiliary one, to initiate the discharge. You can discern the switch and the
    integrated circuit which plugs directly on the wall outlet.
    http://users.forthnet.gr/ath/jgal/nitelite2.jpg

    It's also problematic: Although it starts nicely and its glow looks like
    that of a miniature fluorescent the first 3-4 seconds, after 4-5 seconds,
    the auxiliary electrodes kick in again and it produces a purple glow around
    the electrodes which flickers on and off, similar to the starting argon glow
    on the discharge tube of a high pressure lamp.

    This leads me to believe that the circuitry is all faulty. It's probably
    supposed to be cutting off the current to the auxiliary electrodes, but
    instead the current through them continues, causing auxiliary discharges
    which keep going and going, causing argon flicker.

    Here's a picture of it being lit:
    http://users.forthnet.gr/ath/jgal/nitelite3.jpg

    The auxiliary discharges don't show on this pic.

    I was wondering how safe this thingy is. My impression is that leaving this
    thing unattended through the night, one risks the danger of fire. Opinions?
     
  2. Have you no faith in mankind? :)

    I don't see enough detail in the picture you posted. It
    looks like there are connections the lamp in three places,
    instead of three electrodes: each end plus the middle. It
    also look like there may be more than one wire going to each
    end. Can you post a more detailed photo or explain the
    connections bit more completely?

    Must be safe - it has the CE label. :)

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  3. JB

    JB Guest


    One of our chinese suppliers sent over a batch of floodlights for
    evaluation. I noticed that they had no CE marking so I called them up and
    explained.
    Two days later an envelope arrived containing a roll of 1000 CE stickers
    with a note: "Very sorry, forgot labels. Please stick onto fittings
    supplied. You all fully approved now!"
    You just got to love 'em.

    JB
     
  4. Ioannis

    Ioannis Guest

    No :)
    Here are two more detailed close-up photos:
    http://users.forthnet.gr/ath/jgal/nitelite4.jpg
    http://users.forthnet.gr/ath/jgal/nitelite5.jpg
    No. The middle thingy is the evacuation bubble. It doesn't show well on the
    previous photos. There's no wire connection there.
    Both ends have 3 contacts. Can you see the 3 wires on each end? I looked
    really close at them through the uncoated windows and two of them end up on
    the tungsten loop, while the third one terminates after entry to the tube.
    That's probably the auxiliary electrode.

    [snip]
     
  5. JohnR66

    JohnR66 Guest

    It was not the same as yours, but I had one similar. I opened it and traced
    the circuit. Some people doubled my accuracy, but I checked and diagram
    seems right. I don't understand the function of the scr.
    http://home.att.net/~jriegle/flor.jpg
    John
     
  6. Ioannis

    Ioannis Guest

    yes, that looks like the circuit, although I haven't checked it. The
    auxiliary ends make me believe that it's probably identical.
     
  7. Nice diagram. Due to the short across the electrodes, there
    is no way to heat the electrodes so the lamp must be stared
    in instant start mode. Since there is no source of high
    voltage, the "probe" electrode, attached to the "third" lead
    at each end is used to form a small discharge between the
    probe and the coiled electrode. Until the lamp starts, the
    full peak line voltage appears between the small probe
    electrode and the adjacent electrode and this is enough to
    initiate a discharge even with cold electrodes. The 10K
    resistors serve as the ballast for these small discharges.
    There is no switch to specifically shut down the auxiliary
    discharges, but the current should be less than 10 ma RMS.

    The SCR seems to cycle the lamp off on a regular basis by
    shorting it out. Are you sure that is an SCR and not a
    Triac, that will conduct in both directions?

    Based on some simple calculations, and an assumption that
    the lamp operating voltage is 30 volts and the Triac trigger
    voltage is 3 volts, the Triac will trigger about 3 msec
    after the start of each half cycle. Seems rather strange and
    perhaps I am wrong.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  8. Ioannis

    Ioannis Guest

    I left the light on for about 3-4 hours and the auxiliary Argon discharges
    on both ends dissappear in about 15-20 minutes after ignition and the lamp
    stabilizes to the color of a miniature fluorescent lamp.

    So there does not seem to be anything wrong with the circuitry. It does
    flicker very strongly, though. The flicker is noticeable using direct
    vision. Otherwise its spectrum is around that of regular daylight
    fluorescents and the residual phosphorescent light between light cycles has
    the same yellow-brown color as that of daylight fluorescents.
    What's an "SCR"?
    Perhaps I should test it by connecting it to the probes of my 125 Amp
    welding machine as well, to see if the "CE" sticker is valid :)
     
  9. The flicker may be caused by the Triac shorting out the lamp
    - perhaps to reduce the energy consumption.
    Silicon Controlled Rectifier. The forerunner of the Triac.
    It's like a Triac but carries current in only one direction.
    Before you do that can you take a look at the lamp current
    waveform or the light output waveform to see if it is being
    shut down each cycle about midway through?

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  10. Ioannis

    Ioannis Guest

    Ï "Victor Roberts" <> Ýãñáøå óôï ìÞíõìá
    [snip]
    Sorry, I don't have the equipment to do this. The best I can do is compare
    its strobo frequency to that of a normal fluorescent by direct eye
    inspection. I'll try that later tonight if I have time.
     
  11. Ioannis

    Ioannis Guest

    Nobody answered by question yet: How safe is this thingy left unattended at
    night?

    Two years ago, I by mistake left a "CE" marked Chinese tabletop 9W
    fluorescent on, only to return after a week to find the entire fixture
    melted. Everything. Lamp, transformer housing and wiring. Any chance of this
    happening here?

    Also, does anybody know anything about life expectancy for this thing?
     
  12. I don't think anyone of us has enough information to answer
    this question.
    Did you ever figure out why this other lamp melted?
    This would require life tests to be conducted on more than
    one sample. Unless someone has access to such life test data
    or has more than 10 of these in their own homes, I don't see
    how personal experience or a guess will give an accurate
    answer.

    If you are not comfortable with it, then you should not use
    it.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  13. Ioannis

    Ioannis Guest

    In the beginning the tabletop was operating fine and I could detect a
    certain temp on the ballast housing. When I came back after this one week,
    the ballast housing was a lot hotter and melted. The primamry cause seems to
    have been either a ballast meltdown or some other reason which caused the
    overheating of the ballast. The wiring and lamp simply followed suit.

    What exactly can cause a fluorescent ballast to meltdown?

    Thanks.

    [snip]
     
  14. I've lost track of the design features of this other lamp.
    If it has an inductive ballast, it is always possible for a
    turn-to-turn short to develop, but those are unusual. If the
    output of an inductive ballast becomes shorted, it will draw
    more current than when it is operating a lamp and that could
    cause overheating.

    The circuit we were discussing earlier in this thread uses a
    capacitor ballast if I remember correctly. It is possible
    for a capacitor to develop an internal short, but that is
    unlikely with a new capacitor. If the output of the
    capacitor ballast is shorted the capacitor should not
    overheat.

    There were also a few resistors in the power circuit posted.
    Any of them could have overheated.

    The problem with low cost electronics is often not the
    components but the construction. Poor solder joints that can
    overheat, thin circuit board traces that can overheat, or
    traces placed too close to each other on the circuit board
    that can cause flash-over shorts which can cause other parts
    to overheat.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  15. Ioannis

    Ioannis Guest

    Ï "Victor Roberts" <> Ýãñáøå óôï ìÞíõìá
    [snip]
    Ok, thanks. But on the circuit we are discussing, this is still a low
    pressure mercury vapor lamp, which still has a negative resistance
    characteristic. So, if, just if, for some obscure reason, the circuit gets
    mangled (due to a short or some other reason) and the lamp faces the full
    voltage of the wall outlet (because of a short in the circuit), then it will
    probably blow up.

    This particular tube has no safety molybdenum end seals which could prevent
    the more dire consequences of a direct short, so giving it a 220V
    unrestricted, will most likely cause it to "flash" causing its end points to
    at least melt in the best possible case, or explode in the worst possible
    case.

    Am I not right?
     
  16. I have never heard of a fluorescent lamp exploding. The gas
    pressure is just too low.

    If you operate a fluorescent lamp without a proper ballast
    the first thing that will happen is that the electrodes will
    be destroyed. This ruins the lamp but causes no damage
    outside the lamp.

    If you have enough voltage to keep the discharge operating
    with only the electrode support leads, and this happens
    quite often in the US on instant start circuits and could
    happen with your short lamp, especially on 220 volts, then
    the ends of the lamp will overheat, which will often cause
    the glass to crack, allowing air inside the lamp, which
    extinguishes the discharge. If the lamp is a pin-base CFL
    with the lamp ends surrounded by a plastic base, that base
    can melt and under some circumstances can start a fire. If
    the lamp is a linear instant start lamp, when the glass
    cracks the lamp can fall out of the fixture and damage
    property located below or injure a person who may be seated
    or standing below the fixture.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  17. JohnR66

    JohnR66 Guest

    Vic, I googled BT169D and it found a PDF datasheet. It is a passivated,
    sensitive gate SCR. The way it is wired, it seems to be activated by a
    voltage across the ballast components, perhaps during starting. Why an SCR?
    not sure. Creating asymetrical waveform condition?
    John
     
  18. OK - new theory of operation :)

    First of all, my previous explanation assumed that the gate
    was connected to the lamp side of the capacitor ballast,
    which is incorrect. The gate is connected across the line,
    except for the parallel 390 ohm resistors which can't drop
    much voltage when the lamp is operating. And, as you say,
    it's an SCR.

    Before the lamp starts, the SCR will be triggered during the
    cycle when the right hand power lead is positive with
    respect to the left lead. This will quickly charge the 1uF
    capacitor to just about peak line voltage with its left lead
    positive with respect to the right lead, with the charging
    current spike being limited only by the series resistance of
    SCR and the two parallel 390 ohm resistors - 195 ohms.

    The discharge time constant of the 1 uF capacitor and the 1
    meg resistor is 1 sec, so the capacitor will remain almost
    fully charged when the line polarity reverses a few msec
    later. When the right hand input terminal becomes negative,
    the voltage on the capacitor adds to the line voltage,
    providing twice the peak line voltage across the lamp to
    start it.

    However, what I can't figure out at this late hour is what
    makes the SCR stop triggering each cycle. If it continues
    triggering each cycle, then the lamp will be operating for
    one full half cycle and only a part of the other half cycle,
    leading to significant flicker.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  19. I would think shorting of turns of wire in the winding in the ballast.

    This could result from two events that I could think of:

    1. The design was marginal and sooner or later this was likely to occur.

    2. The lamp fails, and a glow switch starter gets stuck shorted after a
    enough thousands of blinks. The ballast is supposed to survive this,
    but I have seen how this led to a fire in the elevator in an apartment
    building that I was living in several years ago.

    If you know the beand and model of the ballast (or fixture), and any
    numbers on the certification sticker, you should report all such info to
    the agency that supposedly certified the ballast (or fixture).
    If the certification is in any way invalid, I wonder if whoever is
    falsely applying certification stickers is hoping that any resulting fires
    burn up names/numbers to use against the offenders.

    - Don Klipstein ()
     
  20. I think that the lamp will survive faults well enough to force faulty
    ballasts to act as fuses unless the short is severe enough to blow an
    actual fuse or trip a breaker.
    And if the fault causes the lamp current to be a few times what it
    should be, I expect that in many cases the lamp will survive long enough
    to cause the malfunctioning ballast to overheat enough to further fail and
    maybe do so quite spectacularly (and possibly pouring or spitting drops of
    molten copper, of temperature a little under 1100 degrees C).
    High pressure sodium may usually be either more forgiving or drag things
    out farther, by having an overpowered lamp vaporize excessive sodium, and
    once the arc voltage reaches about 76-80% or so of the ballast output open
    circuit voltage, the "negative resistance" of the arc typically outweighs
    the output impedance of the ballast in some way to make the arc unstable
    upon decrease of current - and the next downward fluctuation of arc
    current during the next half-cycle puts the arc in a decreasing-current
    tailspin, and the lamp goes out. You get something similar to
    "end-of-life cycling", only you hope the lamp spends enough time being
    "off" or gets worse fast enough to not let the ballast overheat enough to
    make things worse.
    I think that some few ballast failures resulting in lamp current a few
    times that of "normal" could result in lamp current that does not make the
    lamp "act as a fuse", but merely ages the lamp badly, and the lamp may
    "keep on ticking" long enough for the ballast to get worse - and maybe in
    especially bad cases put on a fireworks show or put out molten copper.
    I do admit that this is an extreme case, but falling a little short of
    this is still an obvious fire hazard. If the ballast windings overheat
    enough to produce a flammable concentration of vapors of insulating
    materials and then a wire shorts or breaks with a spark, at that point you
    could have a fire. This is still a very rare event, but this is something
    that I think should be planned around (for adequate avoidance and/or
    survival) in order to receive a UL or CSA or CE sticker.

    - Don Klipstein ()
     
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