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CFL ballast design, and using dead lamps for repair

Discussion in 'Electronic Repair' started by P E Schoen, Jan 21, 2013.

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  1. P E Schoen

    P E Schoen Guest

    I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent bulb,
    that I use constantly for working on PCBs and electronics projects in
    general. I bought it several years ago and recently it started flickering
    and then died. I replaced the bulb, but still no joy, and after replacing
    the blown fuse and two damaged transistors, I found that the little
    transformer had an open winding.

    So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
    little circuit in them should work. I had a couple of broken or dead bulbs
    ready for recycling, so I opened the bases, cut the leads, and extracted the
    PCBs. After a few unsuccessful tries, I was able to get it to work and now
    my lamp is once again operational.

    I found some schematics of the CFL driver boards here:
    http://www.pavouk.org/hw/lamp/en_index.html

    Some of those circuits matched what I had almost exactly. It was a little
    difficult to follow the explanation of how they operate, but what was
    confusing is the four pins shown on the lamp itself, which is also how the
    bulbs are made. I assume they are the heaters that are usually activated
    with a starter, but I did not find any continuity on those pins. The desk
    lamp only had one wire to each of two pins on the circline bulb, but in the
    CFLs all four wires were connected to different points on the PCB. It would
    only work when I shorted the connections that would have gone to the
    heaters, and it seems to work very well. It starts to light at 50 VAC and
    reaches full brightness at 100-120V, at which it draws about 100mA. That's
    close enough to 12 watts for me!

    Here's a little clip of my repair project:


    This is good to know. Those little circuits in each CFL have a lot of good
    components, including a DIAC and high voltage transistors, and it's probably
    possible to use them to drive small fluorescent lamps for DIY projects or
    repair. I doubt they could be used for the 40W tubes, but a driver from a
    100W CFL should work on a 20W tube such as are in many desk lamps and small
    kitchen fixtures.

    Does anyone know if there is any problem with this?

    Thanks,

    Paul

    PS: GO RAVENS!!!!!
     
  2. N_Cook

    N_Cook Guest

    I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent bulb,
    that I use constantly for working on PCBs and electronics projects in
    general. I bought it several years ago and recently it started flickering
    and then died. I replaced the bulb, but still no joy, and after replacing
    the blown fuse and two damaged transistors, I found that the little
    transformer had an open winding.

    So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
    little circuit in them should work. I had a couple of broken or dead bulbs
    ready for recycling, so I opened the bases, cut the leads, and extracted the
    PCBs. After a few unsuccessful tries, I was able to get it to work and now
    my lamp is once again operational.

    I found some schematics of the CFL driver boards here:
    http://www.pavouk.org/hw/lamp/en_index.html

    Some of those circuits matched what I had almost exactly. It was a little
    difficult to follow the explanation of how they operate, but what was
    confusing is the four pins shown on the lamp itself, which is also how the
    bulbs are made. I assume they are the heaters that are usually activated
    with a starter, but I did not find any continuity on those pins. The desk
    lamp only had one wire to each of two pins on the circline bulb, but in the
    CFLs all four wires were connected to different points on the PCB. It would
    only work when I shorted the connections that would have gone to the
    heaters, and it seems to work very well. It starts to light at 50 VAC and
    reaches full brightness at 100-120V, at which it draws about 100mA. That's
    close enough to 12 watts for me!

    Here's a little clip of my repair project:


    This is good to know. Those little circuits in each CFL have a lot of good
    components, including a DIAC and high voltage transistors, and it's probably
    possible to use them to drive small fluorescent lamps for DIY projects or
    repair. I doubt they could be used for the 40W tubes, but a driver from a
    100W CFL should work on a 20W tube such as are in many desk lamps and small
    kitchen fixtures.

    Does anyone know if there is any problem with this?

    Thanks,

    Paul

    PS: GO RAVENS!!!!!


    +++++++++

    so the original lamp was conventional ballast and 2 pin bimetal switch
    starter ?
     
  3. Tim Williams

    Tim Williams Guest

    Besides the electrolytic and bulb, the starter cap is very failure-prone.
    In circuits where the filaments are used, it's in series with the output,
    forming a series resonant tank; the low resistance of the cold filaments
    draws lots of current, starting the tube quickly. When the tube starts
    up, it appears in parallel with the cap, transforming the circuit into a
    good old series inductance ballast.

    The kind with only two pins skips the heating step and allows the tank
    voltage and current to resonate even higher, until the tube breaks down
    cold-cathode style. Once ignited, ion bombardment keeps the filaments
    warm, keeping the reignition and operating voltages normal.

    High voltage film caps are big and expensive, so understandably, they
    don't like to use them very much. Often, a poor green (polyester) type is
    found, which isn't even green anymore, but black from the abuse. Others
    may be burned through, having experienced too many starts (too much peak
    voltage) that self-healing has burned away most of the capacitance. The
    circuit then either tries oscillating too high (burning itself from
    switching loss) or oscillates lazily or latches (resonance no longer
    strong enough to draw enough current to provide sufficient feedback).

    Tim

    --
    Deep Friar: a very philosophical monk.
    Website: http://seventransistorlabs.com

    I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent
    bulb,
    that I use constantly for working on PCBs and electronics projects in
    general. I bought it several years ago and recently it started flickering
    and then died. I replaced the bulb, but still no joy, and after replacing
    the blown fuse and two damaged transistors, I found that the little
    transformer had an open winding.

    So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
    little circuit in them should work. I had a couple of broken or dead bulbs
    ready for recycling, so I opened the bases, cut the leads, and extracted
    the
    PCBs. After a few unsuccessful tries, I was able to get it to work and now
    my lamp is once again operational.

    I found some schematics of the CFL driver boards here:
    http://www.pavouk.org/hw/lamp/en_index.html

    Some of those circuits matched what I had almost exactly. It was a little
    difficult to follow the explanation of how they operate, but what was
    confusing is the four pins shown on the lamp itself, which is also how the
    bulbs are made. I assume they are the heaters that are usually activated
    with a starter, but I did not find any continuity on those pins. The desk
    lamp only had one wire to each of two pins on the circline bulb, but in
    the
    CFLs all four wires were connected to different points on the PCB. It
    would
    only work when I shorted the connections that would have gone to the
    heaters, and it seems to work very well. It starts to light at 50 VAC and
    reaches full brightness at 100-120V, at which it draws about 100mA. That's
    close enough to 12 watts for me!

    Here's a little clip of my repair project:


    This is good to know. Those little circuits in each CFL have a lot of good
    components, including a DIAC and high voltage transistors, and it's
    probably
    possible to use them to drive small fluorescent lamps for DIY projects or
    repair. I doubt they could be used for the 40W tubes, but a driver from a
    100W CFL should work on a 20W tube such as are in many desk lamps and
    small
    kitchen fixtures.

    Does anyone know if there is any problem with this?

    Thanks,

    Paul

    PS: GO RAVENS!!!!!
     
  4. "P E Schoen" <> schreef in bericht
    I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent bulb,
    that I use constantly for working on PCBs and electronics projects in
    general. I bought it several years ago and recently it started flickering
    and then died. I replaced the bulb, but still no joy, and after replacing
    the blown fuse and two damaged transistors, I found that the little
    transformer had an open winding.

    So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
    little circuit in them should work. I had a couple of broken or dead bulbs
    ready for recycling, so I opened the bases, cut the leads, and extracted the
    PCBs. After a few unsuccessful tries, I was able to get it to work and now
    my lamp is once again operational.

    I found some schematics of the CFL driver boards here:
    http://www.pavouk.org/hw/lamp/en_index.html

    Some of those circuits matched what I had almost exactly. It was a little
    difficult to follow the explanation of how they operate, but what was
    confusing is the four pins shown on the lamp itself, which is also how the
    bulbs are made. I assume they are the heaters that are usually activated
    with a starter, but I did not find any continuity on those pins. The desk
    lamp only had one wire to each of two pins on the circline bulb, but in the
    CFLs all four wires were connected to different points on the PCB. It would
    only work when I shorted the connections that would have gone to the
    heaters, and it seems to work very well. It starts to light at 50 VAC and
    reaches full brightness at 100-120V, at which it draws about 100mA. That's
    close enough to 12 watts for me!

    Here's a little clip of my repair project:


    This is good to know. Those little circuits in each CFL have a lot of good
    components, including a DIAC and high voltage transistors, and it's probably
    possible to use them to drive small fluorescent lamps for DIY projects or
    repair. I doubt they could be used for the 40W tubes, but a driver from a
    100W CFL should work on a 20W tube such as are in many desk lamps and small
    kitchen fixtures.

    Does anyone know if there is any problem with this?

    Thanks,

    Paul

    PS: GO RAVENS!!!!!

    The traditional way of igniting TLs is first heating the heaters and then
    start it with a relative high voltage puls. But heating first is not
    necessary. The lamp will ignite if only the voltage of the ignition pulse is
    high enough. Nevertheless, the heaters cannot be omitted as they provide the
    electrons required for the current through the tube. Especially low power
    TLs are sometimes ignited this way. When used with low frequencies i.e. 50Hz
    or 60Hz, it is said to shorten the lifetime of the tube. The circuit I ever
    found in a handheld 8W TL lamp did work but gave a flickering light.

    I also use a magnifier lamp but a bigger one containing a 22W circline. It
    came with an old-fashioned iron ballast and no starter. I had to start it
    by hand using the special switch. That is I had to push the button and keep
    it pushed for a 6s. During this time the heaters were on. Relieving the
    button ignited the lamp... Most of the times. But over time igniting failed
    more and more and the circlines seemed to worn out faster and faster.
    Investigating revealed the special switch to be worn out beyond repair. So I
    got a 20W CFL, got out the electronics, put them in a box and connected it
    to the circline. Works fine for several years now already.

    petrus bitbyter
     
  5. Phil Allison

    Phil Allison Guest

    "P E Schoen"

    It starts to light at 50 VAC and
    reaches full brightness at 100-120V, at which it draws about 100mA. That's
    close enough to 12 watts for me!


    ** You are mixing up "watts" and "VA".

    CFL inverters, like most simple SMPS, have a PF of about 0.6 due to the
    peaky current wave shape drawn from the AC supply - so VA and watts
    numbers differ by about a 2:1 ratio.

    You did use a wide band "true rms " meter to measure the AC current -
    didn't you ?



    .... Phil
     
  6. Guest

    FWIW, of the modest pile of CFLs I autopsied from my own house, 100%
    of the failures were from failed heaters.

    This may be atypical. I get good service from CFLs running them
    without enclosures; the enclosed, base-up fail modes may be different.
     
  7. Tim Williams

    Tim Williams Guest

    of the failures were from failed heaters.
    without enclosures; the enclosed, base-up fail modes may be different.

    I don't know if any do fail specifically due to the start cap -- as you
    note, the filament tends to fail first. I haven't measured any of the
    caps to see the capacitance loss, but the color change is reason enough.

    EPCOS makes capacitors specifically for this service; their graphs of peak
    voltage vs. capacitance are reminiscient of the Write-Only Memory's
    "insertions vs. pins remaining" graph. ;-o

    Base-up tends to cook the capacitor; better ones don't mind so much. My
    parents have a GE "long life" model on their front porch, an enclosed
    (vented enough that bugs find their way in, but not so much that they find
    their way out before dying and making a pile...), base-up fixture.

    I installed them something like four years ago; the other outdoor lights
    (upright, even) have since failed, but the front porch, surprisingly,
    still works.

    I think. Come to think of it, I didn't look closely last time I was by;
    the front porch may've been replaced, most likely under pressure, the
    other "low priority targets" simply being "left in the dark"... :)

    Tim
     
  8. P E Schoen

    P E Schoen Guest

    wrote in message
    I measured the heaters on one of the new circline lamps and they appear to
    be about 3 ohms each. So in series, using a starter, they would draw a high
    current surge and then probably much lower as they become nearly
    incandescent. Of course the ballast would limit the current to some much
    lower value. I figure that an ordinary magnetic ballast for 12W would drop
    about 30 volts at 100 mA during normal operation, so probably about 400 mA
    into the heaters.

    But since this lamp had only two wire zipcord going from the electronic
    ballast to the lamp, it obviously did not use the heaters with the original
    circuit. So I just shorted the connections for the heaters at the board, and
    it works perfectly well. I can't see where the 6 ohms of filament resistance
    would make much difference to a circuit designed for 100 mA, and I don't
    know why the CFLs use the heaters at all, or why they should burn out. It
    does appear that the heaters of the one dead CFL are open, although I
    thought I had continuity through one when I first measured it. One of the
    CFLs actually got broken when I hit it with a flyswatter as I waged war on
    the stinkbugs that love to circle the lamp. It seemed to continue to glow
    for a while, which may have been the heaters.

    The defunct circline lamp shows discoloration on one end and that heater is
    open, while the other is OK. I don't know how it can burn out if there is
    only one wire connected to it. Perhaps it just vaporizes because of the
    current flowing from it into the fluorescent plasma? I don't really know the
    details of operation.

    When I was still in High School I made a little multivibrator circuit that
    fed a 12V transformer and I connected the 120V winding through a capacitor
    to a small fluorescent lamp in a camping lantern. It originally used a big
    high voltage battery (maybe 90 volts and maybe two of them), and maybe some
    sort of vibrator as in old tube type car radios to get the AC voltage for
    the lamp. Will it work on just DC? My conversion worked on a 12V motorcycle
    battery, and it was instant start, whereas the original had a starter
    button. I think I still have that lantern somewhere. I should find it and
    look inside.

    I also have an old lantern that originally used two big doorbell batteries
    (remember them?), and I replaced them with a NiCad battery that was made of
    plexiglass so you could see the plates and electrolyte inside and possibly
    even service it. My father worked for a company that made exotic batteries
    for the military and I think this came from there, probably 50 years ago.

    Paul
     
  9. In other words, used like this, they are not heaters but cathodes.
    Presumably this is what a 'cold cathode' tube is.
     

  10. Sure. During the classic startup you can consider the heaters to be direct
    heated cathodes. Once the light is on they are pretty hot cold cathodes :)

    petrus bitbyter
     
  11. Most CFLs have PTC thermistors that increase current flow
    Fortunately, I have not had this problem. The CFLs in my bathroom and bedroom
    have lasted two to three years, and are turned on and off several times a day.
     
  12. Guest

    Two or three years? I have incandescents that last a lot longer than
    that.
     
  13. Guest

    Can lights aren't ventilated. In fact, many are insulated (IC rated).
    They're hell on CFLs.
     
  14. Phil Allison

    Phil Allison Guest

    "Ian Field" <
    ** See the second half of this page for pics of the actual CFL and fitting.

    http://sound.westhost.com/articles/il-cfl-6.htm

    The are no ventilation a holes at the back of the fitting and all the spiral
    CFLs were a neat fit.



    .... Phil
     
  15. legg

    legg Guest

    One other thing you can learn from this exercise - low cost part
    types.

    Typical gapped core sizes commonly used in this application can be
    designed in elsewhere for $0.02. Similar price ranges for bobbins,
    semiconductors, film caps, fuses and electrolytics.

    Lots of other things you can do with this stuff, knowing you won't be
    beat on material cost.

    RL
     
  16. I must be stupid then. I've got a CFL in a totally sealed (shower)
    fixture and it's been working fine for years. (I even conformally
    coated the lamp before sealing it in the fixture).

    I only buy name brand (eg. Philips) products though, and probably
    they're made a bit better than the ones that come 8 to a card. Never
    seen any perforation of the housings on failure.
     
  17. Parts that are marked the same are not necessarily the same. The $1.00
    bulbs may contain gold-colored caps marked as 630VDC/125°C.

    http://www.discovercircuits.com/dc-mag/Issue_4/Photos/FakeCapacitor1.jpg

    Not sure if the 240V input makes much difference.. they are likely
    using a doubler circuit in our (120V) lamps.

    I have heard enough stories of people who bought the cheap ones and
    had initial failures, exciting failures, and such like to avoid the
    low end stuff.

    It would be nice if LED lamps got anywhere close to the brightness of
    CFL, halogen or incandescent bulbs at a reasonable price, but they are
    not very close yet. Maybe in a few years. I bought a couple MR11
    "brightest on the market" bulbs to unload the halogen xfmr and allow
    me to put a bigger halogen in the centre bulb of a 3-light string, and
    they're not even comparable. I'll have to take some quantitative
    measurements at some point.
     
  18. Lumens per watt is probably okay. The problem is that they're using
    discrete SMT LEDs and the $ per incremental lumen is far more than for
    a CFL.

    These are the ones I bought.
    http://www.amazon.com/gp/product/B007DA05O6/ref=oh_details_o00_s00_i00

    I'd prefer to have 50W or 100W equivalent that burns 5 or 10W.
     
  19. Nice artcile Phil, But don't worry about the legislature's doing
    anything. What's needed is some lawayer to get a hold of it and sue
    the manufacturers.

    (That's the US way :^)

    George H.
     
  20. The offshore manufacturers are probably not easy to get substantial
    judgements against- but the stores, especially those who do their own
    importing, have deep pockets and can't easily escape.

    They do have a good defense though- if it has safety agency approval,
    it's presumed to be safe. Maybe report it to the safety agencies- but
    I don't see anthing there that would really raise the alarm-
    incadescents break and short internally and implode from time to time,
    and none of the burn- through incidents shows support of combustion.
    Any fixture designed for a normal incandescent ought not to burn the
    office or house down. The one that 'exploded' is the closest one- the
    mfr may have substituted a cheaper non-fiberglass sleeving on that
    diode.
     
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