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  1. #1
    Marco Gilardetti's Avatar
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    Durst Laborator; problems with EST 450 unit.

    Good morning everybody.

    Unfortunately my Durst Laborator is having bad problems. It burned out three replacement lamps in few minutes. I suppose the problem lays with the power supply unit EST 450, probably the stabiliser isn't working properly.

    The very strange thing is, however, that the lamps seem to be UNDERpowered. When I replaced them, everything seemed all right, perhaps just a bit too dim, at the beginning, but within a minute or so the light began getting dimmer and dimmer until the lamp failed and showed a glass all covered by a grey-black powder. Also, I measured the voltage fed to the lamp with a high quality tester and, without load, it read 21 Volts AC rather than the expected 24.

    Does anyone know if these 24V 250W halogen lamps can fail for undervoltage? Perhaps by poisoning the gas inside the glass bulb, or by ionisation or such? It's such a strange thing.

    Also, does anyone experimented something similar and can guess which component inside the power supply can be faulty? It's quite a complicated circuit, very hard to figure out, but none of the components shows obvious traces of damage.

    The head fan is working properly, so I would exclude a problem with overheating. Lamp failure also happens too fast to be due to overheating inside the head.

    Thanks to anyone who will help to find out what the problem is.
    I know a chap who does excellent portraits. The chap is a camera.
    (Tristan Tzara, 1922)

  2. #2
    Marco B's Avatar
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    According to one site I saw referencing the required ELC 24V/250W lamps, the official life-time of these bulbs is just 50(!) hours. Probably not a big deal for an enlarger switching on just seconds each time used, but it might explain why lamps may fail almost instantly like in your case if the power supply has a problem. These lamps seem to be pushed to the limits in usage.

    I doubt if "under-voltage" could be an issue. It is a halogen lamp, which is equivalent to a incandescent lamp with a hot metal filament producing the light. The halogen lamp contains an inert gas, which can't react chemically with anything. It is the filament which "burned" up in those minutes, causing the apparent "soot" on the inside of the bulb.

    Gas discharge lamps, like a fluorescent energy saving lamp, could have issues with changes in voltages, as they need to maintain an "arc" of excited gas ions (think of a kind of controlled thunder lightning - the arc produces the light!) in the gas discharge tube, leading to a possible premature death of the lamp in cases with power issues.
    Last edited by Marco B; 02-07-2011 at 03:46 AM. Click to view previous post history.
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  3. #3

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    Rüdiger Mehlmann

    have you tried asking Mr. Mehlmann.


    Mehlmann Fototechnik
    --- autorisierter Durst Kundendienst ----
    Schillerstr. 9a
    D 74889 Sinsheim
    RMehlmann@durst-image.de

    Telf. +49 (0) 7261 17506
    Mobil +49 (0) 172 6313316

    he was very helpful with a problem I had.

    best

  4. #4

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    Hello !
    Halogen bulbs can die from undervoltage/power. This is due to the fact that the tungsten filament vaporize in normal use (slowly, I have to admit) and deposit itself on the quartz envelope of the bulb. The halogen inside the bulb react with the deposited tungsten and return it to the filament. This occurs only at the specified temperature of the filament which is greatly impacted by the voltage the lamp gets. this improve bulb life expectancy and output quality (as the bulb does not get covered with a thin layer of non transparent metal with age).
    As these bulbs are quite expensive, I would test run the power supply with a resistor in place of the bulb (a household iron or something like that comes to mind) because the stabilization process needs to supply the correct voltage and power to work.
    In other words, measuring the voltage without load is irrelevant as the regulation is not meant to work so could be dead and your meter not seeing it. If you force the current to reach the value the lamps normally draws you will see if the regulation works fine or is dead/havoc.
    I do not know this particular circuit but these devices normally limit the power and regulate it at the 250 W specified and, of course, at the nominal voltage to prevent color temperature change in the bulb's output.
    Bear in mind that this electronics is from the seventies and could be impossible to repair due to the lack of components which can be obsolete... So do not make destructive testing ....

  5. #5
    Marco B's Avatar
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    Quote Originally Posted by GeorgesGiralt View Post
    Hello !
    Halogen bulbs can die from undervoltage/power. This is due to the fact that the tungsten filament vaporize in normal use (slowly, I have to admit) and deposit itself on the quartz envelope of the bulb. The halogen inside the bulb react with the deposited tungsten and return it to the filament. This occurs only at the specified temperature of the filament which is greatly impacted by the voltage the lamp gets. this improve bulb life expectancy and output quality (as the bulb does not get covered with a thin layer of non transparent metal with age).
    I knew about the re-deposition of tungsten back on the filament in halogen, but never realized it was so much influenced by the temperature of the lamp, as you always see dimmers on halogen units. I never realized they would actually potentially negatively affect lamp life.

    Ah well, I now see that Wikipedia states:

    "Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage. However the light output is reported as proportional to V3, and the efficacy proportional to V1.3.[13] The normal relationship regarding the lifetime is that it is proportional to V − 14. For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the efficacy would be about 6.5% higher, but would be expected to have only half the rated life."

    So it seems lower voltage still expands life expectancy of most halogen bulbs... but it depends, another page says this:

    "Will dimming my halogen bulb extend it's life?

    The halogen cycle can be interrupted if the voltage and temperature of the lamp is operated too low. The result is lamp blackening. Lamp blackening and the consequent loss of lumens are standard for incandescent lamps, but halogen lamps are designed not to blacken as they age. Halogen lamps maintain their lumen output throughout their lifetime due to the key mechanism of the halogen cycle which binds with the tungsten that is vaporized off of the lamp filament itself. Thus keeping the bulb walls clean. If lamp engineers could figure a way to get the tungsten to redeposit evenly back on the lamp filament, we could have a lamp that lasts forever. But, this is not the case, as the tungsten is redeposited on the coolest part of the filament (usually the ends of the filament), and consequently over time, the middle portion of the filament eventually thins, forming a weak spot, and eventually the filament breaks.
    The standard operating temperature of the bulb wall to maintain a halogen cycle is 250C. When the temperature falls below this level the halogen cycle fails, and the lamp starts to act like a standard incandescent. It is estimated that the cycle fails when a lamp is operated below 70-80% of its rated power."


    So, at some reduced voltage, you probably do get reduced life span, as the halogen cycle breaks down.
    Last edited by Marco B; 02-07-2011 at 10:03 AM. Click to view previous post history.
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    "Analog is chemistry + physics, digital is physics + math, which ones did you like most?"

  6. #6
    Marco B's Avatar
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    And another nice page on this subject of halogen cycle is:

    Halogen Regenerative Cycle:
    http://zeiss-campus.magnet.fsu.edu/t...cle/index.html

    Marco
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    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "I don't know, maybe we should disinvent color, and we could just shoot Black & White." - David Burnett in 1978

    "Analog is chemistry + physics, digital is physics + math, which ones did you like most?"

  7. #7

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    Measuring the voltage without a bulb in place may be an indication of a problem. Some stabilizer circuits don't work very well without a load and will hold the voltage below normal.

    Check for loose wires, poor contacts, including the bulb socket itself. The socket should almost be replaced when you change a bulb, as the spring contacts inside it go thru many heat cool/cycles in an enlarger and that weakens the springs.

    Good bulbs don't fail in a couple of minutes from running 10-15% under voltage, they will last for days. Sounds like all your spare bulbs came from the same batch and were all bad to start with, possibly due to damage in shipping. I would try to return them for a refund.

  8. #8
    ic-racer's Avatar
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    1)None of the TRA450 schematics I am aware of show a stabilization circuit. Basically its just a 24v transformer and some additional 'housekeeping' circuitry.
    2) Under voltage will not cause that bulb to blow. As an example I ran the 18 V EKG bulb from an enlarger off a half-wave rectified 13V circuit for 20 years with no problem.
    3) Bob-D659 gives good advice on the socket. I have taken the rivets out of sockets and taken them apart to restore the contacts but new sockets ARE available if you look around. The names/numbers of the sockets don't always match the bulb. For example the socket for the Omega D5500 is called QLV-1 but the bulb is a MR-16 style.

  9. #9
    Marco B's Avatar
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    Quote Originally Posted by ic-racer View Post
    2) Under voltage will not cause that bulb to blow. As an example I ran the 18 V EKG bulb from an enlarger off a half-wave rectified 13V circuit for 20 years with no problem.
    Yes, I guess we wouldn't be running all those nice halogen dimmed lighting options in houses otherwise, if they broke down each time you lowered the light output to prepare for a cosy evening with your peer. Still, that concept of the halogen cycle and its chemistry is nice to learn about

    Quote Originally Posted by ic-racer View Post
    3) Bob-D659 gives good advice on the socket. I have taken the rivets out of sockets and taken them apart to restore the contacts but new sockets ARE available if you look around. The names/numbers of the sockets don't always match the bulb. For example the socket for the Omega D5500 is called QLV-1 but the bulb is a MR-16 style.
    Is it than because the socket due to repeated heating/cooling cycle, simply no longer makes proper contact, and causes unwanted arcing / charges to jump over to the lamp contacts, resulting in some form of damage? What is the cause of the failure of the lamps in this case? Shouldn't one see clearly irregular lighting in this case and is it consistent with the description of the way of failure the OP desribed?:

    "The very strange thing is, however, that the lamps seem to be UNDERpowered. When I replaced them, everything seemed all right, perhaps just a bit too dim, at the beginning, but within a minute or so the light began getting dimmer and dimmer until the lamp failed and showed a glass all covered by a grey-black powder. Also, I measured the voltage fed to the lamp with a high quality tester and, without load, it read 21 Volts AC rather than the expected 24."

    Or is there still the option of some power supply issue?

    Marco
    My website

    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "I don't know, maybe we should disinvent color, and we could just shoot Black & White." - David Burnett in 1978

    "Analog is chemistry + physics, digital is physics + math, which ones did you like most?"

  10. #10
    36cm2's Avatar
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    Quote Originally Posted by ic-racer View Post
    1)Basically its just a 24v transformer and some additional 'housekeeping' circuitry.
    Not to hijack the thread, but I believe my Durst L1200 stabiliser was fried last week due to a power surge. Does this mean I can just replace it with a generic 24v transformer, or am I oversimplifying?

    Thanks,
    Leo
    "There is a time and place for all things, the difficulty is to use them only in their proper time and places." -- Robert Henri

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