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Xenon flashlight bulb bypass capacitor?

Discussion in 'Electronic Design' started by John Doe, Jan 29, 2005.

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  1. John Doe

    John Doe Guest

    This is my question:
    Can a bypass capacitor help increase the life of a xenon bulb? If so
    please tell me what general type of capacitor.

    If any regular here is familiar with xenon light bulbs, I'm sure this
    is a simple question for you.

    I just bought a light weight, extremely bright dual Xenon flashlight.
    Replacement bulbs are difficult to get. They will be switched on and
    off frequently.

    They look like medium to large size clear LEDs each with two short
    leads. I guess it's six volts per xenon bulb, I will multimeter
    voltage/current/resistance stuff if that might help.

    The work involved is no problem.

    Thank you.
  2. John Larkin

    John Larkin Guest

    Sorry, no.

  3. I read in that John Doe <.
    No. But a very low value series resistor would. However, it does reduce
    brightness. A more complicated inrush-current limiter would work, but
    again there would be a loss of brightness unless you use a relay (or
    maybe a selected power FET) to short-circuit a series resistor after a
    0.5 second delay.
  4. SioL

    SioL Guest

    Self-heating NTC resistor?

  5. John Doe

    John Doe Guest

    How about a coil?
  6. In theory, yes, but I don't know of any that would do the job for a low-
    voltage xenon lamp. Might be worth looking round.
  7. I read in that John Doe <.
    You mean using an inductor to limit the inrush? I doubt that it's
    practicable. The required L/R ratio is too high. I don't know what lamp
    you have or what a suitable inrush current limit is, but for a 6 V
    supply and a 6 V 1 A lamp, to limit the initial rate of change of
    current to 1 A/s, assuming zero cold resistance for the lamp, you need a
    6 H inductor. The resistance needs to be well below 0.6 ohm so as not to
    affect brightness. OK, the inductor can saturate when the full current
    is flowing, but that's still a sizeable inductor.
  8. SioL

    SioL Guest

    I've seen a similar solution offered for a regular 220V mains lamp,
    many many years ago (15+ years).
    Of course current is a lot smaller there so a few ohms might be tolerable,
    whereas for a xenon, probably not.

  9. Guy Macon

    Guy Macon Guest

  10. Fred Bloggs

    Fred Bloggs Guest

    The optimum methodology for life extension is to not use it all- anyone
    can see that.
  11. I read in that Guy Macon <[email protected]?>
    Xenon lamps and halogen lamps are not at all the same thing. Xenon is a
    dense inert gas, which allows a higher filament temperature to be
    achieved without excessive evaporation of the filament. Halogens are
    highly reactive elements, and in a tungsten lamp set up a transport
    mechanism whereby filament atoms that escape from the bulk filament are
    returned to it.
  12. Al

    Al Guest

    If you can stand the current drain, put a resistor, value to be
    determined, across the power switch. The idea is to preheat the filement
    without having it glow. This automatically raises the resistance and
    reduces the surge when the resistor is shorted out when you put the
    switch in the ON position. This had been done for eons in military

    The value of the resistor can be determined empirically by putting a pot
    in parallel with the switch. Turn the switch OFF. Turn the pot down so
    the light lights normally, then back off on the pot until the light just
    goes out. Read the value of the resistance on the pot and use the next
    higher standard value that for the switch by-pass resistor.

    If you can't stand the current drain, replace the switch with a slide
    switch that has two positions. In the OFF position, no current flows. In
    the first ON position, enough current flows to warm the filament but not
    to make it glow. In the second position, the battery is connected
    directly to the lamp. The time it takes you to switch from fully OFF to
    the ON position and thru the partially ON position will provide a
    sufficient delay.

  13. John Larkin

    John Larkin Guest

    I've read (an ancient GE appnote, I think) that blinking incandescents
    doesn't really reduce their life. They do tend to die at turnon, but
    they were just about to go anyhow, so that didn't reduce their life

    The resistor would greatly extend life because of the voltage drop.
    Life is inverse on something outrageous like the 12th power of

  14. Guy Macon

    Guy Macon Guest

    (Smacks self in the head) D'oh! I have no idea why I gave an answer
    appropriate for Iodine after reading the word Xenon. Brain fart, pure
    and simple. (hangs head in shame)
  15. I read in that Guy Macon <[email protected]_www.guy
    If it had been krypton, you would have been just one position out in the
    Periodic Table.

    Table, of course, is quadrivalent, so the formula for the Periodic Table
    is Table(IO4)4.
  16. John Doe

    John Doe Guest

    For what it's worth, here are some specs for the Brinkman MAXFIRE
    dual xenon rechargeable flashlight:

    .... current at battery terminal is 2.30 amps with both lamps on
    .... current at battery is 1.16 amps with only the top lamps on
    .... current at bottom xenon bulb when both bulbs are on is 1.13 amps
    .... battery voltage is 6.5 volts
    .... disconnected xenon bulb resistances are .5 and .6 ohms

    The flashlight circuit includes:
    .... two electrolytic capacitors
    .... three transistors
    .... three 1% resistors
    .... eight 5% resistors
    .... two 1N4... diodes
    .... one or two small voltage diodes

    Unless all that is for switching, maybe it already includes something
    for current regulation.

    Here is a blurry picture of the circuit (I need a better camera).

    "flashlight circuit.jpg"

    battery maker is Power One
    part number 04G10 or KT625
    battery rating 6 volts, 2.5 amp hours

    I voided the warrantee, I usually void the warrantee before even
    touching a device. Mind over matter.
  17. As it turns out, probably not all that much difference... Many xenon
    incandescent lamps are also halogen.

    The gas fill in a halogen lamp is an inert gas - argon, krypton, or
    xenon - and the halogen content is only some really small percentage.

    As for life extension by reducing the inrush current:

    Although it is common and obvious that incandescent lamps often, even
    usually die during the inrush, in most cases what happens is that an aging
    filament has a thin spot that has a temperature overshoot during the
    inrush. The filament becomes unable to survive the inrush before it
    becomes unable to survive steady operation. And in most cases not by a
    whole lot - a "thin spot" that melts during the inrush will usually be
    running hotter than the rest of the filament during normal operation, and
    will be evaporating more badly, and that situation will be accelerating at
    a rate increasing worse than exponentially.
    As for the inrush causing actual damage to a filament that is not aged
    to the point of being killed outright by the inrush: What I have heard
    has been mixed, but I believe in most lamps the inrush does not
    significantly damage any that it does not kill outright.

    One bit of data: Those NTC thermistors sold to stick onto the tip of
    the base of a lightbulb have often been claimed to double the life of the
    lightbulb. I once applied one and measured the voltage drop, and found
    that the voltage aplied to the filament was reduced enough to increase the
    life by about 50% even after the thermistor and the lightbulb had fully
    warmed up. Gain of double over 1.5 times, if true, means that reducing
    the inrush would only extend the life by a third in typical household use.

    Keep in mind traffic signals...

    One difference that probably applies to halogen lamps: There is a
    mechanism where their filaments could develop thin spots whose temperature
    is excessive only during the inrush. The ends of the filament, since they
    are cooler than the rest of the filament, may get thinned by the halogen
    cycle. Should there be any halogen lamps where this is an actual common
    cause of failure, I expect they will have life significantly increased by
    reducing inrushes.
    I expect this to be more significant with halogens that are dimmed
    slightly, since slightly dimming a halogen like doing so with a
    non-halogen greatly slows down formation of thin spots caused by

    - Don Klipstein ()
  18. Since most filaments experience most of their temperature rise from a
    cold start in a fraction of 1/10 of a second, I believe most of whatever
    actual benefit there is from inrush protection is achieved if the time
    constant is slowed down only to 1/10 of a second. Maybe as long as 1/5 of
    a second.

    So that 6 H inductor becomes a 1.2 or .6 H one...

    Still does not sound practical to me!

    I think better to use a power MOSFET that has low resistance, a low
    value current sense resistor, and appropriate circuitry to add to this
    to achieve a slow increase in current... and see whether or not there is
    much gain in lamp life - I doubt it.

    - Don Klipstein ()
  19. I read in that Don Klipstein <>
    The inrush current has a cumulative effect. It isn't claimed to kill the
    lamp immediately. Pre-heating is extensively used to combat it, and I
    doubt that would be done if there were no evidence that it works.
  20. John Doe

    John Doe Guest

    Asking the other regular group members.

    Is that an excellent solution with the only drawback as stated power
    source drain? So the small current flow does not wear on the xenon
    lamp? (relatively speaking). If so, that sounds really great.

    In my flashlight application, an additional switch/resistor is
    easily included to short the main switch.


    I hope that doesn't sound offensive in any way to the reply author
    Al. I'm wondering why that workaround hasn't received
    notice/accolades from any other group members. Maybe it's too clear
    for questioning or comment? Thanks again.
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