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Maximum voltage that a bulb can take before burning out?

  1. Nov 24, 2006 #1
    is it possible to measure the maximum voltage that a bulb can take before burning out?

    I am interested in using rechargeable batteries for a 9v tactical flashlight that I have, but rechargeable 3v batteries actually have a peak voltage of around 3.85 when fully charged. As the bulb is kind of pricey, I don't want to burn it out by putting in rechargeable batteries.

    if it's not possible to measure the maximum voltage for the bulb, is it possible to put something in the flashlight circuit to limit the peak voltage to 9 volts?

    thanks in advance
  2. jcsd
  3. Nov 24, 2006 #2
    1. The no load charge voltage on a battery is different to the load voltage. When you actually load the battery it will drop rapidly down to the nominal cell voltage. It is this nominal cell voltage that you need to use.

    2. There is not really a maximum voltage for a lamp as opposed to a survival period. The more volts applied the brighter you burn the shorter you live. Something I tell new staff when working on high voltage systems.

    As a rule of thumb you can derate bulbs using the following equations:

    Life = Rated Life * (Rated Voltage/Applied Voltage)^12

    Intensity = Rated Intensity * (Applied Voltage/Rated Voltage)^3.5

    Current Draw = Rated Current * (Applied Voltage/Rated Voltage)^0.55

    Note that as you get further away from the rated values these equations get less and less accurate so don't try and put 240V into your 1.5V bulb.
  4. Nov 24, 2006 #3


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    Gold Member

    That would solve Aki's rocket ignitor problem... :rolleyes:
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