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White LEDs in parallel

Discussion in 'Lighting' started by Chuck Olson, Dec 1, 2006.

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  1. Chuck Olson

    Chuck Olson Guest

    Never do it, they say. Some LEDs will hog the current, they contend,
    resulting in brightness differences that make parallel operation totally
    impractical. But now this is the latest way to build flashlights with many
    LEDs in a "shower head" configuration. Manufacturers in China are producing
    LEDs that either have identical forward voltage within very tight limits or
    maybe they are sorting useable sets from raw factory output. In any event,
    the sets successfully operate in parallel with very little difference in
    brightness. My 128-LED flashlight is setup in 5 sections with 5.6-ohm
    resistors in series with each group of 38, 31, 24, 18 and 17 paralleled
    LEDs, all strings supplied from 9 volts of AA cells. My 32-LED flashlight
    has all 32 in parallel, connected to 4.5 volts of AAA cells with no series
    resistance. If you put good, low internal resistance NiMH cells in either
    flashlight, it really goes bright! The currents per LED with alkaline cells
    run in the vicinity of 20 mA, with each LED rated at 11,000 to 15,000 mcd,
    so the clusters put out gobs of light, easily surpassing the optical levels
    of 3 and 5-watt single LED sources.

    The finished products seem to be very practical, and are amazingly
    inexpensive. Each 32-LED flashlight I bought cost $4.99 plus tax and
    shipping or $10.40, and the 128-LED flashlight cost $30. With each
    flashlight constructed in anodized aluminum with quality you would expect in
    a U.S.-made Mag-lite, how can you beat that?
     
  2. My 100 LED torch has every single LED in parallel with a single resistor
    from the 6V AA pack.

    The Chinese manufacturers can specify LEDs with forward matched
    voltages. I've had some nice Xmas lights that have absolutely perfectly
    matched LEDs that even maintain equal brightness down to the last ounce
    of power in the battery.
     
  3. Oh bugger! Am I that predictable.

    It's more of an "Oh my God, look at this!" type of LED pissing match
    product anyway. I'm not sure something that draws 2A from AA batteries
    is really practical. :)
     
  4. Somehow I think that an LED flashlight can now draw .5 amp (or even
    no more than the below incandescent does) from a series pair of AA
    alkaline cells and recently nowadays significantly outperform
    the traditional incandescent flashlight lamp targeted towards a series
    pair of AA cells. The incandescent that I believe this refers to isthe
    PR4.

    - Don Klipstein ()
     
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