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White LEDs in parallel

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Chuck Olson

Jan 1, 1970
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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?
 
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Clive Mitchell

Jan 1, 1970
0
Chuck Olson said:
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 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.
 
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Clive Mitchell

Jan 1, 1970
0
Adam said:
Clive will be along in a minute to rave about his 100 LED `showerhead`

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. :)
 
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Don Klipstein

Jan 1, 1970
0
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. :)

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 ([email protected])
 
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