Resistors necessary in18 LED DB conversion?

Gandalf

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Jul 3, 2001
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I have one of those 18 white LED conversions built on a 6AA Energizer Double Barrel. My question is about the resistors on the PCB. There are 6 resistors, 3 LED's per resistor. The color code, if I'm reading it right, is gold, black, red, brown. My question is whether these resistors are even necessary. I have a Trek 7 light which uses no resistors or current control circuit at all. There are 7 white LED running off 3 C cells. They appear brighter than the white LED's in the DB conversion. It seems to me if 7 LED's can run off 3 C cells without resistors, do 18 LED's running off 6 AA cells, 2 sets of 3 AA cells in parallel, need resistors to drop the voltage? It's like having 9 white LED's running off of 3 AA cells. Advice from those with more knowledgeable than I about LED's and operating voltage will be greatly appreciated.
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papasan

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Mar 25, 2001
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well...i've run a single LED off of 4 D cells before for about a day straight just to see if it would work...it was real bright, let me tell you!...it was open air, so heat build up wasn't an issue...

off of 3AAs i think you would be fine...remember that not all LEDs are created equal...even the same model from the same manufacturer can be night and day different, so perhaps some LEDs would die from this over-driving...

also, i put a single LED onto a 9V battery just to see what would happen...blew up into a million little pieces...only piece i found afterwards was one of the leads...happened very quicky, like 3 seconds...

a friend put 3 or 4 LEDs (i forget exactly how many) into a petzl duo headlamp (4AAs) and used high capacity NiMHs with no resistance...the heat generated caused the reflector to discolor and warp but the LEDs where still useable afterwards...

it seems that white LEDs when they are overdriven too much get a very blueish tint...something to watch for while you experiment...

all-in-all your probably safe, but just use one barrel first to see what happens and be ready to shut it down fast if the color starts to go blue...
 

ElektroLumens

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Gandalf:
I have one of those 18 white LED conversions built on a 6AA Energizer Double Barrel. My question is about the resistors on the PCB. There are 6 resistors, 3 LED's per resistor. The color code, if I'm reading it right, is gold, black, red, brown. My question is whether these resistors are even necessary. I have a Trek 7 light which uses no resistors or current control circuit at all. There are 7 white LED running off 3 C cells. They appear brighter than the white LED's in the DB conversion. It seems to me if 7 LED's can run off 3 C cells without resistors, do 18 LED's running off 6 AA cells, 2 sets of 3 AA cells in parallel, need resistors to drop the voltage? It's like having 9 white LED's running off of 3 AA cells. Advice from those with more knowledgeable than I about LED's and operating voltage will be greatly appreciated.
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<HR></BLOCKQUOTE>

I have a conversion where I put 20 LED's in a 4 'D' cell MAG LITE. I had no problems whatsoever. One of my favorite LED mods is to put 12 white Nichia's in a 3 'D' cell flashlight. I use the Rayovac 3 'D' cell Industrial flashlight. This works great, and I have no problems at all with them being overdriven.

You should take the resistors out of that DB mod, and then it will shine much brighter. I have this same flashlight, and as soon as I get around to it, I plan to mount 20-30 (whatever will fit) white LED's in it. I will use no resistors at all. There is no need. It has something to do with the amount of current being drawn in relation to the voltage. That's about all I can tell you. The more current (more LED's), the less the need of resisting down the voltage/current.

Of course you must realize that the life expectancy of the LED's will be shortened. Maybe instead of 10 years continuous use, you might get 5? Big deal!

Within the next few weeks I am putting 20 white Nichia's in the 3 'D' cell flashlight for a friend. This is a very nice, very bright, very long lasting flashlight.

I am also experimenting with the Luxeon Star, and with step-up and step down regulators. With the Luxeon, we need to be exact in the voltage/current being supplied.
 
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