IR Led Flashlight

[redsox985]

I am modifying a piece of junk 9 led flashlight (the kind at auto store checkouts). I am attempting to convert it to IR by heating the solder on the current PC board and removing the white leds and dropping in IR ones from RadioShack or where ever you suggest (please do if you know of somewhere better they dont need to be high quality just work). I know how to solder but I am unsure if I need resistors for each led or if i can get ones that have the right tolerances. The victim uses 3 1.5v aaa batteries so by my basic math that equals 4.5v in and 9 leds out meaning 4.5/9= .5v per led??????
help please

 

[Al Combs]

I looked in the Shack's list of LED's and they only have one that's IR. The specs say its forward voltage is 1.2 volts and 100 ma current. That's roughly 1/3rd of what a typical white LED would be. So there's a good place to start. If you wire them 3S3P (3 serial & 3 parallel), they would have roughly the same equivalent voltage as their white counterparts. You are correct about wiring LED's in series being the better way of doing it. In parallel the one with the lowest forward voltage, will draw the most current and blow first. There's just not enough voltage to work with in this case.

Those cheap 3*AAA battery multi LED flashlights work on the premise that the load represented by a bunch of LED's in parallel and the high internal resistance of a battery that small will balance out. Actually the crappy batteries most of the throw-aways include have a higher voltage sag than alkaline batteries and are part of the design. That's OK for a $2 throw-away flashlight, but too risky @ $18 for 9 IR LED's. Your three parallel strings of 3.6 volt 3 series LED's will draw ≈ 300 ma total. The SilverFox alkaline battery shootout only goes down to a 500ma load. But at that load level, all the AAA alkaline batteries he tested start out slightly over 1.4 volts. I entered into the LED Calculator Program 80 ma (conservative), 3.6 volt LED, 4.2 volt battery and 3 parallel LED. It says you need a 2.5 ohm 0.14 watt resistor. Maybe a (4S2P) arrangement leaving 1 LED out would work better with no resistor. Do you have a multi-meter to test it?

Have you considered buying a cheap IR light? Part of the reason I modded a lot of lights was for the sheer fun of doing it, so there is that. Actually all of my mods made perfect sense until my wife asked me what I was doing.

Happy modding and :welcome:

 

[alpg88]

first, radio shack leds suck, big time.

i've build ir array using e bay 200mw 10mm leds, they are rated 100ma at 1.5v 100ma. my array has 12 leds, no matter what ppl say about e bay stuff, they are the best ir leds available (i mean in 5mm- 10mm type).

putting many leds in 1 array, you are bound to some in parallel, for practicality reasons.
i had 2s6p, i used cr123 cell, the whole turned out very compact, all fit in small radio shack enclosure, i also installed hot shoe clip, i used this array on my sony cybershot camera, it had night shot feature, this was the reason i build the array, ir stop filter was opened once night shot mode was on, the array was a great flood light, good for 20-25 meters the most. not a thrower. i liked the way it turned out and would build another one if i had to in a heartbeat, (this time i'd use cree ir drop in as well).
but i sold my sony camera, with all accessories, including this array, i,m planing to buy dslr soon (if i don't waste money on something else before).

however, as good as that array was imo. there are ir cree led drop ins (with reflector, led , driver all in one unit).
as for wiring and resistors, this might help
http://wolfstone.halloweenhost.com/Lighting/litlpo_PoweringLEDs.html

 

[redsox985]

Thanks for the pointers and links. I'll most likely pick up that cheap one from DX just for the sake of simplicity why build my own set up in a disposable flashlight for about 4 times the price of the ir one on DX. Thanks for you help.:thumbsup:

 

[SmurfTacular]

Beat me to it. DX has OK IR LED's, and there really inexpensive. But there shipping time is awful. about 15 days for the average delivery.