Help me out with resistors

TB383

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Hello, I am doing my first mod ever and am following the great write up that 3rd shift did for a 4d Mag converting to a k2 led. Anyways the local store here does not have a 5 watt 1 ohm resistor that 3rd shift says to use in his write up, so I was just wondering if there is another resistor that can be used in its place. Thanks for the help

Travis
 

yellow

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First: ask at Your shop if they have the 4 watt version,
if not get 2 (two) pieces 2 (two) ohms / 1 watt resistors and use these in parallel
(thats them being used side by side, not in series)

the "larger" 4 and 5 watt versions are better when used alone on a circuit board, but here You glue them to the heatsink. That way getting the heat away is no problem. Also there are less than 2 Watts that the resistor has to stand, should work without problems.
 

mudman cj

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Edit: Whoops, I did switch the resistance and power numbers before. 3rd shift used a 5W, 1 Ohm resistor in the 4D K2 write up. It draws 1.2 amps on fresh batteries, so at most 1.2*1.2*1=1.44 Watts is being dissipated through the resistor. Yellow is right about being able to use a 2 Watt resistor with a 1 Ohm resistance. You could also use two 2 Ohm resistors in parallel like he suggested with ratings of at least 1 Watt each, or you could use two 1/2 Ohm resistors in series with ratings of at least 1 Watt each. Sorry if I created confusion, and good luck!
 
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yellow

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but there is a value of 1 Ohms needed (at 2 watt).


btw: I am not totally sure about the initial current, and would suggest a higher ohms value.
But this is direct drive and I have not much experience with it (as I hate this extremely low tech mod)

how about using a suitable driver board?
Not this much more different and fits perfectly at the space where the resistor would be placed.
Holds the output of the led at the same level, while Your "direct drive" dimishes in output VERY, VERY much within the first 5 mins, then very much for the next 10 mins, then much for the suiting 1/2 hour and after about 1-1.5 hours the reduction in output gets smaller and smaller but stays, of course.

Maybe plan for a change in the future and leave the wires to the led a bit longer and do not use excessive glue to be able to remove the resistor(s).
 

Ra

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Driver-boards do have their atvantages, but simple resistors do as well !!

Some like the continous level of output with a driver-boards, some like the simple and more reliable setup with resistors:

I have seen driver boards that failed.. I have never seen a resistor that failed.

You do have a powerloss with risistors but: Driver-boards have an efficiency of about 85% tops, thats also is powerloss. With the right setup, powerloss with risistors is less compared to the powerloss with driver-boards.

I have experimented with both, and found the reliabillity of resistors as most inportant. So I'm using resisitors in all of my LED- and Luxeon-flashlights.

And I never experienced a severe lumens-drop in the first 5 minutes (at 1.5 amp high power) !!

Ofcource, there was a powerdrop, but to the eye hardly noticable, because it gradually drops to a level where the batt is almost drained, then it suddenly drops faster, indicating it needs a charge..

High quality cells keep their nominal voltage for most of the charge, after that, the voltage drops severely.

Regards,

Ra.
 

TB383

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I think i am going to just stay with a resistor because of the reliability issue. This is going to be a light that will get abuse and need it to keep on working.... Anyways, I am found out about another store that carries some but they are not open on the weekends, so got to wait untill monday. If they dont have it, i guess ill have to buy one online somewhere.
 
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