WF-500 with Soul P7 and direct drive - which resistor?

waTom

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Hi,

I would like to mod my cree-module for my ultrafire wf-500 with a p7. Since I haven't found a cheap driver for it I thought of using a resistor and direct drive.
I'd like to use two 18650s but, unfortunately, my knowledge of electronics is rather small.

Is there a formula to calculate the right resistor value (do I say so?)? And do I need a special one because of the highter wattage?

Regards,

Tom
 

mash.m

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you don´t need a resistor. you always write it down - direct drive!

markus
 

jirik_cz

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you don´t need a resistor. you always write it down - direct drive!

markus

Are you sure? waTom wants to use 2x18650 :D:poof:

But resistor is not a good idea, it would be very ineffective. Unfortunately AFAIK there is no suitable driver for P7 and two liions yet :( You can only use two SOB drivers (from sandwich shoppe) in parallel.
 

Stillphoto

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Glad I stumbled upon this thread...I've been thinking of a similar mod. 17670's wouldn't change anything in the equation I assume. My 18650's wont fit.

I was just thinking of some sort of DD slug to hold a P7.
 

waTom

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But resistor is not a good idea, it would be very ineffective. Unfortunately AFAIK there is no suitable driver for P7 and two liions yet :( You can only use two SOB drivers (from sandwich shoppe) in parallel.

Unfortunately, the two SOB drivers from the shoppe are too expensive for me.
How much energy would be wasted due to the resistor?
 

jirik_cz

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In this configuration it will waste around 50% of power. So you will not get any runtime advantage from using 2x18650 and as mash.m suggested, better use one 18650 in direct drive :)
 

mash.m

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sorry i didn´t read that you want to use 2 18650 in series! with this configuration you need a resisor with ca. 1,5 ohm and 10watt´s. there will be a lot of heat (7.5watt) !!!
this is not a good idea. my tip, use only one 18650!

markus
 

jasonck08

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A 18650 dummy would do the trick as mentioned above.

If your light has enough room in it, you could modify it to run in parallel with some wire and a couple metal washers and some rubber ones. I just made a simple diagram showing you what I'm talking about...

View it here:

light%20diagram.png
 

jasonck08

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Yes, PCB is not a bad option if you can find it. A thin sheet of copper would work well too. Also, just noticed that for some reason it says "rubberrl" instead of just "rubber" strange, but no big deal.
 

smopoim86

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I made a 2 18650 holder like that for my 3c mag. It took a lil effort and i'm pretty sure there is no way to pull it off in a light designed for 2x18650. (not enough room for wire or spacers)
 
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