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xoliilox
04-26-2008, 07:52 AM
Hi. This is my first post, and I can say that I feel I've learned a tremendous amount from these threads over the past few weeks. So, thank you all! A question that has come up for me is about direct driving (with no resistor). I have been experimenting with 18650 batteries (3.7v 2600mah) combined with LUX3s and K2s.

My first question is: I have a green K2 and a green 3 (both ordered from TCSS), and when I directly drive them with an 18650, the 3 is significantly brighter than the K2. This leads me to wonder what amperage these LEDs pull directly from a battery. On the lumileds website it says that a K2 typically pulls 1A and that a 3 pulls also typically pulls 1A but can minimally pull 750mA. On this (TCSS) website, the LED resistor chart says that you want a K2 at 1.5A (which I assume it's not getting?). So, a simple way of asking this question is -- if I put 3.7v into these two LEDs, and there is ample energy to power the LEDs for around/over 2 hours (2600mah), how many amps do each of these LEDs actually pull from the battery? And is there somewhere or someway that I can figure this out on my own?

Second question: I ordered a green rebel mounted on PCB. If I direct drive this with the same 18650 3.7 battery, how many Amps should I expect it will draw? I noticed on the site that I ordered from (led-tech.de) that there is a voltage typical of 3.15v and a voltage max of 3.99v, there is a mA typical of 350 and a mA max of 700, and there is a Lumen typical of 80 and a Lumen max of 145. Does this possibly answer my previous question, that there is a correlation between the amount of voltage that is put into the LED that results in the amount of Amps that it draws? If that is true, it still doesn't explain why my 3 is brighter than my K2...

Third question: I have also tried a Red 3 with the 18650 (I realize that this is a lot of voltage to throw into it) and it works and is nice and bright, is this going to destroy the LED quickly or will it be able to hang on?

I've been running these trials in a pair of Ultra stunt sabers (wraith version), just so you all know.

Thanks for the help!

xwingband
04-26-2008, 10:05 AM
Without a PSU you can't be sure at all what kind of amperage the LEDs are pulling. For example a blue you might have could be 3.4V to reach the 1A while a green might need 3.9V to get there. Without a PSU to test the LED your best bet is to dig into the binning codes and get a "ballpark" figure.

You did touch on it... there is a correlartion between the voltage and the amps to a point. The LED will draw pretty linerally until it hits around the stated max of the LED. After that point it will just suck current. That can be dangerous. Like a Red on a single li-ion is probably pulling loads of current (2A+ maybe even 3A) and I wouldn't keep it that way for long. It will likely go if you used it that way for an extended time and nothing is hurt badly by regulating it.

xoliilox
04-26-2008, 02:14 PM
Thanks for the response. Does this mean that it makes sense to you that the 3 is brighter than the K2? And would you expect the Rebel to be brighter if driven the same way?

Should a K2 be pulling 1500 or 1000 at it's preferred voltage of 3.85 (approx)? And what about a rebel at its preferred voltage? Or are you saying that there is no way of knowing without testing each LED separately? As I understand it a 3.7 li-ion puts out higher voltage initially, so shouldn't this be enough to fully drive any of these LEDs for at least a little while?

This could be why using a driver is the preffered way of dealing with this as one would not need to bother with such musings. Maybe I'll enter that realm soon. Thanks again.

xwingband
04-26-2008, 02:45 PM
Yes, it makes sense. If that III is a lower voltage it's going to get more current than the K2. I would expect a Rebel to be brighter because on the whole they're a lower voltage.

That is why I caution you. You can get away with it but you have no idea what you're sending it and when it goes poof, you'll regret it. You really do need to test each one to know how they'll fare at each voltage. I have a batch of Rebels that are all the same bin and vary from 3.4 to 3.6V.

Also since it seems you're vague on this... a li-ion puts out 4.2V at a full charge. It quickly drops, but at 3.7-3.9V for the nominal that's more than enough to give more than the LED wants. I'll use the Red III since that's a vivid example... you give it 3.7V and it's forward voltage is 2.9 (or even a high 3.4) and it could draw 2A+.

For me personally I like drivers because it's almost "set it and forget it". It won't fry unless I do something else extrordainarily stupid.

Novastar
04-26-2008, 05:39 PM
X could not have said it better!

http://forums.thecustomsabershop.com/showthread.php?t=4648

That thread might help you too, xooiillox or whatever it is, lol! One thing is for certain... be VERY meticulous when doing any kind of "direct driving" (aka no resistor). You really want to know what the heck you're doing.

That being said--I personally do NOT have PSU. But I also don't care how long the LEDs in my direct drive sabers last. I'm pretty certain that they will last for a LONG time... while ALSO quite certain that I *AM* indeed cutting their lifespan in HALF... or more!

Thing is... 100,000 / 2 = 50,000. And let's get wild and say it was even half of that... 25,000 hours usage before it dies.

Well, I don't think these guys are on more than 1 hour each week... but let's double that and say 2 hours each week.

2 hours x 52 weeks in a year (which is ridiculous, because I *DO* go on vacations, and classes will not ALWAYS be happening year round with no break without fail)... = 104 hours.

104 hours per year... divided by 25,000 hours =

...
...

... 240 years of usage.

So... great. I can keep them for like 3 lifetimes... NEVER upgrade the LED... and expect the Li-Ion BATTERY CELL to last 240 years.

Right.

And 240 padawan brains will now fly out of my left tes..... NEVER mind. :)