Mag3D Single LuxI LED Current question

Hopefully this is the proper place to post this, if not please move....

Ok, I've built a couple K2 3C mag conversions so far, but I had ordered a Royal Blue and Blue LuxI emmiter from sandwich shoppe to do some 3D mags.

Tonight I put them together, previously I had the royal blue temporarily in a 3C mag without any problems (seem to recall amp draw seemed ok)

Now I have them permanently installed, of course I didn't get Vf for the LED's when I bought them (Bin codes weren't listed/available)

So I built them, they work great, plenty bright, etc...

I put my multi-meter on the 10A setting, and placed the negative on the back of the batteries, and the positive on the lights body, and with 3 cells I get almost 2AMP (1.8-2.0 ish) so this made me go, hmm, overdriven big time... so I pulled one cell out of one of the lights and checked the draw again, this time getting .22 or so on the meter... This to me seems like what I should be seeing, but I find it hard to belive that there is such a difference between one cell to the other...

I don't know a lot about electronics, and am trying to learn what I can... is there one of the formulas (such as ohms law, etc) that explains what I'm seeing? I'm not great with math either, but is this the difference in 1.5V does it really add about 1.8A more current to the circuit. .22Amps seems under driven as if memory serves LuxI's are speced at 350ma, I know I could overdrive a little, but 2A has got to be enough to fry them in a short time frame I would think.

So, help me understand what's going on, if I'm doing something wrong, or 1 cell really makes that much of a difference.

I guess the solution is I need to get a dummy D cell and run them at the .22A rate, or get a converter board, which board should I get, simple easy to install and configure... I want to lean to use converter boards (regulation, etc) eventually I'm really interested in the multi-level converters, but it looks like they require that voltage be supplied from the batts to the board, and then a seperate switch circuit, so I'm guessing I would have to do something different besides just placing it inline from the switch to the LED


Help me understand, and please reccomend a solution, I'll order a dummy cell for each light or converter from Sandwich shoppe (or ???) on monday to fix these lights up proper.

[Edit] I know I can add a resistor as well to fix the voltage/current difference as well, which might be the solution to the blue light since it won't be used as much, but I want to learn how to use the converter boards, and if I'm going to tear it apart to fix it, I might as well learn more and add regulation to the mix, especially on the Royal Blue which is likely to see more use. [/EDIT]

Try this very handy program.
http://www.jtice.com/led_pro/led_pro.htm
Norm

Thanks, I downloaded that just a little while ago, but couldn't get it to work, since the only values I know are the battery input voltage, and what the LED is drawing in current when on. I don't know the Bin Code on the LED to know the Vf or any other information...

If you have a variable power supply you can find the VF of you LED by starting around 3 Volts and increasing the voltage until the current reads 350mA. then read the volts and you have you LED's VF.
Norm

Unfortunately I don't have any equipment like that, all I've got is a soldering iron and a couple multi-meters.

Maybe I can find a power supply at the electronics supply for not much money and test that way... I'm wondering if I shouldn't just order a Downboy 400ma Converter from the sandwich shoppe for the one, then I can figure out what to do with the other light later, whether it be resistor, or just drop in a dummy D cell.

You could start with a 1 ohm resistor is series with your three batteries measure the current, if it's too high increase the value of the resistor, if it's too low decrease the value.
Norm

Willabbott said:

So, help me understand what's going on, if I'm doing something wrong, or 1 cell really makes that much of a difference.

Click to expand...

Straight from the Luxeon Data Sheet
( http://www.luxeon.com/pdfs/DS25.pdf ):





You can see that one cell really does make that much difference. That's why LED's, or any diode, is considered a "current device" vs. a "voltage device". It's much easier to control it's operating charactistics via the current, instead of the voltage.

With adequate heatsinking (a DHS or Hotlips D size ), I've run 1.4 amps through a Lux I SX0H device 20 minutes at a time. (Single 18650 Li-Ion cell) Much above that, I'd probably use a resistor.

Thanks for the info guys.. I guess LED's are more sensitive to voltage than I thought... (Still learning what I'm doing here)

I'll look to see what I can get a variable power supply for, as I'm sure I'll likely be glad I have one later down the road. I'll also see if I can't pick up some packages of resistors to have on hand, again knowing I'll likely need/want them later.


And probably order a 400ma or 500ma Down Boy converter for the one light, it would be a good experiment light, and nice to know how to use the board, and would likely be good to have regulation on the royal blue as opposed to a resistor.