Best LUX III BIN For Fatman?

Im going to run a 3 LUX III's of a Fatman powered by 8 NIMH AA cells. They have 1.4v when fully charged and 1.2 nominal, so what would be the best Bin for this setup. They'll have 11.2 volts at max charge and 9.6 at nominal. I know theres some experienced Fatmen out there that have the answers I need. I was thinking a J BIN, but I'm not sure how the chip works. If I overpower the LEDs a bit will the current just bypass the chip until it drops to the right setting I have dialed in? If so I don't mindboosting the LED's until it falls into regulation. I have some that handle 1200ma easy properly sinked? So throw any info you have at me and I'll digest it.

Under any reasonable load the 8 nimhs will go to 1.3V pretty quickly. That's 8 x 1.3 = 10.4V. So, 10.4/3 ~ 3.4V Vf each would be just fine at 700mA+ on Fatman. If you Vf is lower and your batteries are higher Fatman will essentially go direct drive - basically DC will flow through the inductor/schottky. J bin Lux3's should be very safe in this configuration.

More the issue is dimming, if you plan to dim Fatman then you may lose some dimming range with lower Vf Luxeons until the batteries discharge somewhat.

What output current do you plan to run Fatman at?

george.

Was planning at running them at 1 amp, I read that I need to go a little higher on the Fatman to achieve 1 amp though. And I did plan on it dimming it. So apparantly the dim function only works in regulation mode.. makes sense. So what would be a good BIN for 1 amp, I was under the impresiion that if highest voltage is applied the LUX's run at 1 amp and if higher than spec then overdrive.

heck even 1.2 amps each would be fine I think the fatman can do 2 something total.

elfen1 said:

heck even 1.2 amps each would be fine I think the fatman can do 2 something total.

Click to expand...

No, Fatman can handle about 2A (bit more, but 2A is conservative) on the INPUT.

You can find some of the equations/facts on what works and doesn't on the Fatman tech section of the TaskLED website. You need to consider input/output voltage and input/output current to determine whether it is in the safe operating range and how much power is being dissipated in Fatman. It is a fairly efficient driver, but even at 90% 10W output still requires nearly 1W to be dissipated by Fatman. So, on the higher powered designs you do need to provide some thermal path from the back (non-component) side of Fatman to the case.

Yep, dimming occurs as part of the current regulation. As you dim the output current lowers, of course than means the Vf of the LEDs also lowers. If that lowers to the battery voltage, then you can't dim any lower since the battery will just direct drive through the inductor/schottky path.

george.

I had some trouble calculating what BIN I need using the equation. Basically I want to run 8 NIMH with the fatman at 1 amp for the LUX III's in series. I'm trying to maximize efficiency yet don't have the board so its all specualtion right now. Anyone out there have a better explination on the calculation for the Fatman or better yet what BIN would be best from experience. The calc says use the lowest voltage the Batts will produce but I'm sure thats like 1 volt near disharge levels. So I'm up in the air.... P.S anyone know if Titanium NIMH cells will work with the Sandwich Shoppe 2D-8AA convertet?