Cree XT-E White announced

[AnAppleSnail]

I never thought to home make a 2aa direct drive for the kids and bed. Did you measure current? Who has these cheapest on star? The typical 3aaa 9 led light draws(along with some fixed, built in resistor ) about 11ma from nimh 2aaa. Fine for kid reading light, which is left on all week. Xte should be brighter.

I hadn't bothered to measure current. I tend to pick a resistor value giving .3 to 3 lumens. That suggests a current around 1 mA. On a well-settled C NiMH, I get about 20 lumens with no resistor. That would suggest about 30 mA, but I never measured it. I think Cutter had them at $4 on a star. No line breaks! I have a bare XT-E at 1-30 mA, and of course no heat problems.

 

[AnAppleSnail]

Using the Cree data from the Product Characterization Tool, and data from the Eneloop datasheet, I put this together. With 2 Eneloops, the starting voltage per cell is 1.45v, giving 2.90v to begin. This suggests a current of 210mA, giving 90 lumens from an XT-E R4 bin. I will have to insert my table as an image. These are calculated values, not measurements. Using interpolation, I can calculate the change in the Eneloop voltage based on current draw, and then the change in LED current and output based on the new voltage. That allows me to predict an initial output of 90 lumens, dropping to 64 lumens after 10 minutes. Incidentally, the ANSI FL-1 output of a bare XT-E on 2 Eneloops would be 90 lumens for 1.8 hours. After 1.8 hours, the LED would be running at 9 lumens (6 mA), and have only consumed 100 mAh of capacity (95% remaining).

Extrapolating the Cree data beyond this is not reasonable, and we would need real measurements.

 

[degarb]

Of course you are using a variable resistor, so infinite control and longer runtime.

What potentiometer are you using? Jameco has some that might work, cheaply (would any of these work?). I was a big fan of the instant gratification, Radio Shack $3 25 ohm (if I recall correctly) variable (modifying direct drive and china controller that are not fixed current), until I got addicted to the Buckpuck with its dimmer (ledsupply and other sources).

Undoubtedly, logically, the way to go for sub $10 low-lumen lights is: 2 AA + cheap electronics + removable tir (dirt cheap and swappable beam patterns) + highly efficient & accesible led, but not over priced. Though my xte was white with no optic, but wanko colors with reflector, never tested with tir.

My daughters hang onto lights fairly well, maybe a loss every 6 months. Wife and son can loose one or two light a week. Price matters.

 

[AnAppleSnail]

I built this with a 100 ohm resistor. I measured 4 mA and 2.7v at the LED. That's about right for 5 lumens, similar to a Mag Solitaire. This should get about 200x the runtime though.

I like audio tapers for the nicer dimming. This doesn't use a potentiometer, but my lightbox does - A "stereo volume" potentiometer. If I wire to the right pins, I can push-in the knob to turn it off.