Resistor value for a direct drive D26 drop-in

I blow up :mecry:a D26 drop-in driver (the LED a P4 Cree is OK). I works on 3.7V, it works on 2*3.9V but once the battery recharged . Now I want to drive it directly (throu a resistor) from one 4.2V down to 3.8V batterie (18650 2200mAh theoreticly actualy ??? my be 1.8Ah). I need one houre run time (for the longest travel with my bike) as bright as possible with no danger for the LED. After looking in the Cree P4 data I choose 1 ohme 1W.
Is it OK. Any other suggestions ?

By the way the D26 module is not easy to open. After unscrew it do I have to unsolder the leads to LED to be able to open it or do I have to pul harder ?

Here is a good program to calculate resistor values. It says you need a 0.5 ohm half watt resistor. That's for a 4.2 volt battery, 1000ma and 3.7 volt @ the LED. Of course it's just an estimate since LED's don't obey OHM's law. There are always slight variations in forward voltage from one LED to the next. You can't really say an XR-E will draw 1000ma @ 3.7 volts, but if it did...

Usually the driver is either solder or epoxied into the pill. Got any pictures? What about replacing the driver instead of using a resistor? One of the AMC-7135 variants should work very well with an 18650. Try searching DX's site for "7135".

Thanks. The calcolator don't work on my computer. Tomorow I'll try on another.

I have seen some LED calculators that use Java script. This one however is an actual program. The thing on the right side of the page is only a picture of what it looks like. Did you click on the Download Here link? It doesn't need to be installed, just download to your desktop.

Ok I found the pb is my french keyboard. To make it worke I need to enter decimal data e.g. notpad then copy and past and then it works.
Thanks a lot

I would use an AMC7135 board instead of a resistor.

yea, screw a resistor, try to order up a regulator board instead, like the one that LukeA is suggesting.

Heck, for $10-15 you can replace the whole drop-in with something reasonable from DX. And get a higher bin emitter to boot.

Eric