When the battery is fully charged, it will be 4.1-4.2 volts. When discharged, maybe 2.7, maybe 3.0V, maybe higher or lower. Depends on what you (or your battery's protection circuit) call "discharged". The XML wants about 3.35V all the time. Can you see the problem here?
The driver is supposed to correct the difference between what the battery supplies and what the LED requires.
For your parts, I would suggest you run 3S2P battery configuration (that means strings of three cells in series, two strings in parallel). Then get a driver that can handle 8-13V input range, and has either 3A or 6A output. For a 3A output, run the LEDs in series. For a 6A output, run them in parallel. You could also get a 2.8A driver and run the LEDs in series. If you have a 6A output, a 2S3P battery configuration might be more efficient. The difference in runtime would probably be small, but the input voltage range would be only up to 8.4V.
For high quality drivers I would go to Taskled (he's a CPF member and valuable contributor), or there are a few others whose names escape me. One is in Germany. For cheap drivers go to DealExtreme or Kaidomain. There are others, but Taskled, DX, and KD are the three most commonly discussed on CPF.
Another possibility for using all cells in parallel and all LEDs in parallel, you can get AM7125 drivers (from DX or KD), or an IS1006 (from me). The drawback (or possibly and advantage) with this setup is that the light output starts to drop before the battery is fully discharged. Also, if you have a battery protection circuit (highly recommended if there is any chance of over-discharging the cells), the light will cut off with no warning when the protection circuit kicks in. Some of the other drivers will give you warning when the battery is low. If it's important to you, check the driver details before buying.
Lastly, if you really don't want to use a driver, you can use a simple resistor. This should limit the maximum current to a level that's safe for the LED. The drawback is that the light output will beging to drop immediately when you turn on the light, and will drop steadily as long as the light is on. The setup you tested is like this, except the resitor is the wires, LED, battery resistance, switch resistance, etc. all added up. It's probably not enough to resistance to protect the LEDs from overcurrent, which may dramatically reduce their lifetime. With or without a resistor, this is called a Direct Drive setup. With DD setups, many things matter that don't matter much if you use a driver. Battery connections, wire size, wire length, switches, LED specs, all matter and can change from one light to the mext.
To be honest if you are running those XML LEDs on a star, direct drive on li-ions I am surprised they are not dead already. Have you checked the current running to them. I'll bet on a fully charged pack your driving them over 5-6+ amps per LED. Plus that is really not much metal for a pair of high powered LEDs anyway. Even with the current regulated to 3A per die its still gonna get warm.
I recommend using the "SSC P7 8x7135 2.8A 1-Mode Circuit Board" from Kaidomain. One for each LED. They are cheap and easy to use.
Last edited by vestureofblood; 07-14-2012 at 09:55 PM.
In Him (Jesus Christ) was life; and the life was the light of men. And the light shineth in darkness; and the darkness comprehended it not. Shorty C/D M*glites
I don't know the best way to read current, but with chinese multimeter reading + and - give me 7a, and 4,05v. (for current I put black and red wires from multimeter on the + and - poles of batteries...)
My batteries are sku 19770 from DX.
To correct voltage can I use a Diode to drop voltage? Or between it and resistor, the resistor is the best way?Or the best way is buy a driver from DX and wait +30 days to receive it?
I Live in Brazil (with my poor english) and is hard to find high current drivers!
if you told me that this drive work in "on off" mode i will buy it (DX sku 57779)
I will not use this "setup" as a flashlight, it's just a hobby, so I don't need low battery warning (i think)
I drive this led with star and PC heatsink, with only 2 batteries leds and heatsink gets warm, but with 4 more batteries gets hot a lot
Can you recommend any DX driver?
Wow! You're lucky you haven't burned something yet.
That's NOT the way to measure current. The way to measure current is to have a complete circuit (like battery and LED), then open a connection somwehere and put the meter to the two sides of the open connection. Unfortunately, the meter will reduce the current, because it has a resistor in it when used to measure current. What you did was to measure the short circuit current of the battery. That should have been 30A or more if you measured all six cells.
The DX 57779 driver should work well with the battery re-wired for 3S2P and the two LEDs in series.
If you are in a hurry I have an IS1006 in stock I could modify for 6A and ship on Monday. With this one you'd keep the battery in 1S6P configuration and run the LEDs in parallel. USPS Priority Mail to Brazil is probably 6-10 business days. With shipping it would cost $42.95 USD though, so it's not for the guy on a buget!
I doubt that heatsink is enough for two XMLs at full power. You'd be putting around 20W into the heatsink, and it would need a good fan to keep cool enough at that power. Also, the batteries should be kept away from the heat as much as possible.
Thanks all for help.
I married a month ago and now I don't have extra money to spare with drivers and leds (price, import tax and other things necessary to do a flashlight), Until december I won't buy driver, but after, I will do my flashlight.
Now, I have a little knowledge to do it, now it will be easier, i guess.
After, I'll return to forum to take off my doubts.