how to power 4 X-REs from li-ion batteries

I am building a light using 4 CREE X-REs and want to power them at 1.4 amps each from a Li-Ion battery pack. The pack voltage should be high as possible for the largest power density, I want about 4 hours burn time.

I bought the DX 1.4 amp AMC7135 1400mA Regulated Circuit Board and planed to put it in series with all the LEDs and 4 Li-Ion cells but then I realized the max input voltage is only 4.5V and Vf of the led is around 3.5, so in this configuration the driver would be faced with a much higher voltage than it is rated for.

I am not worried as much about cost as I am building a robust light, can someone please suggest the best driver and configuration to drive 4 XREs from LiION cells?

Thanks,
Brandon

You could get 3 more of these and run a driver to each XR-E. Run your 4 Li-Ions in parallel and feed all 4 drivers also in parallel.

...Actually you may be able to get away with fewer drivers, there is a trick involving using an LED on the input side as well to take advantage of currents being balanced I think.

Ok found the picture, rehosting it:


I think if you add one more Li-Ion to this example and add one more XR-E before the regulator it could work. This works by reducing the voltage seen by the regulator as each XR-E will roughly balance off the inline voltage of a Li-Ion. So the regulator sees more like 4V, rather than around 12V for 3-Li Ions. And those 3 XR-Es before the regulator are still pulling the proper currents. Oh and you have the 4 x 7135 driver instead, but it should still work.

I'd wait to see if someone else can confirm this first.

I would recommend LuxDrive's PowerPuck (1A version) from LED supply.

http://ledsupply.com/powerpuck.php

You'll find the data sheet on the web site.

Thanks for the reply Wiggle, what you are describing is exactly what I was trying to describe. I believe that if the Vf of the LEDs is 3.5V, and the Li-Ions are fully charged, at 4.2V? then the driver would actually be seeing 4X4.2-3X3.5=6.3V, too much since it can only handle 4.5V.

Or am I wrong?

GTRio said:

Thanks for the reply Wiggle, what you are describing is exactly what I was trying to describe. I believe that if the Vf of the LEDs is 3.5V, and the Li-Ions are fully charged, at 4.2V? then the driver would actually be seeing 4X4.2-3X3.5=6.3V, too much since it can only handle 4.5V.

Or am I wrong?

Click to expand...

I had 6V somewhere in my head for 7135 for some reason. I don't think 6.3V would be exactly a disaster.

Edit:Just confirmed 6V for AMC 7135. Also, Vf will be higher at 1400mA, it's already 3.7 at 1000mA on avg, probably close to 4V at 1400mA.

The AMC7135 recommended limit is 6V. The absolute max spec is 7V.

If the input is 6v then cool, I got 4.5V from the DX description.

Vf on these R2 X-REs is only 3.5V at 1.4A, I measured it myself.

I will try building it with these drivers and see what happens,

thx.