1.2A Buck Regulator?

I've been snooping on CPF for a couple of months now and this is my first post!

I want to mod one of my old D Mags. It will be an aspheric with a Cree XR-E R2 bin that I'd like to crank to 1.2 Amps. I'm thinking about using the 2D to 8AA adapter from the Sandwich Shoppe. That would mean I'd be running 12 volts into a buck converter and stepping it down to 3.9ish volts (at 1200mA). Now for the questions...

Question 1: Assuming a poor regulator efficiency of 85%, my current from the batteries wouldn't be more than .5 Amps, right?


Question 2: Will the AA's have a problem driving this load?

Question 3: I can't seem to find a buck regulator that can run the 1.2A to the single Cree (all I've found is a bunch of 1A units). Does anyone have any suggestions for this regulator?

Question 4: I've been looking for a long time for a D Mag heat sink that I can put the single Cree on (all I've found is triple/quad or more LED heat sinks with a big hole right where I want to place my single). Can someone point me in the right direction?

Whew! I apologize for the long post. Thanks in advance for your help!

-zambai

1. At the voltage you are looking at, 85% would be average efficiency, I would use a lower number. With your numbers, yes, it would bea bit less then 500 mA from the battery.

2. At 500 mA draw, most AAs will sag to around 1.2v at 10 minutes. They will take the draw. Rechargeables will sag less but start at a slightly lower voltage. If you find a good buck driver, then it should be fine.

3. Well, some drivers you can change out one of the resistors to increase the current(Or add a variable resistance pot). Maybe start with a cheaper driver like this one and try swapping out the R2 resistor. Two drivers might also work(in parallel, this will depend on the driver, two of these drivers will work in parallel from what I have read).

4. Link.

:welcome:

Wow, thanks for the fast reply!

Those first regulators you suggested are so cheap, I'll get some and try changing R2. The second regulator you suggested has too low of a Max Vin for my 12V input.

That heat sink is exactly what I'm looking for! One thought, though, does anyone make a copper version?

-zambai

I don't think there is a copper version of that heatsink.

Besides, Al is pretty good at transferring heat(and is much cheaper). It will be fine of this project(Many lights have worked fine with less heatsinking).

According to post #29 on
http://www.cpfmarketplace.com/mp/showthread.php?t=169333
the Kaidomain driver might have stability problems if the current is increased too much.

uk_caver said:

According to post #29 on
http://www.cpfmarketplace.com/mp/showthread.php?t=169333
the Kaidomain driver might have stability problems if the current is increased too much.

Click to expand...

According to the spec sheet, too. As input voltage increases it can do higher, but 750mA is the highest recommended output at less than 12V input. The max spec at 12V is also less than 1200mA - it's roughly 1100mA according to the graph.

How about reducing a couple to 600mA each and running them in parallel?