3 R2 in serial - driver/buckpuck question

[barnefko]

Hi

I`building a headlamp/working light/ bicycle lamp with 3 r2's in series. My battery pack will be at 14,4V and 3Ah. I'd like to drive the leds with 750ma


already looked in:
http://www.candlepowerforums.com/vb/showthread.php?t=168471 and http://www.candlepowerforums.com/vb/showthread.php?t=196265
but didn't find my answers

As i'm living in sweden getting a good buckpuck/driver shipped from the shoppe or taskled (maxflex 35+5$) is too expensive for my project.
But i found two cheaper options:
http://www.kjell.com/filarkiv/SUPPORTPDF/81-90/87/87594/87594.pdf
The description says it's got a LM317 and needs a Vin 3V higher than Vout. this looks pretty basic to me and i don't really know if its the best i could do.

then they also got what seems a 650mA buckpuck - i asked, but they don't now either if its a buckpuck or something else
http://www.flickr.com/photos/38766567@N07/3796886719/
specs say its a 650ma , 3W led-driver with max Vin 6-12 VAC or 9-12 VDC - is this a buckpuck i can drive 3 cree R2's in series with?


OK, ordering high quality buck's and drivers from some US site is out of question because of the mostly high prices and shipping costs, which is why i started looking at DX. Does there exist a good driver solution i can order from them?

Thanks for looking at this thread.

Greetings
Bernhardt

 

[rantanplan]

Hello Bernhardt,

In case you found some free cash under your bed in the meantime ... for your application a "nflex" or "bflex" from TaskLED would be the best choice ($30+$5), a Maxflex is a boost driver (for battery voltage less than the LED voltage)

If you still want to save money and can live with one mode only, this driver from Kaidomain would be a good solution ("Kennan" replacement):

http://www.kaidomain.com/ProductDetails.aspx?ProductId=1640

It´s a buck driver, working up to 18V input and which can drive 3 XR-Es in series according to specs. User feedback on that particular driver seems to be above average too . Only minor drawback is that its output is fixed to 1000 mA, but with a steady hand and some soldering experience, changing the sense resistor(s) could fix that, I guess ... this driver costs only $4 shipped so I would order atleast two spare ones.

I would not use a "linear regulator" like a LM317. Three R2 may need around 10.5V at most, your battery pack has 16.8V when it´s fully charged .... that means up to 6V (~4.5 watt @ 750mA) are lost (turned into heat by the driver). These regulators should be used only when LED voltage and battery voltage are close together ... in other cases real boost or buck drivers are much better suited.

 

[barnefko]

Hej rantanplan

Thanx alot for this quick and straightforward answer!! Reconsidering right now to rasie the budget for my project!


Thanx alot!