Battery Configuration for 3s SST-90

[Mattaus]

Hi all,

I am doing some very early ground work for a triple SST-90 build and am wondering what my battery configuration should be.

Reading the SST-90 Datasheet seems to indicate to me that in order to drive these emitters at their full 9A potential I would need at least 3.87V across each LED. If they are configured in series like I am considering that would need at minimum 11.6V from the batteries. Assuming I use a buck converter (no driver has been chosen yet) that I'd need a couple of volts above that again.

I'm assuming then that 3 series connected 18650 cells would be inappropriate. While their fresh charge state is 4.2V each and plenty for my application, they would soon settle to 3.7V and thus my LEDs would not be driven hard enough.

Is it safe to assume therefore that I should be aiming for 4 series connected Lithium batteries for this light? I saw a triple SST-90 build not too long ago (searching for the thread now) and the modder then used 3 series connected 18650s, but was only getting 7+ amps to the LEDs.

Any suggestions would be welcomed.

Thanks.

- Matt

 

[CKOD]

For drivers, I'd definitely reccomend the der-witchtel 9A buck driver.
http://www.candlepowerforums.com/vb...icient-5A-9A-Buck-Converter-for-SST-50-SST-90

With its 22v input voltage, you should be good upto 5S Li-Ion cells. In the datasheet it states it need the input to be at least 2v higher than the output, so minimum voltage of 13.6v, which would be 3.39 V/cell for a 4S configuration, which is an acceptable ending voltage while under load.

Your LEDs will draw ~35W each, 105 watts total, or ~116W accounting for effiency of the driver. With the minimum input of 13.6v, youre looking at 8.6A (116W/13.6V) Well outside of the power range for standard (Li-Co). An IMR18650 (Li-Mn chemestry) will do the 8A, but youre looking at < 12 minutes of run time with a 1600mAh IMR cell. If you can run IMR26650 or 26500 cells You could gain capacity and run time. At 90W+ of thermal dissipation, your run time wont be limited by your batteries though, unless this isnt a handheld flashlight application.