5x SSC P7 LED... constant voltage or constant current source?

I would like to make a spotlight with the following:

-5 x SSC P7 LED (900 lumens each)
http://www.dealextreme.com/details.dx/sku.12721

-on a board with heat sinks (no space limitation for now)
-using D batteries
-will be less than 4500 lumens in practice (probably around 3500 lumens)

I read that we can plug it with a constant voltage source or a constant current source.

Which one is better?

In other words: Can i plug a battery (proper voltage) on this chip or i need to buy a driver (in between).

Most definitely a constant current driver. You have not stated if you are using these 5x P7's in series or in parallel. D cells refers to only the size, not the voltage or type, so it is hard to know what is available.

Assuming in series (since I don't know of a 14Amp LED driver), the same current will go through all of them, but the overall voltage will be approximately 5x the vf of one of the LED's, or about 3.7 volts or so, for about 18.50 volts.

For any buck driver to regulate (produce the constant current), you need a higher voltage. If you had 4x LiIon D cells, you would have a max of about 21 volts, so an LED driver like this, which would provide 2.8Amps to each LED should one should work:
hipCC LED Driver ...


Needless to say this will get extremely hot, which can damage the LED's and/or the LED Driver, so depending if this will use active or passive cooling, that would limit the duty cycle of this project just due to heat.

why not direct drived?
if you dont need big runtime you can drive it direct drived with 18650 or 26500 imr

moviles said:

why not direct drived?
if you dont need big runtime you can drive it direct drived with 18650 or 26500 imr

Click to expand...

Direct drive is OK fore simple lights, but doesn't give any kind of regulation. You'll get a bright light with a fresh battery, fading as the voltage drops.

You definitely want constant current, especially with 5xP7. The large power dissipation will cause heating and a drop in forward voltage, which is definitely a problem with constant-voltage drive. Thermal runaway, here I come.

Tanks for the answers, I finally decided to try following:

100W LED
3 SLA 12V batteries

Now I only need to find the proper circuit between the LED and the batteries.

After that, I'll have to bring it 90 feet underwater but that is another challenge (the cold ocean water is an interesting fact, maybe it can replace the heat sink).