correcting voltage for drop-in modded headlight?

[pulsepb]

I searched around and got some of my questions answered and tried using a led calculator but still have some confusions.

Pretty much Im trying to build a headlight for my dirtbike for night riding that will run off a battery pack.

Im using this headlight housing and replacing the upper 2 inch light with this drop-in from DX.
http://www.dealextreme.com/details.dx/sku.35242
Ill have to turn a few mils off to make it fit but it should be simple.

My question is Im using a 12v 9.8Ah battery pack i bought on ebay. The drop in module takes between 3-8.4v. I looked at adding a resistor or placing it in serial with the led running tail light to drop the voltage.

But all the material i found for wiring leds for input voltage drop were for single leds. both the headlight and taillight are multiple banks of leds so im confused if the same rules still apply.

cliff notes version:
how do i drop my 12v input down to 8.4v to run this drop in as a offroad headlight?

thanks
http://www.motorcycle-superstore.com/ProductImages/300/2010-Trail-Tech-X2-Halogen-Headlight.jpg

 

[^Gurthang]

Short answer: you want a "buck" driver circuit. It will adjust the voltage down to the correct range. Consider buying a drop-in that can handle 6V - 18V, that way you just connect it to power and you're good to go.

 

[pulsepb]

a "buck" driver will give it a constant current right? also they drop in module has some form of driver built in? how will this help my voltage drop issue?

I was looking at other drop in that accepted higher voltages however for the output i was looking at and the size i needed (ie diameter) this was my only choice.

can anyone else shed some light on my dilema?

 

[Justin Case]

Are the 5 XR-Es wired in series or parallel in this DX drop-in?

If they are in parallel, then you need a buck driver. But if you expect to deliver 1A drive current to each LED, the buck driver has to be able to deliver 5A. One choice is TaskLED's new H6CC.

If the XR-Es are in series, then you need a boost driver. Five XR-Es in series driven at 1A should have a total Vload of about 17.5V. You have an input voltage of 12V nominal. You could use a Blue Shark.

Since it appears that you have access to machine shop equipment, you can remove the existing DX driver/pill, machine a new pill to fit the replacement driver, and install the new pill.

 

[panndder]

Does anyone know if a buck driver would be needed for this? I'm hoping to run it off of 6 nimh AA's in a Maglite.