Electronics 2000

Hi folks,

Well what can I say, I saw a videos on utube of some guys who have madee their own torches and I have always wondered how electronics work so thought I would try and teach myself.

I have read many many websites and understand the basics but think I may have jumped th gun a little with this project......but need to finish it so its not a waste of money...then I will take a few steps back!

Please if anyone can help me I would be soooooo greatful!!

So the project is I want to make a torch and have the following components;

Seoul P7 LED with a constant power current power supply of 2800mA. I have the hint sink and most other little bits I need such as the relector etc but....

For the power supply I have either a 14.8v battery or can buy a 9.6v battery. The website suggests using a resistor (9.6v - 2Ohms with an 18 watt power consumption), but I cant find these online and am sure I am missing something??

Although I have read the Ohms law several times I am really struggling to put it into practice.......

I think I understand that a I need to reduce the current to the LED with a resistor but not sure which one to use?

Any help anyone can give me would be absolutley brilliant! I would even consider paying for some Skype tuition if thats what it takes as i would love to crack it!!

Use this formula to calculate the resistor value: R = VR / I = (VBATT - VD) / I
R: Resistor value [ohm]
VR: Voltage across resistor [V]
I: Current in resistor and LED [A]
VBATT: Battery voltage [V]
VD: Voltage across LED [V]

Example:
VBATT = 14.8 V
I = 2450 mA = 2.450 A (chosen from datasheet. I assume this is the LED you are using: http://www.acriche.com/en/product/prd/zpowerLEDp7.asp If not please link to the correct one).
According to the "Forward Voltage vs. Forward Current" graph the current I corresponds to this VD voltage:
VD = 3.6 V
R = (VBATT - VD) / I = (14.8 - 3.6) / 2.450 = 4.57 ohm

Power dissipated in resistor is calculated like this: PR = VR * I = (VBATT - VD) * I
PR: Power in resistor [W]

Example:
PR = (VBATT - VD) * I = (14.8 - 3.6) * 2.450 = 27 W

I found this with a quick search: http://uk.rs-online.com/web/p/high-power/7028058/
but you need to find the exact one you want.

You can recalculate with other values for voltage VBATT and current I.