Resistor not charted

[frolic]

Hello, I'm another visitor from a country far, far away... that is Argentina. This is my first post in the forum but I know about it for quite a long time (more or less one year). I'm sorry for being lurking in the dark for so long. :oops:
I hope I can make it up by saying that this forum is THE source for building a lightsaber. It is so good indeed that only by searching and researching here I managed to build my own from different parts I salvaged. I promise to post a pic. :wink:
Anyway, I got to the part where one should put some light in it, so I bought a 3W LED from Prolight. The sellers specs reads:
- 90 lumens
- up to 700 mA of current
- voltage 3,55 V

I'm planning on powering it with 4AA batteries. Now, the problem is that I looked in the resistor chart in the main page and I can't find any specs that matches mine. What resistor should I use? I asked some friends who are good at electronics but they give me different answers and I don't want to risk my led.

Well, that's it. Hope you can help me. Thank you all.
Cheers

[xwingband]

Use Ohms law.

This is Voltage Drop/Amperage.

So 6V-3.55V/.7A Whatever that equals :)

Ideally you should test the LED to get that actual forward voltage OR take that one and over resistor it to be safe.

[frolic]

Thanks for your answer xwingband!
Let me see if I got this straight: according to the formula I should use a 3.5 ohm resistor, right? But what wattage?

[Ghostbat]

Thanks for your answer xwingband!
Let me see if I got this straight: according to the formula I should use a 3.5 ohm resistor, right? But what wattage?

Generally you want the big honking 3 watt resistors that look like a cinder block with wires :)

In theory you can run multiple resistors of the same value in parallel but I have had very bad luck doing so, even doubling the required wattage results in stupidly warm hardware. Take a look at the electronics kits in the store, if your resistor doesn't look like that you are running way too low.

[frolic]

Thanks for the data! So, I'll try a 3,5 ohm 3 watt resistor and then tell you how it went. Bye bye!