What resistor should I use for a 1 watt bin?

[ken2400]

Just bought LE-LL011 SURE electronics
http://cgi.ebay.com/1-pcs-High-brig...ryZ36338QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

300ma 3.2-4 volts

If I had a 5volt power supply what resister value should I use?
How much current at this voltage should I be looking for? 150ma?
Thanks

 

[Gunner12]

What are you using the LED for? Also, Cree XR-E P4s are rated at a minimal of 80 lumen at a 350 mA drive current(The Q5 bins are over 100 lumen), the Seoul P4 U bins are a bit higher, the Edison opto KLC8 is also similar($4.40 shipped form DX).

Dealexteme and Kaidomain have cheaper driver in their DIY Flashlight section has a few cheap drivers.

There are also a few resistance calculators online(like this one)

 

[ken2400]

I have tried 33 ohms and now am trying 22 ohms.
I just wish they were cheaper. I did get it on Ebay for $3 so I can't complain too much.

 

[HarryN]

Here is how to make a good guesstimate.

The LED you have is a "white" so you can "guesstimate" a forward voltage of say 3.7 volts. It can vary easily from 3.5 to 4, but this is reasonably close.

5 volt supply - 3.7 volts forward voltage = 1.3 volts That is "excess" to dump.

Volts = amps x resistance

1.3 = 0.300 amps x resistance = approx 4 ohms.

Now, what power rating for the resistor ?

Power = resistance x current x current = 4 x 0.3 x 0.3 = approx 0.4 watts.

Good luck - I like resistored light setups.