Resistor Calculation check and advice needed

[Count Voodoo]

Hello, I am putting together my first build with the Graflex 2.0 and I am figuring out which resistors I will need for the Cree Tri-XP-E2 RB/RB/W. I have done some research and used this LED calculator online. http://led.linear1.org/1led.wiz I just wanted to run the results by you seasoned veterans and seek some advice. I am hoping to obtain a NB V3 board powered by a 3.7 18650, I am using a 3d Printed chassis from Darth Ryo. With that said here are the specs.

Royal Blue Cree Part# XPEBRY-L1-0000-00Q01
600mW Minimum Radiant Flux @ 350mA
Forward Voltage @1000mA = 3.41v
Calculating = 1 ohms, 1/4W Resistor

And

White Cree Part# XPEBWT-L1-0000-00F51
266 Minimum Luminous Flux @ 1000mA
Forward Voltage @1000mA = 3.15v
Calculating = 1 ohms, 2W Resistor
Depending on if this is correct, I have seen the 1 Ohms,2W resistors, but for the 1 ohms, 1/4 W what would I use?

Thanks for any advice, sorry if its a silly noob question, I really am trying to do my due diligence so I dont have to bother everyone!

voodoo

[NanoRex]

You should also do the calculation manually to see if it's correct. The calculator you used seems to have done some generous rounding, and I think you punched in some incorrect values because you should be using a much higher wattage resistor for your main dice.

[Greenie]

Hello there. Welcome to the forums. Those values seem a little high. Sure, they'll do the job but the bigger the resistor value, the dimmer your LEDs will be. I calculate the rB @ 0.29ohms and the W @ 0.55ohms. I know there is a 0.47ohm in store, good for the rB, not sure about the closest to 0.55.
Hope your build goes well. MTFBWY :mrgreen:

[FenixFire]

Ran your values through the same calculator as it is the same one I use for double checking when building prototypes. I got 1 ohm 2w for both green and r-blue. But as mentioned above the algorithm the calculator runs rounds to the nearest most commonly available resistor size, usually to the full or 1/2 ohms and 1/4, 1/2, or whole watts.

Edit: Just realized you had the blue @ 350mA not the max...so yeah it does give 1 ohm 1/4 watt.

[Count Voodoo]

I am trying to do this manual without a calculator and I am a bit confused. So R= U/I, making for the RB LED for example R=3.7-3.41 / I. I am so new to this and its probably right there in front of me but where am I getting the I value to finish the equation?

Fenix- The 350mA was just what was listed on the product info, should I be using a different number for this if it is not the max? should I figure at 1000 like the RB? Sorry, trying to figure all this out haha

[darth_chasm]

The 350mA is in reference to radiant flux measurement. You only need to be concerned with forward voltage and the max current rating of 1000mA.

because we deal with 1000mA (all Cree colors), you can simply just subtract the forward voltage from the battery voltage and that will give you your requirements.

[Count Voodoo]

Awesome that makes it a lot easier! So now I just find a Resistor which is equal or greater to that result, preferable as close to the value as possible so I can have the smallest resister possible to keep the force strong in the led

[darth_chasm]

Yep. Greenie had it there all along ;)

[Forgetful Jedi Knight]

I'll leave this here:

http://forums.thecustomsabershop.com/showthread.php?17109-Tutorial-FJK-s-quot-Down-and-Dirty-quot-guide-to-Ohm-s-Law

[Count Voodoo]

Yep. Greenie had it there all along ;)

Oh yes! I was just trying to figure out how he did it! All the help got me there and I really appreciate it. I didnt know the general (I) values to LED's and colors so I was kind of confused.
I'll leave this here:

http://forums.thecustomsabershop.com/showthread.php?17109-Tutorial-FJK-s-quot-Down-and-Dirty-quot-guide-to-Ohm-s-Law

Thanks that helped big time, I did the formula for myself to make it make sense and the info there really helped.

<R>(ohms)= Vfbattery - VfLed / I

<P>(Watts)= R* (I^2)

Royal Blue
(R)= 3.7v - 3.41v / 1A = .29
(P)=.29 * (1)^2= .29
I did the whole equation on RB just to burn it in. Guess when (I) = 1A I can do it the easy way in the future.

Thanks a lot guys!

[FenixFire]

I'll leave this here:

http://forums.thecustomsabershop.com/showthread.php?17109-Tutorial-FJK-s-quot-Down-and-Dirty-quot-guide-to-Ohm-s-Law

Thanks, I was looking for that link for him...I book marked it on the Ipad but not the computer unfortunately.

[Count Voodoo]

Should I just go with the 1 ohm 2W resister for the .55 the white LED requires or do you think I could find better? I definitely want it as bright as possible. It is just for FoC, so im not sure it makes a big difference.

[Forgetful Jedi Knight]

Should I just go with the 1 ohm 2W resister for the .55 the white LED requires or do you think I could find better? I definitely want it as bright as possible. It is just for FoC, so im not sure it makes a big difference.

That will be fine, as you said, it won't make a huge difference.

[Count Voodoo]

it looks like the 1ohm 2W's are out of stock. If I try to track down some 1 Ohm 1W online for the .55 ohm, is there a specific brand I should look for? Material? just wondering if a resistor is a resistor is a resistor haha

[Forgetful Jedi Knight]

Usually carbon film tend to be the best.

[Count Voodoo]

I ordered some resistors but i just want to double check the Royal blue. I found 1 ohm 1 W for the white which will be fine, but the RB was only .29 so I was able to find some .39 ohm, 1/2 w. Will that be cutting it too close for the blue or will I be ok?

[darth_chasm]

That'll be just fine. Equal to or greater than is the rule.

[Count Voodoo]

Ok awesome thanks!