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Thread: Resistor Verification

  1. #1

    Default Resistor Verification

    I’m working on my first saber build and am hoping that someone could verify the resistor values. I’m using the calculator found at http://led.linear1.org/1led.wiz but from reading quite a few threads that a "sanity check" could be beneficial. The components I have are:

    1. Li-Ion 18650 3.7V 2600mAh Battery
    2. Nano Biscotte V4
    3. Custom Tri-Cree LED (Royal Blue, Royal Blue, Amber)


    The colors/specs on the Tri-Cree LEDs are:

    Royal Blue Cree
    650mW Minimum Radiant Flux @ 350mA
    Forward Voltage @1000mA = 3.41v

    The site recommends a 2W or greater 1 ohm resistor.

    Amber Cree Part
    107 Minimum Luminous Flux @ 350mA
    Forward Voltage @1000mA = 2.65v

    The site recommends a 1.2 Watt capable or greater 1.2 ohm resistor.


    I'm also adding an accent LED for a crystal chamber and my plan is to wire it to the main LED wire. The specs for this LED is 3V, 20mA. The site recommends a 1/8W or greater 39 ohm resistor.


    Do these values sound correct?

    Thanks!

  2. #2

    Default

    For the royal blue, you could probably get away with the smallest ones in the shop, the .47 ohm .5W ones, even factoring in the higher voltage of a fully charged battery. If you have a proper heatsink it'll more than handle the brief overdriving. But the 1 ohm ones should work fine. That calculator rounds to nearest common value, so it totally skips anything below 1 ohm.

    Your others are fine. Although, and this goes for all of them, before picking resistors you really should measure the forward voltage yourself, if you can. Spec sheets aren't as accurate as you'd like.

  3. #3

    Default

    Plecter Labs has a great video on measuring forward voltage. https://www.youtube.com/watch?v=S5IICsTwTYE It does require a bench power supply.

  4. #4

    Default

    Thank you both very much for your help.

    Unfortunately, I don't have a bench power supply but am interested to what it is all about. So thank you for the suggestion and the link. I will check it out.

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