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[vincent111]

Although im not new to the L.E.D lighting, when it comes to calculating to find the resistor needed i might as well be a n00b.

I am making a Ring of light for my xbox jewel.The clearing of the jewel has been done and the L.E.D's are in place.

The following L.E.D's are being used in a parallel current:
3x 5mm BLUE
Forward Voltage (V): 3.2 ~ 3.8
Current (uA): 30

3x 5mm WHITE
Forward Voltage (V): 3.2 ~ 3.8
Current (uA): 30

Now i have worked this calculator thing and it says i need a 10 OHM resistor which has the color code: brown black black none

Now i have a resistor here that has the same color codes except for the last one which is silver.

When i soldered it in the L.E.D's worked but got strangly warm?

My question is , is this normal or should i try and get the resistor im looking for?

This post has been edited by vincent111: Dec 2 2007, 03:18 AM

[mistformshadow]

The very last bands on a resistor indicate the tolerance. Silver is 10% and Gold is 5% (from what I can remember).
This means that in a 1,000 Ohm resistor, a Silver band means it's Max resistance is 1,100 Ohms (1.1K) and the minimum is 900 Ohms. Gold, of course, would be 1,050 and 950 Ohms.

The LED is warm because the amperage is high. It should not be HOT. If it becomes too hot to touch, then there is a problem.
The reason it is warm is because you are getting 3 milliamps(mA), rather than 30 microamps(uA).

You can get a DMM (Digital Multi-Meter) for measuring resistance, volts, and amperage for around $20 if you look in the right places. Radioshack might even offer a cheap Volt-Meter for around $12.

This post has been edited by mistformshadow: Yesterday, 04:14 AM

[zetski210]

One question, two comments:

Q1) What voltage are you trying to drive them from? (+12V, +5V, +3V3...)


C1) 30uA is a very small current for any LED, try 20mA instead:

For 12V rail, Vf = 3.8V, use a 110 Ohm, 1 Watt resistor
For 5V rail,   Vf = 3.8V, use a 16  Ohm, 1 Watt resistor

This will give you approx. 75mA though the pathway, and 25mA through each LED.


C2) I always use a separate resistor for each LED, this way you can allow for drift and/or variations in each LEDs forward voltage, and you don't need resistors with such high power ratings. Sure it takes more resistors to achieve the same job, but if you use 0603 or 0402 resistors (small surface mount type) it's not much of an issue.  (IMG:style_emoticons/default/wink.gif)