LED wiring - need advice!

Update! I finally got the LM2596 module, 150 ohm resister, and the 3mm flat-top warm-white LEDs. Used my transformer's 14 volt accessory leads and the LM2596 module to get 12 volts, I installed a 150 ohm resister and then 3 LEDs in series. Everything worked, but the LEDs are very dim. What did I do wrong?

What LED's did you get?  Are these some high current LED's, or standard 20ma rated ones?  Are you sure you have 12V coming out?

You didn't buy GRJ's LED lighting module which is perfect for driving 3 series LEDs plus a 150 ohm resistor

Well, if the module's meter is reading 12.0V (DC) output voltage and you are using 3mm flat-tops so presumably not the hi-current style then I'm wondering if you're sure you have a 150 ohm resistor.

Something is certainly amiss, because 12V on three standard 20ma white LEDs with a 150ma resistor would be plenty bright.

Of course, you don' t need the resistor with my module since it's constant current.

You might if the resistor value is 150 mA

The description of the LEDs are as follows: 3mm flat top wide angle warm white LED lamp light bulb 6000 MCD FT3WW.

Used my voltmeter to verify 12 volts passed the module.

Measure the voltage across each of the 3 LEDs and then across the resistor.  They should each be about 3V when all is working.

You can also measure how much current is flowing by dividing the Voltage measured across the 150 ohm resistor by 150.  So if it is 3.0V, then current is 3/150 or 0.02 Amps (20 mA) which is expected.

Here is a photo of the resistor. The markings look correct and I read that a resister is not directional.

Having some degree of color blindness, I always checks resistors with a resistance meter.  You might try that.

I was hoping to save this picture for later, but here is the exterior light and as you can see it is very dim.

Resistor bands look like Brown-Green-YELLOW-Gold to me.  That would be 150,000 ohms (vs. 150 ohms) which would indeed make for a dim output.  YELLOW should be BROWN for 150

I'm surprised the LED's lit at all!

Two questions:  first, what would be the point of saving a picture for later posting of a dim LED; and, second, how would you have solved this problem without the assistance of stan2004 and grj?

You are correct. So the resistor bands should be brown - green - brown - gold for 150 ohms.

Well I was hoping to post a picture of the final project and the LEDs would be very bright. The answer to your second question is I would not have been able to solve this problem without their assistance. I definitely appreciate the fact that they share their knowledge and experience. It's folks like them that make this a great forum!

Right.  From Wikipedia:

http://en.wikipedia.org/wiki/Electronic_color_code

The 4th band or Gold in your resistor (5% tolerance) simply means it will be within 5% of 150 ohms.  Another common tolerance you'll see in hobby applications is 10% which is the Silver band.  Any tolerance % will work for this application.  That is, you probably can't perceive the difference in brightness between, say, 150, 165, and 135 ohms (that is, 150 ohms plus or minus 10%).

When I touched the voltmeter a crossed the leads of the LEDs, the LEDs went out. So I can assume I barely had enough voltage to power the LEDs. Thanks to all of you, I think you found the culprit. So I don't mess up again, I need 150 ohm (brown-green-brown-gold) 1/4 volt resistors. Correct?

Actually, they're 1/4W resistors, they don't have voltage ratings.   Other than that, you're correct, brown-green-brown, and the 4th color is insignificant.

Thanks everyone! Back to eBay.

Digikey is your friend for small orders.

Took a shot at redemption. Using the same power source, I put a 460 ohm resistor with a single LED and it was bright. Again, thanks for the help! I didn't notice the "k" when I ordered the resistors for the three LEDs. I'm glad it wasn't a costly mistake.

Hmm, I wonder if the Treasury Department would consider adding that "K" on to my Social Security check .

Anyway, if you have a bunch of those 460 ohm resistors, take 3 of them and put them in parallel so now you have a 153 ohm resistor which would allow you to power up your building as you plan to, take some photos to impress us, etc. etc. while you wait.

I have light! The BTS tower is almost complete. All I have to do is some minor detail work. The next step is to find a home on the layout. Thanks to everyone who helped me with the LED installation especially Gun Runner John, Stan 2004, and laid off sick!

Lookin' good, time to give it a home!