LEDs and Resister markings?

[yankee flyer]

Thanks Guys for the comment's

I was gone for a few days. Had to go get some RAYS in Florida and get away from the snow and ice.

    

Lee

[rrinker]

 How many LEDs are there, are they red/green/yellow or white, and how are they wired together - all in series, all in parallel, pairs in series and each pair in paralle, etc. Figure that out and we should be able to tell if it's the 2 or .2 ohm resistor. Tolerance (4th band) will still be up in the air but if this is something that was cheap it's almost certainly 10%.

           --Randy

 

[richhotrain]

yankee flyer

Hello all.

I'm experimenting with a small string of LED lights that work off of a 3 X "AA" battery pack. They light up with 2 "AA" in series but at a lower light level than with 3 "AA".
There is a resister in the pack that is marked red, black, and gold, gold, Or It could be red, black, and silver, silver but the resister is so small I can't make it out for sure.
What voltage should these LEDs run on?

Thanks for any help.

Lee

Since you are not sure of the last two colors, here are the four possibilities:

red,black,gold,gold  2.0 ohm, 5% tolerance
red,black,silver,silver  0.2 ohm, 10% tolerance
red,black,gold,silver  2.0 ohm, 10% tolerance
red,black,silver,gold  0.2 ohm, 5% tolerance

Rich

[Hergy]

 

Thanks for the tip on DCCU. Looks like a very interesting site.

[richg1998]

Here is a link to good info on lighting. Save the link in Favorites. You will refer to it often. Check under Curriculum as there is a lot of good DCC info.

http://www.mrdccu.com/curriculum/Lighting/LED.htm

Rich

[locoi1sa]

  Lee.

 I always use a 1K 1/4 watt resister for 12 to 14 volts. This works well for loco headlights out of the decoders. If you are using them for structure lights then a wall wart thats put out around 9 to 12 volts would be enough. Always use 1 resister for each LED.

     Pete

[richg1998]

Unless you are going to put some LED's in series, say six LED's, the voltage is not an issue. LED's are current operated devices. Most have a 20 ma limit. Many people make this much more complicated than it has to be for one or two LED's in a loco.

Here are some measurements I mad a few years ago.

Measured with 12.2 VDC supply using 20 ma max current LED's. Values will vary a little depending on actual DC supply value.

I had two LED's in series. If I wanted to know the voltage drop across the LED, I would use a meter but have never had to.

Bottom line, if you work at what I call the component level, get a digital multimeter and learn how to use it. No good reason or excuse to not have a meter. They can be had for under $10.00 and will do everything a model railroader needs.

Rivet counters will insist on a $200.00 meter.

Since most here know math, figure out the cost if you misuse the meter.

Resistor Current

1000 ohm 9.0ma

750 ohm 12.45ma

680 ohm 13.12ma

510 ohm 16.25ma

And by the way, don't think of using a 1.5 volt output from a decoder for an LED. I see the question a lot. A 1.5 volt output is for, you may have guessed it, 1.5 volt bubls only.

Rich

[yankee flyer]

Duh, why didn't I think of measuring the darn thing.   
What I really wanted to do, was figure out what voltage they were running the LEDs at. the battery's measure 4.5V and the resisters value would drop that to something else. If I use them on the layout I'll need to know what voltage to supply. 

Thanks

Lee

 

[Seamonster]

But what if Lee doesn't have a multimeter?  

Here's a quick identification of resistor colours.  Your resistor is possibly a 1/8 watt resistor which is pretty darn small and hard to read.  Examine it with a magnifying glass or an Optivisor.  It should actually have 3 colour bands before the gold or silver band.  Hold it so the colour band closest to the end of the body is on your left.  Or the gold/silver band is on your right.  The 3 coloured bands represent digits and tell you the value.  The first two are digits in the value and the third one is how many more zeros to add to the end.  These are the colours:

Black = 0, brown - 1, red - 2, orange = 3, yellow = 4, green = 5, blue = 6, violet = 7, grey = 8, white = 9.

So, a 1,000 ohm resistor would be coded brown, black, red.  That is 1 followed by a zero, followed by 2 more zeros.

Hope this helps.

 

[rrinker]

 LEDs these daya are almost always 1.9-2.1 volts for the various colors, 3.2 for the white ones. Not absolute though.

 Silver and gold in a resistor are indicators of the tolerance, regular colors for the value are:

black:0

Brown:1

Red:2

Orange:3

Yellow:4

Green: 5

Blue: 6

Violet: 7

Grey: 8

White: 9

The first two bands are nmbers, the third band 10^that number time the first two dgits

Brown-black-red = 10 X 10^2 = 1000 ohms or 1k

Yellow-violet-orange = 47x10^3, 47000 or 47K

                       --Randy

[richg1998]

Get your multimeter out and measure the resistance. That is what I do hen the resistor is very small and hard to read. Works every time.

Rich

[yankee flyer]

Hello all.

I'm experimenting with a small string of LED lights that work off of a 3 X "AA" battery pack. They light up with 2 "AA" in series but at a lower light level than with 3 "AA".
There is a resister in the pack that is marked red, black, and gold, gold, Or It could be red, black, and silver, silver but the resister is so small I can't make it out for sure.
What voltage should these LEDs run on?

Thanks for any help.

Lee