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
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
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
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
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
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.
..... Bob
Beam me up, Scotty, there's no intelligent life down here. (Captain Kirk)
I reject your reality and substitute my own. (Adam Savage)
Resistance is not futile--it is voltage divided by current.
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
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.
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
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
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
Thanks for the tip on DCCU. Looks like a very interesting site.
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% tolerancered,black,silver,silver 0.2 ohm, 10% tolerancered,black,gold,silver 2.0 ohm, 10% tolerancered,black,silver,gold 0.2 ohm, 5% tolerance
Alton Junction
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%.
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.