# led help



## morbidmike (Sep 11, 2009)

I dont know why but I cannot get leds to work I went to the led center and put in all the specs off the package and I go to hook them up and I'm blowing resistors and led's this cant be that complicated ...I need a good formula to figure this out I want to run 4 blinking red led's 1 blue,2 orange ,and 2 blue thanx in advance for the feed back


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## morbidmike (Sep 11, 2009)

2 green sorry


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## HalloweenRick (Nov 25, 2005)

http://led.linear1.org/led.wiz This calculator should be the guide you need. The mix of colors will be a test, but the calculator will give you the right resistor and even generate a schematic for you. But remember, Garbage In=Garbage Out.


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## niblique71 (Dec 2, 2009)

That calculator HR mentioned is great, but something else must be wrong. A few questions Mike:

Do you want them all to blink at the same time (Using one blinking led to cause the blinking)?

What is your power supply?? Volts etc.

How are you hooking them up??? Parallel or series?


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## Otaku (Dec 3, 2004)

What power source are you using? When you say the LED is blown, do you mean it won't light? Could be that you have the polarity reversed. LEDs are diodes and polarity matters. Also, are you trying to run them all off of the same supply?


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## morbidmike (Sep 11, 2009)

the led center said to use a 24v dc trans but I had 2 wall warts 12v 500 mil amp out put I used a 10mil amp resistor and it burned out it lighted barely with a 9 v battery ...Otaku it lit then went out quickly I was going to run half and half on 2 wall warts...Niblique only the red leds are blinkers the orange ,blue ,and green are just standard led's I got my supplies at radio shack but they dont have techs


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## niblique71 (Dec 2, 2009)

I should Let Otaku or Hpropman answer this but it sounds like you don't care if they blink in unisin. If that is the case, you can treat each color as a separate circuit at 12V. You can add several circuts (Different colors) to the same 12V power supply. If you want all of your LED's to blink at the same time, You'll have to get help from the more tech savy. I can tell ypou this, it should be do-able on one wall wart unless you are trying to get them all to blink at the same time with only one of your red blinking LED's


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## Otaku (Dec 3, 2004)

Let's play it safe and assume that you have 2.4V, 20mA LEDs. R-S doesn't have much in the way of specs for most of their stuff, and what specs they do have are dicey.
If you are using one LED wth your 12VDC wart (and check the output voltage - if it's not regulated it could be as high as 15-16 volts) you would need a 560 ohm resistor. If you are running multiple LEDs in series, each LED will reduce the voltage by 2.4VDC (assumed). That means if the wart is really 12VDC, you could run 4 LEDs, plus a 150 ohm resistor (you need a small buffer load in there).
The first thing you need to do is get a cheap DMM at someplace like Harbor Freight - they go for just a few bucks, and you'll use it a lot if you're going to be doing LEDs and other circuits. Check the voltage on the wart and use the appropriate resistor(s) per the LED calculator.
For blinkers, usually if you have one blinking LED in series with non-blinkers it will cause all of them to blink at the same rate. Again, use the LED wizard to determine what resistor you need for multiple LEDs wired in series.


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## Doc Doom (Aug 28, 2008)

I use this site for LED help.

http://wolfstone.halloweenhost.com/HalloweenTech/anemak_MakingLEDEyes.html#SimpleBlinkerEyes


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## morbidmike (Sep 11, 2009)

I used 2.4 leds with a 10 ohm resistor and touched it to a 500 mil amp walwart 12vdc and it smoked isnt 10 ohm bigger than 560 ohm ...like wire gauge the bigger the num the smaller the wire


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## sluggo (Jun 16, 2010)

One thing I'd like to mention because no one else ever seems to is that those calculators give you the _minimum_ resistance value needed. This is the value to use for maximum brightness. Of course, if you're using them for eyes, you rarely need maximum brightness. You may not even want maximum brightness. It is not a problem to use a larger (meaning more ohms) resistor. Personally, I never use these calculators, as I know that, given that I never use anything more than 12V, a 1K resistor is always safe with any kind of LED I might use. I buy a bag of one hundred 1K resistors for a buck from someplace like Jameco, and I'm good to go.


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## The_Caretaker (Mar 6, 2007)

Can you post a pic of the wall warts showing the specs(volt in/ volt out)


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## TheOneAndOnlyKelly (May 7, 2009)

With resistance, the higher the number, the higher the resistance, measured in Ohms (Ω). If you let too much voltage into the LED, you will fry it's little internal circuitry and it is just plastic at that point.

A single LED, assuming a forward voltage of 2.4V and a forward current of 30mA will need a 300Ω or so to prevent it from frying. I would definitely get a multimeter to check your voltages before adding your LEDs to your circuits, else you will go through a number of them. Also get a breadboard to lay everything out beforehand. That saves a lot of headaches.


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## Doc Doom (Aug 28, 2008)

morbid mike said:


> I ...and it smoked ...


Man, if I had a nickel for every time that happened to me I'd be rich.


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## morbidmike (Sep 11, 2009)

wall warts are #1120 v ac input 12vdc 500mA output...#2 120vac input 12vdc0.5a6w...leds I'm using2-green 3.0vdc20mA-40mcd.....4-5vdc 80mA-4.0mcd--blinking red....1 -5vdc -20mA-300mcd blue......and 2 yellow2.1VDC-20mA-720mcd


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## corey872 (Jan 10, 2010)

I've scanned through the posts, still not 100% sure what you want to do, but a couple of observations:

- 24v power supply is WAY tooo much. Either one of your 12V warts would work on its own.
- You mentioned a '10 mil Amp resistor' - not sure what that means, but later you said 10 ohms. That is way too small resistor for these voltages.
- Are you sure those specs are correct on the red LED? I might believe the 4-5v part, but 80mA seems excessive and especially considering a very low 4.0 mcd output. As comparison, the first specs I found on the net were 3-5V, 20mA, 3000-4000mcd. So that represents 1/4 the current and 1000x the brightness you have listed. I've listed a questionable and typical set-up below.

If you want to do it in the basic 'this almost has to work way' then you're looking at hooking 1 LED and 1 resistor in series, then hooking these series groups in parallel across your power supply. This would look like:

(+12VDC)------330 ohm resistor-----(+)green LED(-)----------(Ground)

(+12VDC)----100 ohm resistor---(+)Blinking Red LED(-)--------(Ground) (questionable)
(+12VDC)----*470* ohm resistor---(+)Blinking Red LED(-)--------(Ground) (typical)

(+12VDC)------390 ohm resistor-----(+)blue LED(-)----------(Ground)

(+12VDC)------560 ohm resistor-----(+)yellow LED(-)---------(Ground)

Other notes:
All these resistors need to be rated at 1/2 watt or more, the blinking red 100ohm resistor really needs to be 1 watt. If you are using the tiny 1/8 watt resistors from radio shack, they might smoke. If you are using lower resistances (lower ohms) than listed, they might smoke and take the LED with it. Higher resistance (higher ohms) are safe, but you will have lower light output. Blinking/flickering or otherwise 'fancy' LEDs sometimes have issues if the (-) of the LED isn't tied to ground (0V) make sure the resistor is on the (+12VDC) side. The LEDs have polarity, generally the longer lead is (+). The way I remember this is thinking "The longer lead reaches all the way to the 'ground'...but in electronics, everything is reversed, so it's positive)

You could get fancy and start putting LEDs in series, but that would require different resistor calculations and different resistors. :

(+12VDC)---270 ohm ---(+)blue LED(-)(+)yellow LED(-)------(Ground)

(+12VDC)--330 ohm --(+)yellow LED(-)(+)yellow LED(-)(+)yellow LED(-)---(Ground)

(+12VDC)---120 ohm--(+)blue LED(-)(+)blue LED(-)------(Ground)

(+12VDC)---220 ohm--(+)green LED(-)(+)green LED(-)------(Ground)

Hope this helps.


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## morbidmike (Sep 11, 2009)

thanx Cory I think this does help


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## The_Caretaker (Mar 6, 2007)

On you wall wart does it say regulated any where, if not you may be getting a voltage surge on startup, also under low loads you will be getting a higher voltage


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## morbidmike (Sep 11, 2009)

success at last thanx Corey !!!!!!

but the yellows seem to run a little hot is that normal???


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## corey872 (Jan 10, 2010)

Bit hard to say...is the resistor hot, or is it the LED? is the resistor a 1/2 watt model or something lower? Did you ever get a voltage reading of the actual wall wart? or across the actual LEDs?

This stuff is somewhat ballpark guesses based on approximations. If you can get voltage readings, that would help fine tune things.


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## morbidmike (Sep 11, 2009)

no I didnt check the voltage yet...I had all the light's on and only the yellow's resistors got warm I'm gonna leave them on for like a half hr and see what happens they will be cooled by a fan so heat build up wont be a issue hopefully..but I might bump the resistor now that I have lots of them.....all the res's are 1/2 watt


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## Otaku (Dec 3, 2004)

LEDs and/or the resistors shouldn't be running hot, it will drastically shorten the life. It's not so much that it's a fire hazard, although I've wired some LEDs incorrectly in the past and gotten a finger scorched, but you'll be replacing them more often. You really need to get a cheap DMM and check the voltage on the wart. Sounds like you're trying to dissipate a lot of wattage.


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## morbidmike (Sep 11, 2009)

I have a good DMM for work I'll check it soon and post voltage....the WW was used on my dsl modum that crapped out


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## morbidmike (Sep 11, 2009)

voltage is 18.08 vdc


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## HomeyDaClown (Oct 3, 2009)

morbid mike said:


> voltage is 18.08 vdc


Always check wall warts with a meter since they rarely match what's stamped on the label. The meter tells you exactly what voltage you are starting with. I would look for a power source that is closer to the requirements of the LEDs or no higher than 12 volts actual.

With 18 volts out you'd have to drop about 15 volts across the resistors and that always comes at a cost. With a single LED drawing 20 milliamps of current, the resistor has to dissipate about a third of a watt (Heat), too much for a 1/4 watt and would make a 1/2 watt get warm too. With more LEDs, that number grows quickly and soon starts making magic smoke appear.


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## morbidmike (Sep 11, 2009)

thanx homey!!!!!


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## thrilltainment (Apr 8, 2010)

i've written a tutorial that may or may not help on LED hookup. http://hauntforum.com/showthread.php?t=26134&highlight=HOWTO


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