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LEDs

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mcrites

Member
Joined
Jul 20, 2001
Location
Herndon, VA
Alright, what is the best way to insulate an LED? I keep burning mine out, you know you hear it pop and then it stops lighting up. I think it keeps shorting out, the switch is still good, I got it from allied electronics. I was wondering if there was something that I can do to make it stop grounding itself.
 

PhoenixMDM

Piano Man
Joined
Aug 21, 2001
Location
Candia, NH
I'm not exactly sure about most of ur description, but the whole popping and not coming back thing sounds familiar. On the little package ur led comes in, it says the operating voltage. Let's say your LED uses 3.7 volts, and your power source is 9 volts. To keep from shorting it, you'd have to add a resistor of the right Ohmage (i know they're ohms, but ohmage?? lol...) using this formula:

9
3.7 = -------
x

Solve for x and we get 2.432. So you would need to hook up a 2.432 ohm resistor to the negative side of the LED.

I don't usually do electrical stuff like this, so if any of you electritian-wannabes feel like fixing and correcting my work, feel free!;)
 

WillysNut

Senior Jeep Nut
Joined
Apr 18, 2001
Location
NY, USA
Heat Shrink tubing...available at most local Radio Shack's or online. Just put the right sized piece on each line before you solder or connect and then slide over the connections and heat with a lighter. You could also use a big piece around all three wires..or two..depending on the type of LED..and then heat wrap the whole package. There's better stuff out there but I'm usually too impatient to wait ! :D
 

Arkaine23

Captain Random Senior Evil
Joined
Nov 8, 2001
led question

The resistor goes on the anode side? I've got a blue led wired into a molex on the 12v line... it worked when I tested it on my car battery, but now that its in my case its not lighting. I figured one of the leads broke off or something(its in the front panel so I can't just look at it without taking the case apart), but maybe I reversed the positive/negative when I tested it on my car. It was too dark to see which side of the battery was positive and which was negative when I tested it out.

Is this right? I thought the resistor should go on the 12v wire, not the black ground wire.
 

Christoph

JAPH Senior
Joined
Oct 8, 2001
Location
Redmond, WA
If your LED's going out, that probably means that you're giving it too many volts. If there's a short, then it'll go out, but should come back on just fine when you unshort it.
 

Arkaine23

Captain Random Senior Evil
Joined
Nov 8, 2001
leds

Yeah, I'll have to pull it out and mess with it. I just got a few more led's to set up too, so I'll probably be doing that tonight.
 
OP
M

mcrites

Member
Joined
Jul 20, 2001
Location
Herndon, VA
I believe you can put the resistor on any side of the led. Is there a way that voltage can push through a resistance somehow, and kill the led? I would not think so, but I am not an electronics guru. I seem to have bad chances with LEDS :(
 

Tecumseh

Member
Joined
Feb 26, 2002
Location
Ohio
It does not matter which side you put the resistor on.
If you have the correct voltage and it doesn't light up,
you probably have the leads reversed. If you "pop"
LEDs you are probably exceeding their max rating.
This is especially true if they work for a while and
then die.

There is no substitute for measurments.
 

WillysNut

Senior Jeep Nut
Joined
Apr 18, 2001
Location
NY, USA
If your running an LED off a 12v line you need a 470 Ohm resistor to bring the voltage down to levels where your LEDs won't "pop". You can find decent 1/2 Watt ones at Radio shack or most ham radio type stores.
 

WillysNut

Senior Jeep Nut
Joined
Apr 18, 2001
Location
NY, USA
Ground to the cathode, power to the anode...this should straighten it out from a wiring perspective:
 

drunkmonkey

Member
Joined
Nov 22, 2001
Location
Blacksburg, Virginia, USA
Get out da handy-dandy voltage tester, and double check everything(you resistor, the 5v line voltage w/ the resistor on it.)
Don't be scared to put your hands in the comp while its on and test stuff.
 

aupilotxp

Member
Joined
Dec 2, 2001
Location
Danville, VA
do those tri color leds come in blue and red? thats what every light on my case is except for my baybus, which they are green and red, and i want to change the green to blue.... Possible?

Thanks

Marc
 

Arkaine23

Captain Random Senior Evil
Joined
Nov 8, 2001
resistor

running off of 12 volts, I'm using 1/2 watt 680 ohm resistors for my leds
 
OP
M

mcrites

Member
Joined
Jul 20, 2001
Location
Herndon, VA
I used a 415 ohms for my resistance. It measured at 415 ohms when I put it in line with my LED, but now it measures at 395 ohms, after the LED blew. What would cause this, or do you think I am going crazy when I measure the ohm rating? :D What I did to come to the value of 415 is:
(12V input - 3.7 forward voltage ) / .02 amps

(8.3) / .02 = 415, is this ok? And I am still boggled at the reason why it would measure 395 or so.
 

Tecumseh

Member
Joined
Feb 26, 2002
Location
Ohio
Resistors come in +-5% and +-10% usually. Your resistor
is about 5% low. This is normal. it doesn't look like you
are overloading the LED. Something else is going on.:confused:

Does/did it seem overly bright when it was working? Did
it show a steady brightness until it poped?
 
OP
M

mcrites

Member
Joined
Jul 20, 2001
Location
Herndon, VA
Yeah, it seemed to work ok. I had it my psu turned off, then I turned it back on and it popped. I dont really understand what you mean by -5% and -10%, does this mean that resistors can change values up to -10%?
 

Tecumseh

Member
Joined
Feb 26, 2002
Location
Ohio
mcrites said:
Yeah, it seemed to work ok. I had it my psu turned off, then I turned it back on and it popped. I dont really understand what you mean by -5% and -10%, does this mean that resistors can change values up to -10%?

No, they usually don't change too much over time unless
you run them hot. What it means is that they will have
a lot average at the rated value, but may be 5 or 10
percent above or below this to start with.