watson

iTrader: (3)

So I have a 96 SE, I put in some LED's with the 12v resistor in my guage cluster, after a couple weeks they start to blink and than they end up dying? Ive replaced them a few times thinking its a bad batch but I have tried 2 different brands.

Could cold weather be making them turn into crap??

ajm8127

iTrader: (8)

LEDs usually die from too much current. When you hook an LED across a twelve volt source, you must use a current limiting resistor to keep the current at the nominal level for the LED. What LEDs are you using and what value resistor are you using? A datasheet for the LED would be helpful.

schmellyfart

iTrader: (46)

Did you use a resistor for each LED?

watson

iTrader: (3)

Like I posted in the first post, all the LED's already have 12volt resistors in them, they are the T10 wedge style bulbs. If my gauge is pumping out more than 12 volts should I re-solder some higher voltage resistors in there?

S1cTech

Put higher resistors in there. But not to the point were it makes them dimmer.

ajm8127

iTrader: (8)

Automotive electrical systems run closer to 14 volts. Also, saying a resistor is twelve volts is like saying there are three periods in a football game. Resistors are measured in OHMS! There is a very simple relationship between the voltage supplied, the current consumed and the resistance measured. It is called Ohm's law. So you need to find out how many milliamps your LEDs need nominally. Once you have that information plug the numbers into Ohm's law.

Resistance (ohms)= Voltage (volts)/ Current (amps)

Lets say that your LEDs need 30 milliamps. That is 0.03 amps. So:

14/0.03 = 466.7 ohms

This is not a standard value, but 470 ohms is very close. Using 470 ohms, the current would come out as

14/470 = 0.02979 amps

That is plenty close enough. So if you want to find the proper resistor value, you have to know the nominal current draw of the LED. Where did you buy them?

watson

iTrader: (3)

First ones I bought from a local store, second ones I bought from ebay, I have no idea how to figure out how many milliamps my LED's need.
Here is the link to the website, if anyone can let me know which resistors I need to get that would be appreciated very much. Thanks!

http://cgi.ebay.com/ws/eBayISAPI.dll...m=290421915753

ajm8127

iTrader: (8)

Does that white piece on the bottom of the bulb pull off to reveal the resistor? If you knew the value of the resistor, assumeing a 12 volt source, you could figure out the current. Conversely, you could try contacting the manufacturer.

Also, does it seem like these get hot at all when they have been running for a while?

watson

iTrader: (3)

Yes I can pull the white piece off very easily to reveal the resistor, since the source is about 14volts than if I figure out which resistor is currently on it can I find out which one I need to swap in it?

I cant really tell if it gets hot because its behind my plastic guage piece, but I assume they do get hot.

vinny0215

i have the led wedges and they never died.. but there not as bright as the leds with the resistors.

ajm8127

iTrader: (8)

That's what I'm thinking. Can you read the color code off of it? Should be four colored bands.

watson

iTrader: (3)

So I took it apart and the resistor is blue with a red, black, black, blue and red band. Any Idea what kind I can swap it out with?

Spyguy

iTrader: (1)

That doesn't make sense. There shouldn't be that many colors.

Akiyukio

iTrader: (1)

The fifth band may be the failure rate. I not sure. I Googled a bit and found this:
http://en.wikipedia.org/wiki/Electronic_color_code

ajm8127

iTrader: (8)

Sorry, I didn't catch this post. Some resistors have five bands. With the fifth being the tolerance instead of the fourth. Some even have six, with the final band being the temperature coefficient.



Your resistor is probably red-blue-black-black-red (260 ohms +/- 2%), not red-black-black-blue-red(200,000,000 ohms +/- 2%).

12/260 = 0.045 amps

which is the expected current. Correcting for the proper voltage gives a value of

14/0.045 = 311.1 ohms.

Of course, you are not going to find a 311.1 ohm resistor, but 330 is a standard value.

14/330 = 0.042 amps.

I'm willing to bet you won't be able to tell a difference between 0.045 and 0.042 amps visually.

cashoit

Yeah man if LEDs keep dyin try a higher rated resistor...LEDs dont require much current

jwsmith

ajm8127 has already deeply answered and explained watson's problem. Why did you repeat that simple little statement?

I predicted forurms.maxima.org to be nothing but experienced hands-on maintenace workers to be assisting each other. After reading post 16 it looks like some people are just copying or repeating.

watson

iTrader: (3)

Thanks a bunch ajm8127, you definately are the electronics guru.
So all I have to do is go buy some 330ohm resistors abd solder them in?

ajm8127

iTrader: (8)

I had another thought: it may not be the LEDs dying at all. Power dissipation is another very important aspect to consider when designing a circuit. In your case, 42 milliamps at 14 volts would dissipate a total power of 0.588 watts (14 * 0.042) This becomes important when you notice that resistors are rated in watts as well as ohms. Now this value exceeds half a watt, but is very close. You may be able to get away with a half watt resistor here, but usually you want to exceed the actual power dissipation when specifying a part.

330 ohm 1/2 watt: http://search.digikey.com/scripts/Dk...6690&k=330H-ND

330 ohm 1 watt: http://search.digikey.com/scripts/Dk...e=P330W-1BK-ND

In this case, the resistors are approximately the same size, so that doesn't come into play. Thus, the one watt resistor would be the way to go.

You could also try 390 ohms. In which case this one would be good: http://search.digikey.com/scripts/Dk...e=P390W-1BK-ND

The reason that I included the 390 ohm one this time is that it is possible that your LEDs are being over driven to get more light out of them. You always have to give something up as you gain something else, and in this case you sacrifice life for brightness. Using a 390 ohm resistor at 14 volts would give you 36 miliamps and 0.5 watts. Are your LEDs actually being over driven? It's impossible to tell unless you can figure out which LEDs you have, then we can look up that datasheet.

I would buy both and experiment. They are cheap. Even if you buy ten that you don't use, that's only $1.72 that you wasted.

Here is a comparison of a 1/4 watt and a 1/2 watt resistor for reference so you can try to figure out what value came with your LEDs:

I don't have any of those one watt resistors to take a picture of, but, according to their datasheet, they are the same size as the 1/2 watt one above.