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LED problems 

 

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 Post subject: LED problems
Posted: Sat Dec 18, 2004 9:11 pm 
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I bought some red LED's to make a string of lights for a friend, they were 2volt 2000Mcd LED's. I used 6 of them, and added a small resistor to the positive end to compensate for voltage spikes.

I hooked them up to his car and they worked fine for about 5 minutes. Then the first in the string faded and went out, now none of them work.

What have I done wrong?

Or have I been given wrong advice from the shop?

 

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 Post subject: Re: LED problems
Posted: Sun Dec 19, 2004 2:25 am 
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ghiawar wrote:
I bought some red LED's to make a string of lights for a friend, they were 2volt 2000Mcd LED's. I used 6 of them, and added a small resistor to the positive end to compensate for voltage spikes.

I hooked them up to his car and they worked fine for about 5 minutes. Then the first in the string faded and went out, now none of them work.

What have I done wrong?

Or have I been given wrong advice from the shop?


what size resistors did you use and did you use the right ohm? ..

1/4 watt ones are not that great for cars.
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Posted: Sun Dec 19, 2004 2:43 am 
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he used the in series, thus eliminating the need for resistors. the resistor he did use would have been small, and just been there to remove voltage spikes. I guess you could have just got a dodgy led, or something along those lines, but it does seem funny that it was the forst to go. Maybe try sticking another in and see how you go?

 

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Posted: Sun Dec 19, 2004 10:01 am 
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will buy another one and give it a go. Thanks for the advice :)

 

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Posted: Sun Dec 19, 2004 3:02 pm 
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I would seriously recomend doing the whole setup again, but doing it in parallel with a resistor per led. It will give you a little more control over the cct, and it will stop the whole string dieing when a single led fails

 

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Posted: Mon Dec 20, 2004 7:34 pm 
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going parralell with LED's in a car setup is overkill, remember too, the 12V source in a car is closer to 14 volts, so if they were 2 volt LED's run 7 of them, spikes shouldnt be a problem. If you do go parralell the resisistor should be big enought that 14/R= nominal forward current of LED, so if you have a LED that wants 60mA @ 2volts you get a 2.3Kohm resistor 14/2300 = .006A = 60mA

 

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