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qazwsxokmijn
02-09-2010, 07:49 PM
So I've bought some 12v prewired LEDs that connects to a molex power connector from the power. To reduce cable clutter I modded a couple so I could connect them to the 3-pin motherboard fan connector. Both power sources give 12v, but when connected to the motherboard fan connector the resistor inside the wiring gets very hot and one LED burnt and died.

Why is that? If both power sources (the molex connector and motherboard fan connector) give off 12v, why is the latter burning my LEDs?? :confused::confused::confused:

Speedy Gonzales
02-09-2010, 07:58 PM
Dont know if this will help. http://www.kpsec.freeuk.com/components/led.htm. Have a look under Calculating an LED resistor value

qazwsxokmijn
02-09-2010, 08:00 PM
Dont know if this will help. http://www.kpsec.freeuk.com/components/led.htm. Have a look under Calculating an LED resistor value
:waughh::waughh::waughh:
As you can probably tell, I am electrically-challenged.

Speedy Gonzales
02-09-2010, 08:02 PM
What are the ohms of the resistor/s you used?

qazwsxokmijn
02-09-2010, 08:09 PM
No idea. They are prewired and hidden underneath heatshrinks.

And...resistors? :waughh:

Speedy Gonzales
02-09-2010, 08:10 PM
Ok then. what are the colours on the end of the resistor/s then. If you can see them

Speedy Gonzales
02-09-2010, 08:11 PM
No idea. They are prewired and hidden underneath heatshrinks.

And...resistors? :waughh:

Well resistor then :p Change the colours here. http://www.dannyg.com/examples/res2/resistor.htm

See what it says

qazwsxokmijn
02-09-2010, 08:20 PM
Well I would tell you....but it's burnt. :p I can tell one band on one end is red though.....

KarameaDave
02-09-2010, 09:29 PM
Don't know, but maybe this is relevant.

Electrical polarity
Main article: Electrical polarity of LEDs

As with all diodes, current flows easily from p-type to n-type material.[72] However, no current flows and no light is produced if a small voltage is applied in the reverse direction. If the reverse voltage becomes large enough to exceed the breakdown voltage, a large current flows and the LED may be damaged. If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful noise diode.

http://en.wikipedia.org/wiki/Light_emitting_diode

qazwsxokmijn
02-09-2010, 10:16 PM
That quote lost me in the first sentence.....:D

Speedy Gonzales
02-09-2010, 10:17 PM
Buy an equalizer :p

qazwsxokmijn
02-09-2010, 10:40 PM
A what now??

KarameaDave
02-09-2010, 11:06 PM
A diode works in one direction, the other direction of electron flow has the potential to destroy the diode.

Paul.Cov
03-09-2010, 08:00 AM
In other words, you might have got the positive and negative terminals swapped... at a low voltage this simply results in no current flowing, and no lights. At a sufficiently high voltage things burn out instead.
If the LEDs are wired in parallel instead of in series, then this could easily by why they managed to collectively draw enough current to poke the resistors.

qazwsxokmijn
03-09-2010, 12:39 PM
I'm gonna buy some LEDs and different resistors just to toy around....anybody know where to get these things in West Auckland?

Speedy Gonzales
03-09-2010, 12:40 PM
DSE if there's one there

qazwsxokmijn
03-09-2010, 12:54 PM
I thought DSE has stopped selling that kind of stuff?

Speedy Gonzales
03-09-2010, 01:00 PM
They're still showing on their site

qazwsxokmijn
03-09-2010, 01:07 PM
Sweet, will give DSE a visit soon.