CPU/Mobo Need help with LEDs going dim

[Eazy]

Well certain "long-life" LEDs are known to last over 300,000 hrs of use as well. But like i said voltage fluctuations, humidity and temperatures can decrease the life of a LED. So LEDs crapping out early might be a common phenomenon.

Voltage fluctuations = Have an APC UPS and a digital voltmeter on line placed next to computer. Incoming Voltage reads a steady 230 - 235v. Also have PSU voltage readouts on Desktop via Samurize - the 12v is a steady 11.98v

Humidity = Mumbai has high humidity - I have an accurate hygrometer right next to the computer and the read out now is 40%. But are not the LEDs sealed units ? Can high humidity affect them even if the units are sealed ?

Temperatures = my case temps never go over 34C - and one of the fans (which you see in picture above) is in the front panel and should not get affected by any heat inside the case. Behind this front fan are the HDD which are placed at right angle to this fan. Temps now are CPU=30C CASE=29C HDD=27C and 28C

 

[Emil]

I am commenting on some of the speculations made in this thread. From the conditions that Eazy has described, it certainly can't be the temperature. The mains voltage again is definitely ruled out because the supply to the LEDs comes from the DC output of the SMPS which is normally regulated well enough. For the same reason, Dipdude's point about "rectified and surge suppressed" is a non-starter. Humidity can be an issue because the plastic encapsulation of commercial LEDs is not hermetically sealed.

LEDs are current driven and not voltage driven. The light output is effectively proportional to the forward current. So driving an LED or a series string of them with a constant current source produces the best results. You never should connect LEDs in parallel unless they are closely matched. Otherwise the LED with the lower forward voltage will hog the current, deprive the other one, and finally fail faster. A simple substitute for a constant current source is to connect your LEDs in series and put a suitable resistor in series to limit the current. You can connect this arrangement to the 12 V DC source. The series resistor is extremely important. The value of the resistor is calculated to limit the current to about 10 mA or perhaps 20 mA. This actually depends on your LED's specifications.

As an example, if each LED has a rated forward drop of say 2 volts at 10 mA, then you connect say 5 LEDs in a series chain with a resistor of about 200 ohms. That will ensure that the LEDs last a long time.

BTW, all my advice is based on LED technology as I knew it about 7 years back before I switched over to the software industry. I don't know how much has changed since then.

 

[Emil]

As I said, I have been out of touch with the electronics field since 1998. I just did a bit of research on the LEDs available today and would like to add a point to my earlier comments.

Forward voltage drops of LEDs ranges from about 1.6-1.9V for Red LEDs to 4-5V for white and blue ones. That should give us enough of a clue to use them correctly for long life.

Never connect LEDs directly to a voltage source without proper current control.