Mainboard LED Headers

indyjones Adventurer
Hi does anyone know how much current/voltage is, and can be supplied by the LED power and HDD headers straight from the motherboard ???
I wish to run four leds (the same ones as you get in the illuminated coolermaster fans) from the power (though this COULD be worked around) and four from the HDD.



Check your motherboard manual.
I believe it's 5-6 volts. Can't remember though.
I would guess the answer is "not much". 4 may be to much. But if you connect the diodes in serial you'll be fine. If it doesn't work it doesn't work. If you connect them in parallell you could blow the header.

(I hope this was right :D)
If you wire them in parallell the voltage drop will be the same as for one, but it will draw 4x as much current. If you do them in serial the voltage drop will be 4x as much as one, but the current the same.

(Someone please back this up, I suck at analogue electronics)
/me is still at school (uni).
/me still hasn't handed in the electronics assignments from two years ago.


I hate analogue. Give me digital and I'll do magic with it, but analogue, not gonna happen.

indyjones Adventurer
:) yeah am uni too though doing a year out doing composite engineering.

Just hoping not to blow anything fiddling around in the pc, would not be the first time :rolleyes:

indyjones Adventurer
Originally posted by Goatman
Grab a multi-meter and measure the voltage and current comming over the line.
AH but that will only say what it is supplying not what CAN be supplied. The coolermaster LEDS i plan to use when wired in series (cheers zedric for your reminding) draw 12 volts. (3 each). Now all i need is how much current can be supplied though we shall see... :rolleyes:

indyjones Adventurer
I think the answer for me is to try all for on the power LED header and see what happens for if i lose this it does not really matter as I can get the juce for running the power LEDS elsewhere. This becomes diffacult if I kill the HDD header :huh: Still I find out tomorrow. :confused:

indyjones Adventurer
Just to set things straight the mboard headed is a measly 5Volts :( so no bright led illumination from them! I have hocked 4 blue LEDS upto 12 volts using a converted fan adapter and the case I now think looks fairly funky Cheers for all your help. (I will post a picture if anybody is interested).


Way too much time here...
If you put them in series of two, the parallel those two, you will still get good brightness and at only twice the current and voltage drop. I think led have a voltage drop of .7v.


indyjones Adventurer
Originally posted by Anakist
If you put them in series of two, the parallel those two, you will still get good brightness and at only twice the current and voltage drop. I think led have a voltage drop of .7v.

I tried them in series (just 2) and they were extreamly dim. The aanswer i think is using a relay but the only relays i had to hand were 12V or ac ones.

dave holbon

OSNN Veteran Addict
Many minds have forgotten: -

LED’s until recently were not very efficient, with a small viewing angle and would fail if you connected them to a dc supply of the correct voltage the wrong way round. Modern LED’s come complete with an inbuilt resistor and in-line diode so on a computer you could connect them to both +12 and +5v without damage ail bit bright and dim. But as usual I have dimmed (permanently) these devices on even the most modern computer cases that still use unprotected LED’s (all in my experience) even though the cost difference is only 0.01 pence per device. Old hard disk drives used to have a connector to directly drive a LED, modern ones don’t using the drives motherboard controller chip as the source thereby limiting the disk drive access led to only one to save costs.

There are PCI cards (diagnostic) out there that can provide (on the front of the computer case) as very comprehensive display via led’s or even gas-discharge devices of what’s going on inside the computer but they all have one thing in common, they are expensive.

:) :) :)

indyjones Adventurer
Ok Cheers Dave, I have had to settle for the old dim style HHD LED.

Goatman i shall post a pic as soon as possible as I only have a really awful digicam (was given to me) and i need to geta new battery.

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