Electronics HDD LED header

Does anyone know if it's alright to connect 2 LED's in parallel to the HDD LED header on a motherboard?

I want the one in the front of my case and one elsewhere for a tiny mod I'm planning

Cheers

 

Yes, it will work fine (I do it)
Two LEDs in parallel should come out to ~40mA
The HD can handle up to ~90mA

 

Not sure I follow that, Zap. Doesn't the stock led have a series resistor or some current-limit system on the mobo? Then adding an extra led in parallel with the original will give the same current divided between the two?

 

The motherboard does have a resistor.
But remember that the resistors only takes up the Extra voltage left over.

For example:
Take a 2volt LED

+5volts----/\/\/----LED---GND

There will be 3 volts that the resistor will absorb.

BUT take the same LED and put two in parallel on one resistor

+5volts----/\/\/---+-----LED-----GND
..........................+-----LED-----GND

The two LEDs have 2 volts.. but in parallel the voltage drop will be lower (around 1.2-1.5volts) so the voltage across the resistor will increase, increasing the overall current load.

But it's nothing to worry about.

 

Thanks, I'll try it tomorrow when I get around to putting everything back together

 

I get your drift, but the V_f change isn't much at all in those circumstances (leastways, not with the Kingbright leds I usually get).



With these common Kingbright reds, V_f at 20mA is 2.0v, so a 150R resistor is spot-on at 5v supply. Add another parallel led, current through each is around 10mA, and from the chart, V_f will only have dropped to 1.9v. Put that back in the (V_s-V_f)/R equation and the total current has only gone up to 20.7mA, with each led now getting 10.35mA.

So they'll be a tad dimmer, but bright enough for case leds & no danger of blowing the HDDA electronics.

 

One transistor, one resistor, problem solved

I am planning to do this for my own case, perhaps. There are six HD LEDs on the front of the case, but I might use them for something else instead (CPU meter perhaps?). So, I was thinking I might do lots of backlit HD indicators for my 8 channel RAID (don't have 8 HDs yet though), using a transistor.

Side note: if you use several LEDs in series and their combined voltages add up to the supply voltage (e.g. six 2V LEDs in series from a 12V supply) you don't need a resistor.

MoJo

 

Well when you get 8 harddrives follow my guide here:

www.zapwizard.com/ide

 

Thanks Zap, that was basically the plan. Instead of cutting the IDE cables though, I intend to just use the spare connector as each of the 8 channels can only take one hard drive anyway.

MoJo