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MasterCyclone3D

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Discussion starter · #1 ·
Hi I am wondering if any of you guys out there know what size and voltage for a LED light for HDD and Power on the case. The light seam to be real small like 2mm or 3mm I am not sure but my case is a Rosewell Blackhawk Ultra. I really don't want to bight of a LED light. but I don't know what voltage the motherboard HDD and Power can regulate.

Can you guys help me out and point out what LED light and website to used for my case. I really would like a not so bight LED. I do used my computer in the dark a lot.

I really hate the boring white and red light on this case. I am going to replace it with blue for the HDD and the pruple as UV for the power.

Will this LED light works? It said from 6v to 12v for 3mm

http://www.ebay.com/itm/12V-Wired-3-4-8-5-8-10mm-LED-Light-White-Warm-White-Red-Blue-Green-Amber-UV-Pink-/130708316747?pt=US_Lighting_Parts_and_Accessories&var=&hash=item1e6ed2a24b

Can you guys help a brother out?
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#2 ·
I think the output is 5V from the motherboard header. See,
http://www.intel.com/support/motherboards/desktop/sb/cs-009016.htm
http://www.formfactors.org/developer%5Cspecs%5Cfpio_design_guideline.pdf

But I also think there is a resistor in series to limit the current (330 ohm). So the 12V LED from Ebay you linked to aren't going to work.

LEDs work across a range of voltages. The higher the voltage across the LED's pins the more current will flow through it. More current means the LED will be brighter. Unless the supply is a constant current LED driver (which is not the case for your power light), there needs to be a resistor in the circuit. You need a resistor because LEDs have low internal resistance and you don't want a huge amount of current flowing in the circuit. Luckily the motherboard has this resistor built into it.

You need to look up the datasheet for the LED you want to use. Here are some example specs for a Red LED from Kingbright.
http://www.kingbright.com/attachments/file/psearch/000/00/00/KP-2012EC(Ver.18A).pdf
This LED works in a range of 1.7V to ~2.1V.

Knowing this you can do some maths and work out with a 2V LED, you'll get 9 mA. So pretty much any LED between 2V and 5V should work. Lower voltage LEDs equals more current. How more current translates into actual light depends on the datasheets (and your eyes, which are more sensitive to green light than blue).
 
Discussion starter · #3 ·
Quote:
Originally Posted by PassMark View Post

I think the output is 5V from the motherboard header. See,
http://www.intel.com/support/motherboards/desktop/sb/cs-009016.htm
http://www.formfactors.org/developer%5Cspecs%5Cfpio_design_guideline.pdf

But I also think there is a resistor in series to limit the current (330 ohm). So the 12V LED from Ebay you linked to aren't going to work.

LEDs work across a range of voltages. The higher the voltage across the LED's pins the more current will flow through it. More current means the LED will be brighter. Unless the supply is a constant current LED driver (which is not the case for your power light), there needs to be a resistor in the circuit. You need a resistor because LEDs have low internal resistance and you don't want a huge amount of current flowing in the circuit. Luckily the motherboard has this resistor built into it.

You need to look up the datasheet for the LED you want to use. Here are some example specs for a Red LED from Kingbright.
http://www.kingbright.com/attachments/file/psearch/000/00/00/KP-2012EC(Ver.18A).pdf
This LED works in a range of 1.7V to ~2.1V.

Knowing this you can do some maths and work out with a 2V LED, you'll get 9 mA. So pretty much any LED between 2V and 5V should work. Lower voltage LEDs equals more current. How more current translates into actual light depends on the datasheets (and your eyes, which are more sensitive to green light than blue).
Click to expand...
It said from 6v to 12 v so is that alright?
 
#4 ·
LEDs don't have a voltage that the run off of like light bulbs. All that matters is the amount of current running through them.

I'm at work and can't look at your ebay listing- does it say if there's a resistor with the LED? If so, how many ohm?
 
Discussion starter · #6 ·
#7 ·
Thanks for the information, I always thought LED use certain amount of voltage.
Quote:
Originally Posted by kevmatic View Post

LEDs don't have a voltage that the run off of like light bulbs. All that matters is the amount of current running through them.

I'm at work and can't look at your ebay listing- does it say if there's a resistor with the LED? If so, how many ohm?
Click to expand...
 
#8 ·
Ugh, I guess you could say that they do have an exact voltage.

Diodes have a specific voltage drop when they are conducting- with white LEDs, this is about 3.1 volts. So when you measure the voltage across the leds of the LED when its on, it will always be 3.1 volts. Since you can't change the voltage going through the LED, you have to set the brightness by the amount of current flowing through it. That's what I mean when I say they don't run off of a voltage- what matters is the current. You have to look at the whole circuit with LEDs.

So if you were to directly connect a white LED to a 12v supply, where does the extra 8.9 volts go? It has to be dissipated by a resistor. The resistor determines the amount of current using Ohm's law and the input voltage. If there's no resistor, there will be no limit on the current and the LED will go up in smoke from the massive current spike.

In the end, the RESISTOR determines how many volts the LED circuit needs to work, the LED itself has less influence than you might think. Like I said, its not as simple as a light bulb, which have a voltage they are designed to run at and self-regulate current.
 
#9 ·
Thanks for such detailed and informative reply.
smile.gif
I am learning lots of good thing here. Thank you everyone
smile.gif

Quote:
Originally Posted by kevmatic View Post

Ugh, I guess you could say that they do have an exact voltage.

Diodes have a specific voltage drop when they are conducting- with white LEDs, this is about 3.1 volts. So when you measure the voltage across the leds of the LED when its on, it will always be 3.1 volts. Since you can't change the voltage going through the LED, you have to set the brightness by the amount of current flowing through it. That's what I mean when I say they don't run off of a voltage- what matters is the current. You have to look at the whole circuit with LEDs.

So if you were to directly connect a white LED to a 12v supply, where does the extra 8.9 volts go? It has to be dissipated by a resistor. The resistor determines the amount of current using Ohm's law and the input voltage. If there's no resistor, there will be no limit on the current and the LED will go up in smoke from the massive current spike.

In the end, the RESISTOR determines how many volts the LED circuit needs to work, the LED itself has less influence than you might think. Like I said, its not as simple as a light bulb, which have a voltage they are designed to run at and self-regulate current.
Click to expand...
 
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