Power single extra LED from motherboard?

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broger22

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Apr 13, 2017
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I want to do a case mod with some acrylic, and I would like to put an LED behind it for a nice glow effect. However, I can't think of a good way of powering the LED. I do not want to have to turn on some AA battery pack every time I turn the machine on.

Any suggestions?

Thanks in advance.
 
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madmatt30

madmatt30

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You're confusing voltage & current (ampage) mate.

So no , buy the right led & it will runoff molex absolutely fine

Thing of the voltage as the supply line only & consider it can deliver variable ampage depending on what's connected.

If the led requires 12v & 0.5amp (6w) that's what itll draw from the line.

On the same way of thinking you can plug a 3kw heater into exactly the same mains socket as you would a small portable radio - does the portable radio explode in a shower of sparks ???
No it doesn't because it'll pull substantially less current from that circuit even though the voltage is the same.
 
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broger22

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Apr 13, 2017
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My confusion wasn't amps or volts. I was unaware they made LEDs that supported voltage that high. All the ones in my little plastic box are rated for 3v, and I've burnt a few with a 9v battery. Was hoping to not to have to buy anymore, but I suppose ill buy some higher rated ones.

Thanks.
 
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Ironsounds

Ironsounds

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Jul 31, 2011
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Hello... You are correct about you burning out a LED at 9 Vdc... all LED's need a current limiting resistor added... AND they have "Polarity" to them too... thus they are called a "diode" and have forward and reverse "Bias" characteristics... also Varying the current to them will also let you set the brightness of them too.

12 Vdc Automobile Blubs already have these resistors installed as part of the "Package".

Do you want to add your own resistor to your "barebones" led's or do you want to buy a "pre-packaged" option?

http://www.evilmadscientist.com/2012/resistors-for-leds/

If you give me the LED part#-spec I can show you how to choose the correct resistor for the voltage you would like to run it at B /

The correct power supply color coding is...
Black common/ground
red +5vdc
yellow +12vdc
 
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mjsaman

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Apr 9, 2017
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you can connect your LEDs in series and then connect them to molex. If you are having a 3V LED, then you should connect 4 of them in series and connect it to 12V molex. I tried few 8years back with my system and it was working sweet!
 
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madmatt30

madmatt30

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You shouldn't need a resistor to run a 3v led from a 3v line.
Just as you shouldn't need one to run a 12v led from a 12v line .
Good practice - maybe
Absolutely necessary - no.

As mjsaman mention , running a string in series can remove then need for resistors if the voltage rail is higher than necessary
If its matches you are likely good without one.
More than one led matching the supply voltage ? Wire them in parallel rather than series.
 
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Ironsounds

Ironsounds

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Hello... You haven't had any electronics training? These "Raw LED's" all have a resistor added to them in a circuit some where... theses devices are current sensitive... in the 40-20 milliamps range... if not "Biased/polarity" correctly will fail.

Parallel and series wiring can change things... but knowing how and why is simple math with the correct Diode data sheet or device characteristic curve. The resistor used is called a "current limiting resistor"... this is also a safe guard should the LED go "short", as it is also one of their failure modes.
 
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