Electrical Question leds and a power source?

[Darren0330 0]

I have an electrical question … I have 8 LED’s I’m trying to install in my computer. I’m gonna glue them on to the clear side of my case. Each light runs on 2 3V batteries (cr2016) with no resistor. Now I wanna use the power from my hard drive, using scotch locks, but I don’t want to fry my harddrive… I don’t know how big of a power pack I need ?? 4AA’s 2D’s??? I would really like to use AC over DC. Any suggestions????

[tansqrx 0]

LOL consider this my good deed for the day since I don't get credit in this particular thread.

 

ok first of all before you kill yourself...

 

*I would really like to use AC over DC* - no you don't there is a reason you don't stick your finger in the wall socket. Besides everything that is running in your computer is DC. Second, LEDs will only run off DC.

 

*Each light runs on 2 3V batteries (cr2016) with no resistor* - Now this one kinda confused me. Are the LEDs you bought already wired with a battery pack or did you simply put the anaode to the + side of the battery and the cathode to the - side and it worked? I will assume the latter. The reason that you didn't need a resistor is because the battery isn't putting out enough current to fry the LED. Otherwise expect to see a very short bright flash and the smell of burning plastic, trust me I have been here before.

 

Now for the stuff you really wanted. Run down to your local Rip Off Shack, err I mean Radio Shack and get the following:

1. Computer Molex power splitter

2. Soldering Iron and solder if you don't have one

3. Blue LED's

4. Assortment of resistors (1/4 watt)

5. Shrink wrap tubing

6. Spool of 30 to 20 gage wire

 

A few basics about the power running in your case. All the power leaving the power supply is DC or direct current. The best place to tap the power is off one of the rails that supply auxiliary components, i.e. the hard drive power cables. The hard drive (HDD) power consists of four wires, two black, red, and yellow. The black wires are the ground. The yellow is +12 and the red is the +5. For our purposes we want to use the +5 or the red wire and one of the black wires. Refer to http://www.computerhope.com/help/ps.htm for more info.

 

Take the Molex splitter and cut one of the leads in the middle or near the end of the female side. Cut an approx. 1/4" piece of shrink wrap tubing and slip it over the end of yellow wire. Leave a little tubing hanging over the end. Take a lighter (if you are of the privileged class you will use a heat gun) and quickly move it around the shrink wrap. You will notice where shrink wrap gets it's name and will close up around the wire. This is actually quite an important step as if the bare wire ever comes in contact with the metal case, the power supply will short out and in the best case cause a restart. Repeat the above step for one of unused back wires. While you are at this step go ahead and strip about 1/8" of insulation off the remaining black wire and the red wire.

 

Now a little bit about LEDs. LED stands for light emitting diode as you might already know. One of the chief properties of a diode is that it acts as a one way valve for current. As such, you will have to attach the anaode (the long lead) to the + side and the cathode (the short lead) to the ground. Another peculiarity to diodes is they do not draw any current on their own (actually they do but not enough to matter here). This is why you will need a resistor in series with the LED. Figure 1 shows the proper circuit for powering a single LED.

 

 

The next question is what value of resistor to use. For this we will have to know how much current the LED needs to draw. On the back of my Rip Off Shack blue LED package I find that forward current is 20mA (.02A). We also know that the supply current is 5 volts. We then take this and plug it into the well known Ohm’s Law. Ohm’s Law states that voltage equals current multiplied by the resistance (V=I*R). We want to find the resistance so dig back into high school Algebra and rearrange the equation to find that (R=V/I). Substitute the values so that R=5/.02 => R=250 Ohms. Figure 2 shows the resulting circuit. Refer to http://forums.xisto.com/no_longer_exists/ for more help.

 

 

You have eight LEDs that you want to use so we will simply put them in parallel as shown in Figure 3.

 

 

This next part is up to artistic interpretation. I don’t know where the LEDs are going or how far apart they will be spaced or even the over all look and feel of the design so you may to choose to place the components in a different location. I will assume the back side of the LEDs will be hidden so I will put the resistor directly on the LED. Cut the leads anaode side of the LED and the resistor to an appropriate length and solder the two together. Slip a piece of shrink tubing over the bare spot and shrink. Then solder the wire to the other side of the resistor and shrink wrap. Lastly attach another wire to the ground side of the LED. This will produce a LED with two wires hanging off. Of course the length of the wire will depend on how far back to the Molex splitter they will have to travel.

 

After you have produced eight of these and placed the LEDs where you want them, gather all the positive (resistor side) wires together and solder them to the red wire that was stripped earlier. Do the same for the ground wired and solder them to the stripped black wire. See Figure 4 for a crude diagram of this.

 

 

And that’s it. With any luck you will have your LEDs shinning away when the computer comes on. If you want more there are always components you can add. For example you can put a switch in line with the positive side that will give you the ability to turn your LEDs on and off. Also you might consider putting a variable resistor (potentiometer) inline with the positive side so you can change the brightness of the LEDs. I hope this helps a little.

[qwijibow 0]

Second, LEDs will only run off DC

LED stand fr Light Emitting DIODE.
DIODE being the keyword here.

Diodes are specifically designed to handle AC.
Your computer uses them to convert AC to DC.

HOWEVER, the only AC in your computer case is mains, so you should use DC.

The reason that you didn't need a resistor is because the battery isn't putting out enough current to fry the LED. Otherwise expect to see a very short bright flash and the smell of burning plastic, trust me I have been here before.

you can buy all different types of LED's.
dont assume they are all the 1.5v variety.
he may have 6v LED's

Basically, to simplify the above, wire all your LED's in parallel, meaning all the negative legs of the LED's are wired together, and all the positive legs wired together.

Thne wire the positive rail to a RED wire from your computers poser supply, and the negative rail to a BLACK wire.

this is only 5 volts, but it should work fine.