Blown Fuse Indicator



Introduction: Blown Fuse Indicator

About: Why would i buy something ready made when i can make it myself with half the features for twice the money? DIY!

lWhen i saw this diagram online i knew it was the answer to my frustration i have with my ATX power supply. The powers supply is good, the problem is not knowing if i have blown my fuse without getting out my DMM and checking. While this is not really hard, it can be an annoying step if u have to do it several times in a row.  With this indicator i will know with just a glance if the fuse is blown or not.

I don't go into how to convert an ATX power supply. There is many to choose from here on Instructables. Such as these: . and

I apologies for my cell phone cam, it is only so good. 

This is not my diagram nor did i figure this out. I found this on line, here.

Step 1: Necessities

Be-careful. After all you are working with a power supply. 

Tools needed:

Soldering Iron
Needle nose pliers
Screw driver

Step 2: Prepare the Power Supply.

Disconnect power and remove top of power supply. Scenes i forgot to take the disassemble pics i will give a little explanation of the operation of my supply and what  diagram i am working from.

For the power supply operation the red LED indicates the mains power attached and on. The green LED indicates supply on and supplying power.

 The  diagram shows the fuse, resistor and LED and how they are positioned. That's the main portion we are interested in from this  diagram.

Diagram is from here.

Step 3: Drilling and Mounting

Drill 3 holes in the location you like. I choose in between the fuse holder and output lug. I started with an 1/8 drill bit and finished with an 5/16 which is the size of my LED holders. I don't have a vise so i held the tin cover with vise grips.

Step 4: Assemble the LED's

Take the LED, color of your liking. I chose yellow for this indicator. Make sure and install the plastic LED holder first before you solder.  
Next take the appropriate resistor for the voltage you are working on. Cut approx half of of one leg off of the resistor and solder it to the pos leg of the LED.
Next soldier the resistors now shorter leg to the neg side of the LED. I did this because of how my power supply is arranged, it will get the lengths of the legs closer to what we need to attach where we need them to go.

To determine what resistor  we need i used this calculator. . I used 1.3v forward voltage and 25mA for all 3. Only i changed the source voltage to compute. 3.3v says to use 82 ohm resistor. 5v says to use a 150 ohm resistor. 12v says to use a 470 ohm 1/2 watt resistor.

Step 5: Assembly

When soldering i try to use some kind of heat sink if possible. Note the black alligator clip. In the first pic.

We will want to solder each LED assembly with the correct resistor to the correct supply voltage fuse.
Second pic shows the 3.3v assembly is installed a soldered. The 5v assembly is installed and waiting to be soldered. The 12v assembly has not been installed yet.

Last pic shows all installed and soldered.

Step 6: Testing

First pic is with a load applied and fuse is removed to simulate a blown fuse. You see the LED is on. Indicating a blown fuse.
Second pic shows load applied and fuse installed. Led is out indicating fuse is good.
The LED's will only show an indication if there is a load or a short on the output. If fuse is blown and no load then LED will be off. 

There is many ways to skin a cat. Some better some worse, but this is how i did mine. Thanks 

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