Electronics


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Converting an ATX computer power supply to bench power supply            

 
Inside an ATX  power supply.        My power supply.                               10 watt resistor.                                                       

Normal computer power supply    I did not remove the and power socket.

There are many articles on the web on how to convert an atx computer power supply into a bench power supply. Some are simple and some are elaborate.

The one on the right has only 12vdc output as I need only a 12v supply. The wires for 3.5v and 5v output  are left inside the casing. 

One of the 5v leads is connected to a  a common lead (black wire) via a 10 ohm 10 watt cement resistor. Without this connection the power supply just shuts down. One green wire  (ground)  is  cnnected to another black wire via a toggle switch which becomes an on and off switch. Either one of the power socket can be connected to 220/230 ac.

At first I wanted to use one red and one black binding posts as as outputs but I did not have them . So I used banana plug sockets. I connected the 12v +  (yellow wire) to the red socket and a black wire to the black socket.

The unused  negative 3.5v , the negative 5v ,the negative 12v and unused black wires were cut off.

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Notes:

AC capacitor

-If you need free X2 type capacitors you can salvage them from old or dead transformerless power adaptors and dead electronic equipment that uses a capacitor power supply.  

Charged capacitor

I never expected an electrolytic capacitor inside a long dead laptop power supply/charger to hold a charge for so long.

The charger was in my junk box for a long time and I thought instead of throwing it into the garbage bin I might try to salvage one or two x2 capacitors from it. The box had no screws and i had to pry it open with a screw driver. Once opened my fingers happened to touch the terminal of a sizeable electrolytic capacitor. Instantly I got a terrible electric shock, not dangerous but it was painful.

When I shorted the terminals of the capacitor with a screw driver, a big, fat spark jumped across it. Never had I expected the capacitor able to hold its charge for so long. Well, at least I knew the capacitor was still good and worth my effort to remove it from the equipment.

I salvaged two X2 type capacitors and a voltage regulator. And as the box was still good I kept it also. As  usual not really knowing when I would use it.

As for the "shocking" experience I would always remember not to touch any high value  electrolytic capacitor when it was still in a circuit.  

Power supply to run cordless drill

Converting ATX power supply to a dc power supply

Alarm With Reed Switch 


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