A computer power supply can be turned into a lab power Supply.
The cost of a computer power supply is US$30, but lab power supplies can cost as much as $100.You can save money by converting the cheap power supplies that can be found in a discarded computer.This project will give you a power supply that can produce a range of voltages, as well as some basic electronics training.It won't produce the same power as a standard lab power supply, but it will be enough for testing and running simple electronics.You can learn how to make a lab bench power supply from this wikiHow.
Step 1: Acquire an ATX computer power supply.
You can find an ATX computer power supply at your local computer store.The power supply can be removed from the case if you dismantle the computer.An additional -5 V line is included in some older ATX models.Newegg.com is one of the websites you can purchase an ATX power supply from.
Step 2: Turn off the power supply if you don't have a power cable.
Most power supply units have a power switch on the back.If you are not grounded, the remaining voltage won't flow through you to ground.
Step 3: The power supply is on the computer.
The power supply is attached to the computer case.The wires need to be removed from the computer components.The power supply needs to be removed.
Step 4: Allow the power supply to sit disconnected for a few days.
Some people suggest attaching a 10 ohmresistor between a black and red wire, however this is only guaranteed to drain the low voltage capacitors on the output - which aren't dangerous to begin with!It could cause a potentially dangerous situation.Use the power supply if you suspect it is damaged.The protection circuitry may not work if it is damaged.If the supply was connected to 120V, the protection circuits would probably have been destroyed.If that's the case, the power supply might not shut down if it gets too much.
Step 5: You need to gather the parts you need.
You will need the following items for this build.There are 6 binding posts.A power amplifier.One green and one red are recommended.2 dropping resistors.A switch.A drill and a wire cutter.
Step 6: There is a power supply unit.
The top and bottom of the case need to be removed.There are wires leading to the black caps.They can discharge a strong electric current.Any warranty you may have on the Power Supply Unit will be voided by this.Unless you have to, don't remove the circuit board.If you didn't allow the PSU to sit long enough, the traces and solder on the underside could still have high voltages on them.If you have to remove it, use a meter to check the voltage on the pins.The plastic sheet should go back under the board when you replace it.Only power supply technicians can do this.Anything over 30 microamps/volts can kill you and give you a painful shock.Before you do the conversion, make sure you remove the power cord and let the Capacitor rest for a few days.If you're not sure, use a multimeter.
Step 7: The wires need to be removed.
The plastic parts that connect to the computer's components are referred to as the connectors.You can use the wire later on for other projects if you leave a few inches of wire on the connectors.
Step 8: The wires are of the same color.
Some power supply units have additional colors.The color code for the wires is red.Yellow is +12V.Blue is -12V.The orange is + 3.3V.The power supply units that are white are older.The purple is a +5V Standby.Black is ground and Gray is power is on.Turn DC on by shorting to ground.
Step 9: The power supply unit should have a place for the parts to go.
To mark where the parts will go on the side of the power supply unit that doesn't have any fans or vents, use a permanent marker.You should mark where you want to put the binding post.You should mark where you want the LEDs, the switch and any additional components to be placed.You can either put the fan on the outside of the case or remove it.If you use a high-wattage power supply, you can attach more fans.If you don't have enough room inside the power supply, you can put all the components on a separate board.
Step 10: There are holes to be drilled in the power supply case.
To enlarge the holes until they are large enough to fit your posts, use a Dremel and a hand reamer.There are holes for the power ON and switch.Make sure the binding posts don't touch anything on the inside of the power supply.Don't leave metal in the power supply unit's circuitry.
Step 11: The holes for the lights are there.
You can use a drill to drill holes large enough for the lights to fit through.
Step 12: There are holes for the switch.
If you don't have the tools to cut a straight line through metal, you can use a drill to drill holes all along the shape of the cut you want to make.Use wire cutters to cut the space between the holes.You will need to file the edges of the hole down.
Step 13: The binding posts should be attached to the holes.
Attach the nut on the back of the binding posts with screws.Make sure they don't touch the power supply.
Step 14: The load is connected to the 10 ohm load resistors.
One red wire and one black wire should be connected to the power resistors.The power supply unit needs to function properly.The metal wall is a good place to put the power Resistor since it will give off a lot of heat.Make sure it doesn't short circuit.A lighted 12v switch will act as the load needed to turn on the power supply.If you're not afraid of soldering, you can replace the 10w power Resistor with the cooling fan that was originally inside the PSU, but be sure to match the red and black wires to each other.
Step 15: The switch must be connected.
One green wire should be connected to the end of the switch.Use a black ground wire to connect the other end of the switch.The grey and green need to be connected in order for the power supplies to work.If you don't want to use an additional switch, connect the green and black wire together.If there is a rear switch, the PSU will be controlled.Ignore the gray wire and you don't need anLED.Cut it short and keep it out of the rest.
Step 16: You need to connect the Power-OnLED.
The grey wire needs to be connected to the red one.This is the power-on light.
Step 17: The Power-On led needs to be connected to a 330 watt resistor.
The short end of the light is connected to the anode.A black ground wire needs to be connected to the dropping Resistor's cathode.Hot glue or super glue can be used to mount theLED in it's place.You can solder the wires directly to the LEDs.The wires should be covered with heat shrink tubes.The heat shrink tubes can be used to cover the resistors.
Step 18: The led should be connected.
The purple wire needs to be connected to the green one.This will be your main light.The +5V line is used for the power buttons on the board.Work.Even when the main DC outputs are off, this provides 500-1000 mA of current.If the mains are on, it might be a good idea to drive an LEDs from this.
Step 19: The 330 ohm Resistor is connected to the Standby LEDs.
The short end of the light is connected to the anode.A black ground wire needs to be connected to the Resistor's cathode.The wires should be covered with heat shrink tubes.The heat shrink tubes can be used to cover the resistors.
Step 20: Attach the white to the binding post.
Older ATX power supplies only use -5V lines.If you have a binding post, connect the white wire to it.The wires should be covered with heat shrink tubes or electrical tape.If you need -5V, look for an AT power supply with a 20-pin connection.
Step 21: The red wires have to be connected to the binding post.
The bare wire should be exposed at the ends of the red wires.Then solder them all together to the binding post.The wires should be covered with heat shrink tubing.If you only have three red wires, there is another wire that needs to be connected to them.
Step 22: The yellow wires need to be connected to the post.
The bare wire should be exposed at the ends of the yellow wires.Then solder them all together to the binding post.The wires should be covered with heat shrink tubing.
Step 23: The wires need to be connected to the binding post.
The bare wire should be exposed at the ends of the orange wires.Then solder them all together to the binding post.The wires should be covered with heat shrink tubing.A gray or brown wire may be used to represent power good or power ok.Most PSU's have a smaller orange wire that is used for 3.3V, and this wire is usually used at the connector.If this wire is not connected to the other orange wires, your lab power supply won't stay on.The orange or red wire should be used for the power supply to function.If you're in doubt, try the lower voltage.Some newer power supplies have wires that need to be connected to the actual wires for proper operation.You should have a brown wire if you only have two or less orange wires.
Step 24: The black wires need to be connected to the post.
The bare wire should be exposed at the end of the black wires.Then solder them all together to the bind post.The wires should be covered with heat shrink tubing.Pull on the loose connections.To prevent a short circuit, cover bare wire.If you don't feel like soldering nine wires together to a binding post, you can cut them at the PCB.The wires should be fine.This includes cutting wires that you don't plan on using.
Step 25: The power supply should be checked.
The power cable should be plugged into the back of the power supply.If there is a main cutoff switch, flip it.If the light comes on, it's time to check.Then flip to switch and make sure the power is on.To test the binding posts, use a digital voltmeter.Make sure you don't short any wires.It should look good and work well.
Step 26: Attach the case.
Once everything is working, you can attach the casing to the rest of the power supply unit.Most electrical testing should be sufficient for the 24v, -12), 17v and 12v that can be output by this unit.
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