DIY Bench Power Supply Using Old CPU

Intro: DIY Bench Power Supply Using Old CPU

Every workbench should have at least one power supply.

When you’re experimenting with electronics and microcontrollers a good power supply can be an essential piece of equipment. While you can certainly make do with USB power bricks and “battery eliminators” nothing beats having a dedicated power supply with plenty of voltage selection and current capability.

An ideal workbench power supply should have both 5-volt and 12-volt outputs, with 3.3-volts being a nice option as well. It should be capable of providing several amperes of current for each voltage.

You can buy bench power supplies of course, but they are not inexpensive. As the current capability and number of output voltages go up so does the price.

While a commercial bench power supply is certainly a worthwhile investment there is a cheaper solution that you might want to consider. Adapt an old computer power supply to use on your workbench.

Computer power supplies have all the voltages you’ll need and some very impressive current capabilities. And, thanks to mass production, they are cheap when compared to dedicated bench power supplies.

In fact, if you have access to an old computer that is on its way to the junk heap you can rescue its power supply and put together a nice bench power supply for just a few dollars.

That’s what I did actually – an old Windows desktop computer has now become a useful addition to my workshop.

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STEP 1: Cleaning the Old Power Supply

• Open the power supply with the help of screwdrivers.
• Clean the power supply from inside and outside.

STEP 2: Sorting the Power Supply Wires

• Cut all the connectors.
• Separate the different colored wires and group the wires with same colors.

• Ground – (BLACK) – The Ground or reference.
• +5 V – (RED) – Positive 5 volts.
• +12 V – (YELLOW) – Positive 12 volts.
• +3.3 V – (ORANGE) – Positive 3.3 volts.
• -12 V – (BLUE) – Negative 12 volts.
• -5 V – (WHITE) – Negative 5 volts (not on later models).
• PS-ON – (GREEN) – Power Switch On. Connect to Ground to turn on the power supply.
• PG – (GREY) – Power Good. A status voltage that is 5 volts when power is good.
• 5V Standby – (PURPLE) – Standby voltage, 5-volts at up to 2 amps. On when supply is powered up.

• Group Green and one Black wires.
• Group one Red and one Black wires.
• Group the Brown wire with Orange Wires.

STEP 3: 3D Printing

• Download the stl files.
• and 3D Print them (There are two different types of main body and front panels print any one set).
• Fusion 360 File , You can make changes in the design using Fusion 360.

STEP 4: Components Assembly

• Drill few holes using the drill machine wherever you thing is necessary .
• I have drilled 4 holes through the body and power supply to screw the power supply to the body.
• Also put the rubber foots using the screw.
• Remove the insulations from the wires tie them with zip tries.

• I covered the front panel with black textured sticker because I was not satisfied with the quality of the print (optional).

• Now add all the components(Banana Connectors, Switches and the Digital Meter) to the front panel.

STEP 5: Circuit Connections

• Make all the connections as shown in the Circuit Diagrams
• I added a aluminum heatsink to the resistor since my resistor didn't come with aluminum body.
• I added one extra AC switch which has no connections, I used it for future use.

STEP 6: Final Assembly

• Fix the Resistor and Fix the front using some screws.

STEP 7: Banana Connectors

• I made few connecting wires using some banana and alligator pins.

STEP 8: How to Use

• All Black stands for GND / -Ve
• All Red stands for Vcc / +Ve

• At the input we have to connect one of the +Ve voltage( 3V3/5V/12V)
• At the output we can connect the DC Device.
• The voltage and ampere of the device can be monitored on the digital using Output connectors.

• And rest of the pins can be used directly.

STEP 9: Problem With Initial Design

• My design includes the computer power cable and connector, the problem with this back connector design is that the power supply does not goes flat with the wall occupying some space.
• My Solution is to print the MainBodyModified.stl and connect the cable directly by removing the connectors.

Comments

[xantham]

isn't it possible to have a 24v output from an atx power supply by using the -12v and +12v's together?

[charlessuniga]

Theoretically, I would think it should work, just check two things before using it for your application:
1. Check wattage/current on each of the +12v & -12v outputs, the total (nominal of 24v) will be limited to the lower of the two outputs. Some PS’s I’ve seen as low as 100mA. Specs should be on the PS and/or listed on the manufacturer’s data sheet.
2. Anything else on that project using this same PS but another voltage output, doesn’t use the same chassis or ground connection so there’s no chance of shorting the -12v to a ground.
This can be confirmed before starting the project with a voltage meter, a jumper wire (used to “wake” or enable the PS), and a 24v rated load like a resistor (maybe 500 ohm 10 watt power resistor recommended, but you can calculate alternative options) or a small DC motor from a similar voltage sized battery drill with a brushed motor.

[Mukesh_Sankhla]

I have no idea about the +12 and -12Vs but using the Boostconverter it's possible.

[Piffpaffpoltrie]

Questions concerning the two resistors:
- What is the 8 Ohm/50 Watt resistor used for? What happens if you kick it out?
- According to your circuit diagram this resistor is loading the +5 Volt supply. 5 Volts across 8 Ohm results in a current of 625 mA and a power of about 3 Watts - I assume a 50 Watt resistor with a heat sink is a bit oversized (if at all useful).
- A 10 kOhm resistor in series with the LED is somewhat high... you have about 1 Volt across it, resulting in a current of about 0.1 mA - which is rather low for even a low-current LED (they are usually specified for about 2 mA). Perhaps this is a typo in the parts list. The series resistor I see in your picture rather looks like 1 kOhm, which is more reasonable if still a little high.

[mrbrian]

The title should maybe be PSU not CPU

[Mukesh_Sankhla]

Yes sir At first I didn't realise that and now I am unable to change it

[JurajR4]

My first idea: "Why he used old processor?" And then I click and.... ;-) Pure clickbait ;-) ...but nice project too. Like it.

[Khovet1]

Can you supply sources(amazon, banggood, aliexpress, etc) and part number/descriptions for the parts please?

[Mukesh_Sankhla]

Hello I have purchased all the components from the local stores but here are few components link from amazon.in

PGSA2Z Speaker Connector Banana Plugs Screw Type Connectors 4mm- Red & Black | Pack of 10 | https://www.amazon.in/dp/B084KT339N/ref=cm_sw_r_apan_i_19V2TWC8T95M1S4RERHG

Shockley Mini Digital Voltmeter Ammeter DC 100V 10A Panel Amp Volt Voltage Current Meter Tester Detector 0.56" Dual LED Display Auto Car (Pack of 2) https://www.amazon.in/dp/B08ZM7PJRM/ref=cm_sw_r_apan_i_7183D5KGAQQ95Q0J42CH?_encoding=UTF8&psc=1

Okayji Self Adhesive Rubber Pads for Furniture Floor Scratch Protection (Square Shape, Black) -18 Pieces https://www.amazon.in/dp/B0797SF6LD/ref=cm_sw_r_apan_i_YV8EP6W1GP44HPEW698J

Generic 2Pcs Load Resistor 50W 8ohm for Turn Signal LED https://www.amazon.in/dp/B00X73UEF8/ref=cm_sw_r_apan_i_YMH4DKX3MEBBS1MNDP15

Mini Boat Rocker Switch, Red Spst Snap in Switch Ac 250V 6A 2 Pin On/Off pack of 50 https://www.amazon.in/dp/B08RY6262W/ref=cm_sw_r_apan_i_S6PQTP7ZQ64A0KHKYQEG

NEXT GEEK Heavy-duty SPST 3 Pins ON/Off Switch 16A/250V 20A/125V AC Rocker Green Switch with Indicator Lights (PACK OF 4) https://www.amazon.in/dp/B08YX7W59V/ref=cm_sw_r_apan_i_6MFZZGJ4A8PAZJ2N9445

[alexg2020]

If you're not in a hurry, AliExpress.com you can find everything you need. Granted a lot of things are knock offs, but haven't had a problem so far. Just make sure you search under the free shipping category, that's where they get you. I'm not getting paid for promoting them, its just saving money. You get what you pay for. Good luck. In a pinch though, Amazon is the way to go. If you have prime, it's 2 day free shipping.

[Khovet1]

Yes, I have use Amazon and AliExpress numerous times. Amazon when I'm in a hurry and AliExpress and Banggood when I have the time to research out the best deals and wait for delivery. Excellent prices but it takes time. Thanks for the info. Fun hobby, no doubt.

[Khovet1]

Thank you, I appreciate your efforts.

[NirL]

This is really useful, I have a couple of these power supplies and you saved me a lot of time figuring stuff out. Thanks for sharing!

[charlessenf-gm]

"you saved me a lot of time"
Ditto

[Mukesh_Sankhla]

It's my pleasure ☺️

[mtarovsky]

How much is the weight of the printed enclosure please?

[Mukesh_Sankhla]

The 3D printed case is about 200-250gm, total weight of power supply is nearly 1Kg.