Laboratory Power Supply From Old ATX

I haven’t have a power supply for lab purposes for a long time ago but sometimes it would have been necessary. Besides the adjustable voltage it is also very useful to limit the output current e.g. in case of testing newly created PCBs. So I decided to make it by myself from available components.

Since I had an unused computer ATX power supply at home, I decided to use it as power source. Usually, these old ATX power supplies ends up in the trash since they have low power (relatively) and they are not usable for new computers. If you don't have one, you can easily get one very cheap from second-hand computer shops. Or just ask your friends whether they have one in the loft. These are very good power source for electrical diy projects.

This way I also don’t have to care much with the case. So I searched for a module, that fits for my expectations:

• Provides variable voltage and current
• Works from 12V input voltage
• Maximum output voltage is at least 24V
• Maximum output current is at least 3A
• And is also relatively cheap.

Step 1: ZK-4KX Module

I have found the ZK-4KX DC-DC Buck-Boost converter module that fits for all of my expectations. Above of that it is mounted with user interfaces also (display, buttons, rotary encoder) so I didn’t have to buy them separately.

It has the following parameters:

• Input voltage: 5 – 30 V
• Output voltage: 0.5 – 30 V
• Output current: 0 – 4 A
• Display resolution: 0.01 V and 0.001 A
• Price is ~ 8 – 10 $

It has many other features and protectionsFor detailed parameters and features see my video and the end of this post.

Step 2: Used Components

Above of the DC-DC converter and computer ATX modules we need only some other basic components to have a well usable power supply:

• LED + 1k resistor for indicating the status of ATX unit.
• Simple switch to power on the ATX unit.
• Banana female connectors (2 pairs)
• Aligator clip – banana plug cable.

Besides the adjustable output I also wanted to have a fix +5V output since it is used very commonly.

Step 3: ATX Power Supply

Take Care!

• Since the ATX power supply works with high voltage, take care that it is unplugged and also wait some time before take it apart! It includes some high voltage capacitors that needs some time to discharge, so don't touch the circuit for some minutes.
• Also take care during soldering that you don't make a short circuit.
• Make sure that you didn't forget to connect the protective earth cable (green-yellow) back to its position.

---

My computer ATX unit is 300W, but there are a lot of different variants, any of them is suitable for this purpose. It has different output voltage levels, they can be distinguished by the color of the wire:

• Green: We will need it to power on the device by shorting it together with ground.
• Purple: +5V Standby. We will use to to indicate the status of ATX.
• Yellow: +12V. It will be the source power of DC-DC Converter.
• Red: +5V. It will be a fix 5V output for the power supply.

And the following lines are not used, but if you need any of them, just connect its wire to the front plate.

• Grey: +5V Power Ok.
• Orange: +3.3V.
• Blue: -12V.
• White: -5V.

My ATX Power Supply also had an AC output that is not needed so I removed it. Some variants has a switch instead, which is more useful in such projects.

After disassembling I removed all unnecessary cables and the AC Output connector also.

Step 4: Front Plate

Although there is only a small remaining space inside the ATX unit, with some arrangement I was able to put the whole user interface on one side. After designing the outline of components I’ve cut the holes from the plate, using a jigsaw and a drill.

Step 5: Painting Case

Since the case looks not so nice, I bought spray paint to have a better look. I have choose metal black color for it.

Step 6: Wiring of Components

You have to connect the components in the following way inside the box:

• Power On wire (green) + ground → Switch
• Standby wire (purple) + ground → LED + 1k resistor
• +12V wire (yellow) + ground → Input of ZK-4KX Module
• Output of ZK-4KX Module → Banana female connectors
• +5V wire (red) + ground → Other banana female connectors

Since I removed the AC Output connector and there was a transformer attached on it, I had to assemble the transformer on the case with hot glue.

Step 7: Result

After assembly the case I powered it on successfully and tried every feature of the power supply.

The only thing I had to do is the calibration as you can see in the video.

Step 8: Calibration + Features

Since the measured values by the ZK-4KX Module were not the same as I measured with my multimeter, I recommend to calibrate its parameters before using the power supply. It also provides some protections against overloading the module like over voltage/current/power/temperature. The device will shut down the output if it detects any fault.

By short pressing the SW button, you can change between the following parameters to display in the second line:

• Output current [A]
• Output power [W]
• Output capacity [Ah]
• Elapsed time since power on [h]

By long pressing the SW button, you can change between the following parameters to display in the first line:

• Input voltage [V]
• Output voltage [V]
• Temperature [°C]

To enter parameter set mode, you have to long press the U/I button. You will be able to set the following parameters:

• Normally open [ON/OFF]
• Under voltage [V]
• Over voltage [V]
• Over current [A]
• Over power [W]
• Over temperature [°C]
• Overcapacity [Ah/OFF]
• Timeout [h/OFF]
• Calibration of input voltage [V]
• Calibration of output voltage [V]
• Calibration of output current [A]

Comments

[omnicarnivore]

Hi,
what precautions should be taken when doing this?

[gpavlovsky]

If you care about safety, just make a bigger enclosure which will house the *unmodified* PSU and all the extra stuff. Then you're only working with low voltages and it's much safer.

[tothmiki91]

Hi!

That's a good question, I should have include this in the description also.
- Since the ATX power supply works with high voltage, take care that it is unplugged and also wait some time before take it apart! It includes some high voltage capacitors that needs some time to discharge, so don't touch the circuit for some minutes.
- Also take care during soldering that you don't make a short circuit.
- Make sure that you didn't forget to connect the protective earth cable (green-yellow) back to its position.

[joey_turbo]

Great project. I've ben looking forward to making this. I have all the components to make this now, however the PSU I have has a large fan on top. That doesn't really leave much useable space. Well not if I want the ZK-4KX on the same side as the output posts. I may be able to move the AC input side over which could help. But it probably is easier if you do have a side mounted fan, like the PSU you have used.
I won't give up though. I need this lab power supply to complete another project.

[Gaffmaniac]

The PSU that I used has a fan in the bottom, almast as big as the case, taking up 30mm of what little space that there was to work with. I wanted to keep the fan so I ended up putting the internal circuit board in back wards (made new mounting points) relocated the AC plug to the side giving a bit more room for the other componants and still haveing plenty of cooling from the fan. The 🙂

[GirlyRobotParty]

Amazing low budget DIY project. Will build up one from my old desktop computer. Just one question: why are building in 2 sets of connectors?

[tothmiki91]

If you mean the 2 sets of banana plugs, one of them is connected to the fix 5V line, since it is commonly used by devices.
I use it a lot, but it does not have current limitation functionality. Other is the output of the DC-DC converter. Check the video for more details.

[alteregoot]

Hi there,
very nice project! Be aware though of the fact that it is no longer an approved (Tüv/KEMA etc.) device and that you should use it with the utmost caution. No insurance will cover any damage resulting from the use of these kind of devices!

I'm also looking to make some kind of adjustable power supply. To be on the safe side, I'm thinking of using a 19V laptop PS. The high voltage section then is sealed, so no worries there.
Still, it's very tempting to use a ATX-PS, as it has nice stockvoltages: 3.3V, 5V and 12V.

Thank you for your bright idea! We're living in a society that produces a lot of waste and this is a good example of recycling!

[tothmiki91]

Hi!
Thank you! :) And also the information, I didn't know that. So that's also a reason why these PSUs ends up in the trash. But anyhow, I think the insurance won't cover any damage that is caused by a self modified device. So we have to use them carefully, that's for sure!
I've been also thinking about an other power source, but the high power fixed voltages and the already available case with cooler are definitely an advatage. And this way I could keep the whole device. I also kept the removed cables, they could be very useful anytime.
I hope you will have a success building something similar!

[tytower]

Terrific . Nice use of the old ATX supply . The addition of the ZK-4KX DC-DC Buck-Boost converter module is a winner.
perhaps put a link to it .
I have a PS here and Ill build this if I get some time.

[tothmiki91]

Thank you!
If you search for "ZK-4KX" on eBay or Amazon, you will find some easily for about 10$ or less. I think it absolutely worth its price. Hope you will build it successfully!