Bench Power Supply Part II  – Assembly

In the post Bench Power Supply Part I – Cabinet it was described the process of building a cabinet for the bench power supply. This second part describes the assembly of the the bench considering the electronics, sockets, wiring, AT power supply setup, working details, etc..


Frontal Assembly

The frontal assembly should be done as the image and instructions below:

  • The first 2 panels, of 5V and 12V:
    • The meter is an ammeter. In order to attach it correctly, check the points between the digits (even when the display is off it’s possible to spot them). The points should be at the bottom.
    • The first row below the meter is for the 3 switches.
    • The second row is for the 5.5mm x 2.1mm sockets.
    • The third row is for banana sockets (red on the 5V panel and yellow on the 12V one).
    • The foruth row os for the black banana sockets (ground).
  • The (VarV) Panel:
    • The meter is a voltmeter / ammeter.
    • Below the meter is the place for the potentiometer (10Ω – 10KΩ).
    • The first row, below the potentiomenter is for the 5.5mm x 2.1mm sockets.
    • The second row is for the green banana sockets (1.25V – 10V, variable).
    • The third row is for the black banana sockets (ground).
  • The left panel is for the USB sockets.


The components mounting is very simple:

  • The meters should be pushed from the ouside in until the brackets lock them on the plastic frame.
  • Switches:
    • Remove the nut and washers.
    • Push the switch screw from the inside out.
    • insert the lock washer with the tooth facing the frame.
    • Thread the nut until the switch gets tightened
  • 5.5mm x  2.1mm sockets:
    • Remove the nut and washers.
    • Push the switch screw from the inside out.
    • Insert the washer.
    • Thread the nut until the socket gets tightened.
  • Banana sockets:
    • Remove the nut and washers.
    • Push the socket from outside in.
    • Insert the washer.
    • Thread the nut until the socket gets tightened.
  • Potentiometer:
    • Remove the nut and washers.
    • Push the socket from outside in.
    • Insert the washer.
    • Thread the nut until the pot gets tightened.


Wiring Project

Before going to the wiring project itself and the soldering, it’s nice to take a look at que wiring diagrams of the meters, because they have some specific characteristics.

Voltmeter/ Ammeter

Checking the diagram below (chinese only, sorry):

It’s possible to understend some information:

  • The thin wires (red and black) are used to power the meter.
  • The thick black wire must be connected to ground.
  • The thick red wire must be connected to the positive 12V wire from the power supply, as well to the “load” (the positive tips of the sockets).
  • The thick yellow wire must be connected to the negative of the “load” (the negative tips of the sockets)



The ammeter offers 2 possibilities of wiring:


The first diagram shows how to wire the meter using a separated power supply, which means using a second power supply for this project or some sort of electrical isolation.

The scon diagram shows how to wire the meter using the same power supplay of the load.

At first, I tried to wire the meter using the second option, because I could use only one power supply. It worked fine on the 5V panel, when I wired the 12V, the meter just didn’t get on. I replaced the meter for another one but the problem was still there. Unfortunately, I could found what was going on.

So, in order to ge the bench done, I opted for the first option, using a separated (auxiliary) power supply. I have several salvage power supplies from obsolte / broke equipment, so I chose a 12V-250ma one, which is more than adequate, once the meters only use 20ma.

HOT TIP: NEVER TRASH DC power supplies of 5V-20V, because the can be very usefull on future projects.


Wiring Diagram

After some tests and experimentations, I came up with the final wiring schematics, shown on the picture below:

: This diagram was designed based on the wiring specifications of the meters I purchased. Before assembly yours, check whether the specifications of the meters you purchased are the same described here.



The soldering on sockets and switches are the done the same way on 5V and 12V panels, but is a bit different on the Variable Voltagem panel.



The + wire, comming from the meter, and the – wire (black) coming from the power supply should be soldered to the central pins on the switches. The wires comming out from the switches to the sockets should be soldered to the upper pins. As shown on the images below, the best way to do it is to peal off 2 wires, solder one of them to all the pins on the left of each switch, and the other to all the pins on the right. Solder the wires to the pins on the middle switch, cover them with some heat shrinkable tubes, then solder the wires to the other switches.



5.5mm x 2.1mm Sockets

This type of socket, in general, has 3 pins, but only 2 of them are necessary to this project (The third one is used when the socket provides energy to some device as an alternative source to a battery, for example. So, you connect the battery + to the third pin, which gets disconnected when the plug is inserted).

After some soldering try-and-error I found out the best you to connect the wires:

  • Peal off some wire.
  • Soler it to the upper pin on the switch.
  • Add some heat shrink tube.
  • Solder the wire to the pin on the 5.5mm socket.
  • Add more heat shring tube.
  • Solder the wire to the pin on the banana socket.

The first image below shows the wiring/soldering the right way:


The last image, above, for comparison reasons, shows the wrong way of doing the wiring /soldering.


Variable Voltage Panel

The wiring / soldering on the variable voltage panel is easier than the other ones, but the DC-DC Step-Down converter needs some additional work.

As the images below, the original potentiomenter on the DC-DC converter is soldered to the PCB, making impossible to access it from outside the bench.


So, it is necessary to remove it from the PCB and, in its place, solder 3 wires, to be connected to an external potentiometer.


Once done, attatch the potetiometer to panel.


Power Supplies Mount

In order to fix the power supplies to the MDF frame, use some VHB tape, which is very strong.



As I used an AT power supply as the main one, and it has a mechanical on/off switch (mine had a push-lock switch), I used the bypass socket to connect the AC chord to the auxiliary power supply. Doing like this, I only need to turn one switch on to turn both power supplies on.







Here, I list all the used components (including the ones listed in the first post  – Bench Power Supply Part I – Cabinet).

Linear Precision Potentiometer WXD3-13-2W 10K

It’s completely oversized for this project, but it is mult-turn and I had it available.

DC-DC Step-Down 4V-40V -> 1.5V-35V Converter

Excellent cost-benefit. There are plenty of other on the market, you can chose anyone you consider better or more adequate..


Used on secttions 5V and 12V.

Voltmeter - Ammeter

Used on the section Variable Voltage.


8 Sockets. They are the most standard socket type for DC power supplies.


Banana Plug Female Sockets

I suggest to purchase 8 black, 3 red (5V), 3 yellow (12V) and 2 of other color (variable voltage) – I used the green one.

USB Sockets

3 sockets. The best, in my opinion, is to use the breakout like modules.


6 Switches of 6 pins, 2 positions (Toggle Switches 6 pin 2 position or ON/OFF)


Final Thoughts

Certainly, it was the longest DIY project I was ever involved so far (years) due mostly to:

  • I took a long time do decide about my needs.
  • The shipping of the components on AliExpress, and BangGood.
  • Design, printing, testing, reprinting of the plastic frame.
  • Assembly.


  • Only one: I could have saved space using less sockets and adding an extra panel for 3.3V.

My advices:

  • Define well your needs (discuss them with other person).
  • Keep the project as simple as you can.
  • Don’t use a lot of sockets (1 of each type is probably enough). More sockets means a lot more of soldering work.
  • Understand how your components work and test them before the assemlby

On the other hand, it is one of most usefull projects I did by myself, as I can use it easily to develop electronics projects.



Fábio Lutz

Bachelor degree in Computer Science by UFRGS / Brazil; 18 years of professional experience on software development (Delphi/Pascal, Java, PHP, Javascript, ...
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