Build a Variable Lab Bench Power Supply

Working on electronic projects at the workbench, whether prototyping with a circuit, powering a small desktop device, or simply testing a component, all require a specified source of power. Using power adapters and other DC sources such as batteries won't always be enough as they're only temporary power solutions. This is where the variable Lab Bench Power Supply unit comes in being a hands-down essential apparatus to have on any maker's workbench.

With this homemade variable Power Supply unit, you can set a specific voltage (0-36V) and current limit (0-5A) for that circuit you want to power. The device even has some common fixed voltage outputs at the front as well. As a cherry on the cake, you may charge up to two Lithium-Ion cells at a time with the 2-cell automatic cut-off 18650 cell charger on the side! To top things off, all these power features internally are fully temperature regulated with the heat-activated fan seen at the top of the Power Supply Unit. Having all of these features handy, you'll be even more well-equipped in the world of hobby electronics.

Today, with this Instructable, you'll learn how to make a similar Power Supply of your own, the DIY way!

Resources:

Full circuit diagram: https://drive.google.com/file/d/1irprbFX7_oeV_-6inQfxwCJbcMkWcS6f/view

Power Supply's front and rear face blueprints: https://drive.google.com/file/d/1XNKHJ-Ro4WkKZqn6Q0eCUHvU8jWViU1o/view

MOSFET-based Temperature controlled switch - Circuit Diagram: (Credits to YT channel - ABTabi)

https://drive.google.com/file/d/1xT-7rCxKNZLwKLg-iPQoXNK4AownCvSo/view

List of Materials & Parts:

• Numerical Control DC 6-55V to 0-50V 5A Step Down Power Supply Module - https://amzn.to/3GepraP

• 180W AC to DC 100-240V AC to 36V 5A DC SMPS Step Down Converter

• LM2596 Step-Down Buck Converter - amzn.to/386B1bv

• (x2) TP4056 Single Cell Li-Ion/LiPo Charger module - amzn.to/3wzs4zq

• 5V 3A Dual USB output charging module - amzn.to/3wBp1H8

• 5V LM7805 voltage regulator - amzn.to/3PApEJF

• Temp-controlled Switch board with MOSFET & Thermistor - Homemade

• (x2) Blue LED

• (x3) Red LED

• (x1) Green LED

• IN5408 3A Rectifier Diode - amzn.to/385tGZE

• SPDT 3 pole Toggle Switch - https://amzn.to/3G5uhHn

• SPST 2 pin 10A Rocker Switch

• Banana Plugs/RCA connectors (Male & Female) - https://amzn.to/3MD8YiU

• DC Jack Connector -

• Deans/XT60 Input Battery Connector

• Alligator clips - https://amzn.to/3yNvAsZ

• DC 12V PC Fan 80mm

• PC Fan Grill

• 18650 Li-Ion 2-Cell Battery Tray - https://amzn.to/3MAhXBb

• Single Socket AC Outlet Connector

• 3-prong AC Input Connector

• 3-Wire AC Power Cord with Compatible Connector

• 14, 20, 32AWG Enameled Stranded Electrical Wire

• Perforated Prototyping boards

• 3M Shortened Philips Head Screws

• Rubber Nobs for PSU Feet (Nerf Dart Heads)

• Plywood Board 4mm

• Sheet Metal 1mm

• PSU Case (x2 CD/DVD ROM Driver Shells)

On 2 CD/DVDROM driver shells (salvaged from old PCs) we'll begin by marking out areas where we'd want certain components and parts to stick out. Afterward, we'll cut out these areas with an angle grinder, as well as some shell-adjoining tabs. A wooden or 3D-printed case may also work as the Power Supply Unit's enclosure.

Don't have an angle grinder? You may borrow one from your neighbor or instead drill sequenced holes in the shells with a drill machine until you get the desired cutouts. If you do use an angle grinder for this, safety first! Be sure to wear proper safety goggles when working with such machines. Stand a bit off to the side in case the grinder tool slips towards you.

With the cutting out of the way, we can then epoxy any areas where there are excessive grinder cuts and sand the PSU's shells for painting.

Using the color of choice (I chose marine blue), we'll spray paint both shells and any other potential parts.

With the paint being dry, let's give the bottom shell some grippy feet (I'm using nerf dart heads for their decent rubber grip).

Now, we'll first mark, then cut or drill out holes from some 4mm plywood board for parts such as the main digital power converter, toggle switch, outputs/inputs, and so on... all out of the front and rear faces of the unit which will be seated in the metal shells. Then we do the painting before mounting modules into the wooden faces. Choosing a contrasting color will really help make the overall end result stand out.

Here, we can now fixate the selected parts to be fitted into the front and rear faces of the unit. (Rear side is not shown, it contains the fitted 3-prong AC connector and AC rocker switch)

Mounting a 180W AC to DC (AC 100-240V -> DC 36V 5A) SMPS Converter along with an LM2596 (Adjustable output) Buck Converter to the base shell, we then connect them up. The smaller buck converter steps down the SMPS converter's 36V to 12V for a handful of modules within the PSU that run on that lower voltage. (The full circuit diagram is linked in the introduction).

The buck converter must be tuned to an output of 12.7V (Slightly higher than 12V) before continuing with the wiring.

Starting with the connections, hooking up switches and output ports from the board of components, we'll get the SPDT 3-pin toggle switch to toggle the DC side of the circuit from either being powered through DC input from a battery or straight from the AC-DC SMPS converter within the box.

Since we won't dive into more detail with the wiring of the Power Supply, I advise you follow the circuit diagram for fewer errors.

This 18650 battery tray here, with a few extra power modules (TP4056 Li-cell charger + LM7805 regulator), is turned into a dual battery charger, built right into the side of the unit.

With very few components, we'll make this Analog Temperature-controlled MOSFET Switch, making the 12V Fan Heat-activated, with this simple circuit hooked up to it. The circuit mainly consists of a standard N-Channel MOSFET (Electronic switch) and an NTC thermistor which is basically a resistor that varies in resistance due to a change in temperature.

The added benefit of equipping the fan with such a circuit is how quiet the Power Supply unit normally is until things inside get cooking from a heavier load. (Things though, hopefully, shouldn't get "cooking" with the fan up and running in time).

We'll mount this new DIY module on top of the heatsink of the SMPS board with the thermistor tucked into a heatsink groove, up behind the row of transistors that typically get hot when under a heavy load.

We'll hook up the 12Vdc PC Fan to the Temp-controlled Switch circuit board, after being bolted to the upper shell with its fan grill.

Finally, the last module we will mount is the Digital DC 0-50V 5A (Step Down) Variable Power Supply Module. A handy installment feature it's got is that the wire terminal block can be disconnected for ease of wiring and reconnected back into the module.

Dealing with mains power, we're wiring the AC (120V) 3-prong input connector to the AC input of the SMPS power converter board via a switch to toggle the AC power on/off. The single-port outlet at the front is also wired.

While we're at it, let's make sure that the metal case is grounded with the power input connector's ground pin, along with any other AC-related modules from around. This is a crucial step to take in order to make sure that any leakage AC currents don't zap you, but instead drain through the ground path.

Plugging the AC cord into an outlet, flicking the AC switch on, then flipping the DC toggle switch down, we have power! We should check each and every module, power output, and input for potential problems, just to check and see that all is working before closing things up.

Then, let's tune the potentiometer on the Heat-activated Fan circuit to get the fan to only start spinning when things inside start getting warm.

We'll insulate any exposed module terminals and connections within the enclosure. Hot glue should work well to do so.

With things properly insulated and fixed in place firmly, let's seat the front and back sides into the bottom shell of the unit with superglue. The upper shell of the enclosure shouldn't have to be glued for ease of removal when needed.

Let's finally slide on the upper shell, fully enclosing the unit, and securing things by bolting the shells with these 4 metal tabs. On these DVD/CD ROM shells that I salvaged, there just happened to already be 4 threaded holes on each side of the shells, this made it more convenient for bolting the two together.

The two jumper wires for the output of the Power Supply can be made using 12-18 AWG thick wire with RCA or Banana style plugs on one end, and Alligator Clips on the other end to clip onto a circuit to test.

The DIY Lab Bench Power Supply Unit/Battery Charger is now all ready for plug n' play!

To quickly run you through how this Power Supply works, it's easier than it seems.

Pressing on the "SET" button will get you to the overall list of power settings and feature controls within the digital power converter module. Under the rotary encoder knob, the "ON/OFF" button simply toggles the set power output from what's on the display. In the main menu, if you press "SET" once, then press the rotary encoder as many times as needed, you'll be able to scroll over the power settings at the top of the display, rotating the knob to change the voltage and current limit, incrementally. As you do so, you'll see the voltage in green digits changing as you rotate the knob with the output on. Seeing how much current in mA or amps a circuit/component pulls is a pretty handy feature to have too.

The total power a circuit pulls (in watts "W") is stated in the purple digits below.

The symbols on the side are indicators of things such as whether the power output is currently on or not.

The text seen at the bottom of the screen tells what the DC input voltage to the module really is.

Now that we've gotten the grips on using this Power Supply, let's finally power some things with it! The alligator clips make connecting to circuits and components really quick and effective.

Additionally, thanks to these two main specific power converters within the unit, this PSU is fully protected from short circuits and reverse polarity connections between any of the outputs. That is to say that both have the same protective features making it a secure power supply. Of course, I just had to try shorting the output leads, just for the sake of it! Another thing about the power supply that makes it unique is that with the main power converter, looking at the display, you can probe with the output leads to even measure voltage and current (Like a Voltmeter/Ammeter) just as you would on a multimeter.

With the separate fixed power outputs on the front of this PSU, you can even power certain devices and modules on the side and keep using the variable output jumper wires for powering something else.

Charging Li-Ion cells is as easy as going back to your Power Supply Unit and popping them in! No more need for separate battery charging trays when this unit is all-in-one!

These cells take around 2-3 hours until they're fully charged (4.2V), when they are finished charging, the blue LEDs turn on. In this case, each cell has its own TP4056 charging board for independent charging.

Plugging in a hefty battery pack of a voltage anywhere between 16-35V, this Power Supply pretty much gets converted into a portable one to be moved around anywhere, even away from its original source of electricity.

As you see, with things that use up a good deal of power, the heat-activated cooling fan starts spinning straight away to regulate the power transistors from within.

A piece of advice to those of you who are considering recreating this project, or making something like it, is to first think of your workbench layout and decide on what features of these mentioned you'd want to keep or add more to the power supply based on your power needs. The idea here is to get creative and be open to adjusting the design to your working environment, feel free to make a power supply like none other. A couple more things would be like building your supply in a way that you can always take the lid off, open it up to fix a certain part of it, making it more accessible.

Think of ways to protect various components that are most vulnerable to being damaged. Internally, you may support each and every module with supporting posts or brackets to make sure the entire unit can live up to the wear and tear of plugging things in and out of the ports.

With all of that in mind, you should be well set to make your own powerful little box of a machine! You shall enjoy playing around with the possibilities of what you can power with it.

You can watch my YT video tutorial for this homemade PSU at https://www.youtube.com/watch?v=7Uqy0hs1Uk8

Want to learn even more about this DIY Bench Power Supply? Check out my featured article on the official DIYODE Magazine here: https://diyodemag.com/features/project_power_diy_variable_lab_bench_power_supply

You may also want to follow me on Instagram: @max.imagination - https://www.instagram.com/max.imagination/?hl=en