Introduction: Portable Variable Voltage Power Supply

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About: Old timer ... Still learning

This is my very first Instructable, in fact the very first time that I am writing online about my hobby.

As an electronics hobbyist, I have made many small projects. The process involves finding an interesting circuit, testing it out on a breadboard, finalizing it, designing a PCB for it, getting together all the components, and then mounting them on the PCB and testing. I use Cadsoft Eagle to design the layout freehand for perfboard (0.1" hole spacing) - similar to Veroboard, but with individual pads for each hole instead of copper strips connecting the rows of holes together. I may make an Instructable if anyone is interested in the process - it's a lot less messy than PCB etching.

The reason for the long explanation above is that a few months ago I came across these ready assembled modules on the AliExpress website, which save all the above processes for some projects. All you need to do is decide how you want to connect them together.

One of my first projects using these modules was this portable variable voltage power supply. It features a choice of two types of charging input sockets, a 5V USB Socket and a 3.93V to 19.2V variable DC Output with an LED Panel Volt Meter to read the output voltage.

Step 1: The Components

The Part List
The modules used in this Instructable are shown in the top picture above.

The module names and the other required components are listed below:

  • 1 pc - 2.5-30V Red LED Panel Voltage Meter
  • 1 pc - TP4056 Charger Module
  • 1 pc - DC-DC 5V Booster Module
  • 1 pc - LM2577 or XL6009 DCDC Booster
  • 1 pc - Potentiometer 20K
  • 1 pc - 27K Resistor
  • 1 pc - Power On/Off Switch
  • 1 pc - 1N5819 Schottky Barrier Diode (See text)
  • 1 pc - DC Jack Socket (yellow) for 5V input (See text)
  • 1 pc - Lithium Battery (See text)
  • Case, Knob, Screws, Plastic Pillars, Plastic Nuts, etc

Additional Notes on Modules
All the modules were purchased online from AliExpress (http://www.aliexpress.com/). Here is the list and prices that I paid (per lot ... not per piece!):

  • Mini DC 2.5-30V Red LED Panel Voltage Meter (5 pcs) - $ 5.50
  • TP4056 Charger Module + DC-DC 5V Booster module (5 sets - 1 + 1 pc per set) - $ 4.80
  • LM2577 or XL6009 DCDC booster (5 pcs) - $ 6.60
  • Potentiometer 20K B20K 15mm (10 pcs) - $ 4.88

All the prices are in USD, free shipping. Some prices may have changed now, since these modules were purchased around the beginning of this year.

A NOTE ON THE TP4056 CHARGER MODULE: The module that I used in the construction is not the same as the one in the picture above. The last batch that I ordered was for the Micro-USB version instead of Mini-USB that I got previously. They are identical except for the socket and the Green LED, which is replaced with a Blue LED. I didn't have an unused original one at hand when taking the picture.

A NOTE ON THE DC-DC BOOSTER: There are two types of modules available. They look almost the same, but one is a booster (the one we are using here boosts the voltage from 3.7V up to around 40V+) and the other is a step down voltage regulator (it reduces the input voltage and regulates it ... like a 3-terminal voltage regulator but without the heating issues). More details on how to identify them are provided in the picture above. To ensure that you will get the correct one, search AliExpress for "LM2577 XL6009 voltage booster".

The Voltage Adjust Pot
The 20K Pot together with the 27K Resistor replace the 50K preset on the DC-DC Booster module. I replaced the preset for the following reasons:

  1. It was originally wired so that the output voltage decreased when you turned it clockwise. You would expect it to increase.
  2. I thought it would be better to have a knob instead of a screwdriver slot.

  3. The maximum rating for the panel meter is 30V. With the 3.7V battery, the DC-DC Booster outputs more than 40V at the maximum end of the preset. I actually need up to 18V for normal use, so I calculated the Pot / Resistor value for a maximum of around 20V. You can change the maximum voltage by adjusting the value of the Pot / Resistor combination (maintaining the total of around 50K), but if you are using the same LED panel meter that I have used, you have to limit the maximum to 30V, otherwise the meter will be damaged. With This DC-DC Booster, the minimum voltage will always be more than the battery voltage i.e. you won't be able to go below around 3.9V.

A NOTE ON REMOVING THE PRESET: Desoldering components from a double sided PCB is not as easy as from a single sided board. You have to be very careful not to damage the tracks on both sides and also the through-holes.

The best way to start is to apply solder to each of the points first. The additional flux will help the original solder to flow. Then lay the bit of the soldering iron across all three solder points at the same time and gently ease the preset out. The job will be easier if you hold the PCB width-wise, components downward in a vice.

To clear the solder from the through-holes after the preset is removed, with the PCB still in the vice, hold your solder-sucker and soldering iron on opposite side of each hole. When the solder melts, you can suck it cleanly out (or maybe in two or three attempts!). Melting more solder over the hole releases more flux and helps the solder flow better.

If you don't have a solder sucker, the other alternative is a bamboo toothpick. Sharpen the tip of the toothpick so that it is a bit narrower. Hold the soldering iron tip on one side of the hole and push the toothpick through from the other side when the solder starts melting. The bamboo takes the heat well and also does a good job of cleaning out the hole. Toothpicks made of other, softer wood may crumble or burn.

The Power Switch
The Power Switch is just a normal SPST (Single Pole Single Throw) toggle switch.

The 5V DC Jack Socket
The DC Jack and the diode are optional. I added them in so that I could have two options for charging the battery. This is mainly because I always have a 5V adaptor with the yellow plug on my workbench, but I can never find the correct USB cable when I need it!

Please note that you should only use one of the two charging inputs for charging. Never both together. The diode, if you are using it, can be replaced by the normal 1N4000 series.

The Lithium Battery
We finally come to the Lithium battery ... the reason that I decided on this project. I rescued it from a portable phone-charger that was headed for the bin. The charger was dead, but when I checked the battery on my Charger Module, I was able to charge it, and it maintained the charge. A few months later it is still alive and working for me.

Step 2: The Schematic / Layout

Wiring the Components Together
The interconnectivity of the various components is quite straightforward and should not be much of a problem even for beginners. The only skill you need is soldering.

I have included a picture of the actual wiring for reference. Please note that you will not see the Power Supply Terminal block in the physical layout since it is located under the main DC-DC Booster.

Notes on the 5V DC Booster
It was an afterthought. I figured, I already had the battery and it would be nice to have a fixed 5V source to use for breadboarding or charging my phone.

In order to accommodate it, I had to re-do the whole lower part of the casing. I also had to remount the USB Connector on the module vertically, so that it would be available on the front panel. Please see the diagram.

Step 3: The Casing and Finishing

The Casing
The size of the casing was determined by the size of the largest component, the battery.

We have some very neat square plastic casings available in our local market. The one I used is available in black and white. The size is 110mm x 110mm x 24mm. I thought the white went very nicely with this project. This casing has a battery compartment to hold four AA batteries, which I repurposed to hold some of the electronics.

Mounting the Components in the Casing
The battery is stuck to the inside of the lower casing using double-sided tape (same as in the original unit that it came from).

The measuring and cutting of the square holes was done using very basic tools - An L-Angle, a 6" steel ruler, a cheap plastic Vernier calliper, a handheld mini-drill (also made by me) and a set of needle files.

You will notice that there are no mounting screws anywhere on the outside of the casing. The modules are all mounted with steel screws on 3 mm threaded plastic pillars or plastic nuts (depending on the height required), superglued to the inside of the upper casing. I have included some pictures of the mechanical parts for reference.

To keep this Instructable short, I have not included the casing construction, or how I get the Red and Green Charging LEDs to come out at one point on the front panel. If there is any interest in this, I can include it all in another Instructable.

Step 4: Conclusion

Some Uses for your Portable Power Supply
The fixed 5V and the variable voltage share a common ground point, so this unit is very useful when I need more than one voltage to power a breadboard project.

When it is not convenient to move the job that you are working on to the power supply on your workbench e.g. a gadget or an interior lamp in your car or the LED replacement halogen lamps in your kitchen, all you do is adjust your portable power supply to the correct voltage and work on location.

Coupled with four super bright white LEDs wired series/parallel (for 6V drive) on a 1/2" square PCB, it is very useful for working in dark corners. You position the power supply at a convenient place while you adjust the direction of the light. The stiff wires that connect the LED PCB to the power supply hold the light steady while you work hands-free ... Now you can see what goes on in those dark corners of your cupboard!

More details on the Battery
The TP4056 Charger Module is designed to charge lithium-ion (Li-ion) batteries only. You can't charge Nickel Cadmium (NiCd), Nickel Metal Hydride (NiMH) or Lead Acid batteries with it.

I have tried charging all kinds of Li-ion batteries including mobile phone and camera batteries with the Charger Module. As long as the rating is 3.7V and you correctly connect the +Ve and -Ve terminals of the battery to the Charger, it will charge. However, as a precaution, when charging a battery for the first time, I would recommend being around during the charging and checking the battery (with your finger) occasionally. It will get slightly warm. If it gets hot or starts bulging, disconnect immediately.

I have to add a disclaimer here: You do the battery testing at your own risk. I have so far had no batteries overheating and only one bulging (it was defective).

Conclusion
This was a really easy and quick project for me. I spent more time designing and modifying the casing than making the schematic and doing the wiring.

The great thing about these modules is that they can be quite complex in design, but are easy to use. Even a beginner can construct otherwise quite difficult projects quite easily.

In conclusion, though there are many ready made modules available of every kind, there will always be some interesting circuits not available in modules, so I still get some enjoyment from designing and wiring my own PCBs.

As mentioned previously, this is my first Instructable. I would like some feedback about where I can make improvements in future.