Introduction: Portable Power Supply Unit

The inspiration for this project came from wanting a method to recharge my drone batteries out in the field. Another good time of use would be for camping. This build isn't necessarily the cheapest alternative. There are many commercially available products out there that offer a lot for a reasonable price. I had about half of the components needed just sitting around. Plus I wanted something to do in the past time, so I decided to build rather than buy. If you have none of the items under the materials and cost section, expect to spend 400+ U.S. dollars for the total. That amount can buy a decent setup already finished. Otherwise if money and time is something your looking to use up in return for a working portable power supply of your own along with the experience, then this build is perfect.

The Specifications of my build:

  • 4S (Series) 20P (Parallel) 16.8V Battery Bank (93.6 Watt Hours)
  • 4S 40Amp BMS
  • 300 Watt Inverter
  • 6 USB Charging Ports
  • 1 120V US Outlet
  • 100 Watt Solar Panel
  • 11 Amp Charge Controller

This device can meet your own specifications according to how you want to build it and what you want it to include. If your wanting larger capacity battery, or more outlets, a greater power output (larger inverter), and so on than you should account for the dimension of those objects prior to buying the case. The case I used I chose becasue of price point, availability, as well as the water proofing seal. If you intend to replicate everything exactly than just purchase what is listed below.

I have no affiliation with the websites that are linked, only a consumer of them. I tend to shop around on the internet for a while prior to making purchases and found that these are the greatest value for the smallest dollar amount at the time that I purchased them comparing to what else was available. To get the absolute lowest prices for most items I would recommend buying directly from China. Only downside is expect the delivery to arrive in one to two months on average. I have made hundreds of orders from this year alone and received exactly what I expected sometimes within three weeks

Materials And Cost

Batteries (80) 18650 Cells

Nickel Strips .1, .12, OR .15 thickness


14 Gauge Silicone Wire

26 Gauge Silicon Wire Need to have two different colors

(2) Rocker Switches Only need one switch if you want to install a temperature sensor/controller to automatically control the fans.

Digital Temperature Controller

XT60 Connectors (Not Soldered) OR XT60 Connectors (Already Soldered)

Fans (2) 12V DC

Battery Indicator

Digital Meter

Six Port USB Charger

Step Down Buck Converter

Case If you go with another case these designs won't fit in it. Pelican has files you can download for CAD software to incorporate your own face plate designs.

Silicone Sealant

Solar Panel, Charge Controller, And Inverter

1 KG of PETG or ABS Filament

M1-M5 Screw Assortment

Shrink Tubing

VHB Tape

300mm Shrink Tubing

(16) 10 X 3 mm Magnets

Super Glue

Total Cost $550+/- including solar panel, which most commercial products sell separately, and depending on what battery capacity you buy can be lowered significantly. Also depends on supply and demand so prices may change.

Tools Needed

3D Printer
Soldering Iron


Heat Gun Or Small Torch

Battery Spot Welder

Wire Strippers

Wire Crimper Tool With Terminal Sleeves

Small Flathead

2.5mm, 3mm, 4mm Hex Keys

Wowstick isn't required but it handy to have if you do a lot of projects with small screws.

C4 18650 Battery Charger

Digital Multimeter


Drill Bit Set

Step 1: Battery Bank

This step is really a whole other project in of itself.I bought used batteries that had previous spot welding scars so I used a rotary tool and small cutoff wheel to grind those off. After both ends are cleaned on all cells, it is recommended to charge them using a smart charger like the C4 listed in tools section.

For good tutorials on how to assemble your own battery banks as well as how to connect up BMS's than I recommend Jehu Garcia and Ebike School Channels. If you have done battery bank assembly, experienced with spot welding batteries, and wiring BMS's then you can probably skip to Printing and Assembly.

Once all cells are charged up, test the voltage of each cell. Anything below 3.6 volts should be disposed of. On average I had cells around 4 volts each. Multi-meter's vary greatly on how they appear. Perhaps consult the manual to find the exact icon, symbol, or letter for DC voltage testing. On my meter to check the voltage I switched the digital multi meter to a DC 6V setting and apply the black to the negative and red to the positive.

To arrange the cells, place the batteries into one of the printed 18650 4S 10P Plate. One row all the way though should have the same end facing upward (positive or negative). The next row over should have the opposing end facing upward (positive or negative). Refer to pictures included.

After all the cells are arranged and press into the bottom plate. Set the other plate on top of the batteries. If it seems like a tight fit, start at one end and lightly hammer it onto the batteries one or two cells at a time and gradually move over towards the other end of the battery bank. The two plates should be holding them all in place with no flex.


Be very careful and take your time with this next step, it can shock you and possibly short out the batteries. Clear out any nearby conductive material so you don't accidentally set the battery on top of it making an electrical connection.

If you are satisfied with your brick of batteries, then it is time for spot welding. If you use same spot welder as I did, you will have to get .1-.15 thickness, this welder cannot weld thicker than that. The placement of the nickel strips matters. Easiest way to explain is to refer to the pictures I have included for the exact layout. Cut and place the nickel strips onto the battery. Hold your battery up to the welder with a fair amount of pressure and tack it once, check it out, and tack it once more and move on to the next cell.

Eventually you will have finished spot welding. Now time for wiring up the battery management system (BMS). A BMS monitors and distributes the current evenly across all connected cells. The thicker (14-18 gauge) wire that is red and black was so I could turn 10P to a 20P battery bank. Normally this would be done by spot welding more strips in the same pattern, but to fit in this specific case I needed the two bricks to be side by side rather than one long rectangle.

Mount (hot glue) the BMS to a insulator type material like a hard plastic, foam, or cardboard. Do not mount it directly to the side of the batteries.

The other thinner (28-30 gauge) wires are all connected to various points on the BMS. I used the same color codes for the same point on the BMS. Black is 0V, Yellow is 4.2V, Green is 8.4V, Red is 12.6V, and Pinkish is 16.8V. Each number has two wires becasue it needs to be connected to the first cells and the last cells in parallel. If you did one long rectangular battery bank your wires would start at on end of the bank and the second wires would stretch to the other side end of the block. I used a soldering iron to the nickel strips as to not damage the cell.

Finishing up the battery is easy. Solder on one red and one black thick (14 gauge) wire about 6 inches in length at the least, with a XT60 connector on the end. This goes onto the + and - symbols on the BMS. I applied some kapton tape to halp keep the block from shifting around. Slide the battery bank into some 300mm shrink wrap, cut away the excess, and apply heat gun or torch with some distance. Battery bank is now complete.

Step 2: Printing and Assembly

If your completely new to 3D printing I suggest you read below otherwise you can skip to print settings section.

I have two Ender 3's. Both of which are really good quality for price point and can handle PLA, ABS, and PETG. Bed adhesion use to be the biggest problem despite mastering bed leveling. The thing that eliminated that issue for me was throwing out the stock beds and replacing with tempered glass. Of course had to level it again but only once. Before each print I wipe it down with some 70% isopropyl alcohol. Let your printer preheat fully. Keep the printer and filament in a dry area. More humidity means more problems. The beads likely won't laminate properly causing easy separation between two layers in the middle of a finished part.

If you don't have a 3D printer yet and are considering obtaining an Ender 3, follow this build tutorial closely. I followed all the steps on both printers I assembled and came out perfect on the first attempt. I user Cura for the slicer. Many setting options included plus it's free to use.

Print Settings

This link is for the STL files

ABS or PETG recommended. The greater the infill percentage the better. I chose 25% for all four face plates. I used 0.8 nozzle at draft quality and had a decent looking product in an average of five hours per part. These need supports and to be oriented with letters facing to the sky.

The interior components were printed using 0.6 nozzle at standard quality.

(1) Flat Bracket 100% infill

(4) Bowties 100% infill

(2) Magnet Bars 75% - 100%

(1) Charge Controller Bracket 75% - 100%

(1) Buck Convertor Mounting Bracket 50% infill. There are two versions. You only need two bolts to mount it to case so I designed a 2 hole as well as the 4 hole. But only need to print one or the other.

18650 Battery 4S 10P Plates 100% infill with 0.4 Nozzle at standard quality. I did this with PLA as it will be wrapped and then enclosed again in a case. Depending on how many batteries you intend to use (40 cells = 2 total 4S 10P Plates needed) (80 cells = 4 total 4S 10P Plates needed)

Assembling these together is basically like lego blocks. The bow ties are to help hold plates together, but not needed. What secures everything together the best is the magnet bars as well as the pressure of the tight fit from the case When inserting magnets into the parts, I had a stack in hand, applied some super glue into the part, and pressed in one magnet with the stack on top of it. This was so the polarity is reverse and the magnets are accidentally glued in the wrong way.

Once a magnet bar had four magnets glued in an pressed all the way in I let it dry for some hours. I gave each of the four magnets a second magnet to stay connected to it. This way the polarity is already correct for when the face plates are glued and press onto those magnets.

Step 3: Mounting and Wiring

Refer to the included flow charts for how I wired things up.

Wiring everything together is not very complicated, that is just how it appears. For most components, they involve only positive and negative wires. The switches is where it gets a little bit tricky. If you intend to have automated fan control using a digital temperature controller/sensor, then all you need is one rocker switch to power the device on and off. If you want other utilities such as a LED light bar or something, in that case you would likely want to utilize a second switch.

Before you solder anything together remember to place the meters and switches into the printed face plates first. Or else you will have to do it twice. I learned this the hard way. When mounting the fans ideally you want air circulation to one should pull air in and the other blowing air out. The inverter also has a fan which blows the air out the back of it.

For the inverter I dis-assembled it down to just the circuit board temporarily. You do not need to do that much but to extend the reach of the 120V outlet you will have to perform some dis-assembly. Do not do this while plugged into anything. Four screws on bottom plate expose everything. Four more screws on the front plate (with the outlets) need to be undone. Push out the outlet plugs from the front plate. The plate was not removable unless the wires were cut or the front plate was cut.You can probably just cut the wires cause the next step involves cutting them anyway to extend the reach.

I chose different route and cut away small notches into the from plate carefully using a rotary tool. Then took pliers and bent them so I could slip the outlet sockets through. Then I realized I need to splice and solder in about six inches or so of wire. Only has a total of three wires to extend. I suggest they be cut, spliced, soldered, and shrink tubed one wire at a time. This allows for the extension of the outlet socket to reach the face plate for the case. After that modification has been made, you will need to put the bottom panel back on the inverter and prepare mounting brackets.

I used aluminum extrusion angle bar. Marked position for holes, drilled holes, and sawed the piece off of the bar stock. I have designed the brackets so they can be 3D printed to make your life a little easier. Refer to the pictures to see how I mounted them to the case. Before you drill any holes make sure you are satisfied with your layout and that the battery doesn't slide around too much. I pushed my battery bank up tot the right hand corner of the case, inverter right up next to that, and then drilled the holes. When you drill your holes the buck converter mounting bracket should be mounted first becasue there isn't enough clearance to drill holes for it with inverter mounted in the way.

I only drill holes through the case for these two brackets and two holes for the mounting bracket designated for the DC-DC buck converter. Before I placed a screw/bolt through said hole I would apply silicone sealant on interior and exterior to keep it water proof. I also used washers on both ends of the bolts. I designed the magnet bars to have the ability to be secured to the case by bolts as well.

On my PPSU, I used VHB tape to stick the charge controller onto the side of the case. While creating this instructable I took the time to create a bracket you can 3D print and drill holes to bolt up if you wish. The only other area I used a small amout of VHB tape was between the flat bracket and the solar plug to keep from sliding when plugging into solar panel connector.

I hope this has been inspirational, informative, or somewhat fun for you. Thanks for viewing my project.