This was a project that resulted from another. (Check out The Ultimate CNC Bluetooth Speaker


After creating my Bluetooth speaker, I found myself in need of a charger. I had been charging it off a variable DC power supply, but wanted something more permanent. So, I wired up a circuit to output 12.6v, the input charging voltage for 3s lithium batteries. While I was at it, I decided to add a USB charger to it as well.

In this Instructable, I will detail my charger, along with two more simplified circuits for the everyday DIYer. Overall project cost could be between $10-$25, depending on which circuit you choose, how many cells you wish to put in it, and what you can scavenge.


Charger with 12.6v output and 2 USB ports (Duplicate of mine)

· 2x 18650 lithium cells https://www.amazon.com/EBL-3000mAh-Li-ion-Recharg...

· 1x Dual USB output charger circuit (input voltage 5-12v) https://www.amazon.com/Output-Charger-Switch-Supp...

· 1x DC-DC step up converter (Pack of 2 is same price as one) https://www.amazon.com/Gowoops-Converter-Voltage-...

· 1x Micro-USB 3.7v charger board (Pack of 5 is same price as one)https://www.amazon.com/McIgIcM-Lithium-Charging-Pr...

· Wire

· Printer Filament

· Wood (Mahogany in my case)

Charger with 2 USB ports

· 2x 18650 lithium cells https://www.amazon.com/EBL-3000mAh-Li-ion-Recharg...

· 1x Dual USB Charger https://www.amazon.com/Output-Charger-Switch-Supp...

· 1x DC-DC step up converter (Pack of 2 is same price as one) https://www.amazon.com/Gowoops-Converter-Voltage-...

· 1x Micro-USB 3.7v charger board (Pack of 5 is same price as one) https://www.amazon.com/McIgIcM-Lithium-Charging-P...

Charger With 1 USB Port

· 1x 18650 cell (2 pack is the same price as one) https://www.amazon.com/EBL-3000mAh-Li-ion-Recharg...

· 1x DC-DC step up converter (Pack of 2 is same price as one) https://www.amazon.com/Gowoops-Converter-Voltage-...

· 1x Female USB port (Here is a pack of 10, no single piece order available through Amazon) https://www.amazon.com/uxcell-Office-Straight-Sol...

· 1x Micro USB 3.7v charger board (Pack of 5 is same price as one) https://www.amazon.com/McIgIcM-Lithium-Charging-P...

I realize that you may be ordering extra boards, but many of these come in handy in other projects.

*Note: There are cheaper options for many of these, I have just selected parts that looked trustworthy to me. Use these as a guideline if you must.

Step 1: Explanation of Parts

If you have had any experience with these boards, go on and skip this explanation. This is geared toward those with little understanding of circuits.

Lithium Cells

These are 18650 cells. They look like oversize AA batteries. Many believe that it is absolutely necessary to have an external over-discharge circuit attached, but I do not believe it to be necessary. If the batteries go to too low of a voltage, they will not be able to charge anything anyway. Your device will not register as charging. That's how to tell when to charge your portable charger.

Dual USB Charger Board

These boards accept an input voltage from 6-12v. That is why we must use a step up converter for them, because lithium cells' maximum voltage is 4.2v. They convert that voltage range to 5v, and regulate it for you.

DC-DC Converter

As you may know, transformers are how to adjust voltage in AC circuits. These little circuits switch DC on and off rapidly to produce an AC-type effect, and depending on how you adjust the screw, gives you a higher voltage.

Micro USB 3.7v charger board

These things are tiny. You plug in your micro USB (5v is standard for all USB devices), and it spits out 3.7v - 4.2v to charge your lithium cells. This will charge your charger.

Wiring these together will come later.

Step 2: Wiring for Dual USB Output

First off, I will point out that I did not use 18650 cells for my charger. I happened to have a lithium pack lying around. 18650 cells are recommended, however.

I have attached a visual schematic of my circuit setup. It is fairly simple. First, you connect the leads on the cells you're using. (Connect both the positives together, and both the negatives together.) Do not short-circuit the batteries. Then, you will need to connect a pair of wires to each positive and negative lead. One set connects to the output of the 3.7v micro USB board. The other connects to the input side of the DC-DC converter. Polarity does matter with these, so don't get them mixed up.

Before connecting the USB converter to the output, you'll need to check that the output of the DC-DC converter is between 6-13v. I put mine to 12.6v, so I could wire in a DC output jack to charge my speaker. Apply the leads of a multimeter to the output, and measure the voltage. You can adjust the output by turning the small screw on the converter. Once you get it where you want it, leave it be. Now you can connect the output of the converter to the USB board.

Now, test your circuit. When you plug in a micro USB, the board should light up with a blue or red LED, depending on whether your batteries are charged or not. Also, plug something into the USB ports, and make sure they both work. Testing this part with an Apple device would be wise, because Apple devices are much more picky about what chargers will work with them.

Step 3: Wiring for Single USB Output

This circuit requires one less board.

Wire up your cell so that it has a positive and negative lead. Once again, these will connect to both the 3.7v board, and the DC-DC converter. This time, however, adjust the converter so that it outputs 5v.

Now for a simple hack. (This is also explained in my other Instructable).

All you need is your 5v converter, and a couple of resistors. You create a miniature and basic voltage divider. I just found two resistors where one was approximately 2/3 the resistance as the other one. I used 390 ohm and 470 ohm resistors, but any similar proportion of resistances should work. Connect them in series, and have the two data lines (the green and white wires) connected at the junction of the two resistors. The positive and negative wires (red and black) should be connected separately to the other ends of the resistors, with the larger value resistor containing the positive lead. At the end, put some heat shrink or electrical tape on the whole bundle. Refer to the pictures, it should help. What this does is steps down the voltage to about 2.25v. By experimentation, with this voltage I have found that it tells your iDevice to pull up to 1A of current. This should be a healthy amount for most devices you charge by USB. Don't worry about what wattage your resistors are rated for, as the voltage they push out is only "seen" by the iDevice and not actually used for charging. The 1A of power comes through the positive and ground wires of the USB.

Step 4: Casing

If you plan on carrying this around, you're gonna need a durable case. I used a 3D printer and a CNC to make mine. I realize most people don't have access to these things, but I'll include my files anyway. Optionally, you can print everything. The .tap files are for a 3-Axis CNC, and units are in inches.

If you don't have access to a printer, that's okay. Many different things work for cases. I chose to make mine with machines because it makes the mounting holes exact.

Make sure that you mount everything securely in your case, because if you seal it up, only to drop it and break a wire in there somewhere, it's a lot of work to fix it.

Step 5: Final Thoughts

I have found these methods to work well. If you have concerns about the circuit, please ask me in the comments.

I have found that this will charge my speaker for about 2-2.5 hours, or charge my phone a couple of times. It is pretty durable, and looks nice.

Some quirks:

  • The heatsink on the DC-DC converter gets fairly warm. Do not be surprised if you feel a warm spot on your charger.
  • My CNC files were a little off. The wood is a bit more hefty than I would have liked. But, I don't think it will ever break
That's it! Thanks for checking out this Instructable, and be sure to check out my other on the CNC Bluetooth speaker. Few people would be able to make all of it, but there are parts (especially with the internal circuit) that most anyone could do.
-Peter, Basement Engineer
<p>Linear regulators are bad when you have battery, try to use buck converters as they are more efficient, also less heat</p>

About This Instructable




Bio: I'm a high school student with a passion for engineering, high voltage, and cool projects in general. I have made a 5ft Tesla Coil ... More »
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