Introduction: Lithium Battery Utility Board

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UPDATE: there is a new version (1.2). This article explains version 1.0.

I use lithium batteries (mostly in form of the well known 18650 cells) quite a lot. For charging them, I used to use the TP4056 boards with protection, which are available from Ebay for about $0.5/piece. Then I utilized a separate boost converter. But a while ago, I saw a nice video from GreatScott which inspired me integrate this into a single board.

You see his original video here and the associated Instructable here. His work will be referred to as the original design. I reworked the circuit and made the following changes:

  • I included a Load Sharing circuitry. In the original design, it was not possible to charge the battery and output 5 V at the same time (or better it was possible, but it would damage the battery and disrupt the charging).
  • I optimized the layout of the SMPS a little bit, so it is now able to output 1 A without significant voltage drop. The schematics is done to be a little bit more organized and include equations for calculating output voltage, charging current etc. Also, all the source files are available as Eagle files, which at least in my opinion is better than that EasyEDA stuff.
  • I did add a few capacitors, resistors and a "Power Good" diode. Also, all diodes are using such a footprint that you can put SMD 1206 diode over it or solder two wires in there easily, so you can route the diodes to some front panel or similar.

Just for remind you what this board can do:

  • charge a Li-Ion or Li-Pol battery with a current of up to 1 A (the charging includes a precharge, CC and CV stages)
  • protect the battery from overvoltage, undervoltage and short circuit
  • boost the voltage of the battery to 5 V (or any voltage in the range of 4,5 to 28 V)
  • share the load between the battery and the charging input (that means you can charge and use the device at the same time).

All the source files are available in the last step.

Step 1: Performance

Of course, after you build such a circuit you want to know the performance. I have performed a variety of test, of which the most important is probably efficiency versus load current at different battery voltages. Another test is load regulation (that is, how constant is the output voltage at different currents). The last measurement I did was output ripple, which was about 50 mV average and 600 mV peak-to-peak during all tests.

The first two charts are attached to this step as pictures.

Note: because of resistive losses, at 1 A output and 3,0 V battery voltage the actual voltage at the protection circuit was lower than 2,9 V and the protection disabled the output. So you need to raise the battery voltage to about 3,05 or use short thick leads to have 1 A output at 3,0 V of battery voltage.

Step 2: Conclusion

I had the board professionally manufactured in China. After JLCPCB screwed me, I chose ALLPCB and I got the boards in like 8 days, thanks to the free DHL shipping. The quality was very good for the price, so I recommend them.

All of the passive components are 1206 size, so really easy to solder by hand. The smallest IC is the dual N-FET in TSSOP-8 package, but even that can be soldered by hand. Except for the ICs and passives you need just two special components:

  • microUSB connector (or you can directly solder wires to the board, if you want). I used the type with 5 pins and 2 holes, for example available here.
  • 22 μH inductor in 7 x 7 mm package.

The final board is 20 x 50 mm, so you can fit 10 of them on a 100 x 100 mm board. It is also just 2 mm wider than a 18650 cell. In the thickest point it is 6,23 mm.

All the files and photos are also available on my GitHub (and I recommend you download them from there, as there might be some future updates, new features and so).

If you have any questions, comments or suggestions, feel free to leave them below! Also, if you have hard time getting the components or boards manufactured, PM me. I have a bunch of the boards and components lying around, so I might be able to post them to you.

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