Solar-Powered Power Bank

I wanted an off-grid way to top-up my phone during hikes and discovered I could use a tiny 5 V solar panel. By pairing it with a TP4056 charge controller and an MT3608 boost converter, I got a simple, robust 5 V USB power bank that recharges itself whenever it sees the sun.

How it works:• The solar panel is two strings of 10 cells in series, giving about 5 V open-circuit. Current rises or falls with sunlight intensity.• The TP4056 charge controller accepts 4 – 7 V, charges the Li-Po up to 4.2 V, and shows status: red LED while charging, blue LED when full (or flashing if no battery).• The Li-Po stores energy between roughly 3.4 V (discharged) and 4.2 V (full).• The MT3608 boost converter steps that up to a regulated 5 V for the USB-A output.

Typical performance:– About 150 mA charge current in full, cloud-free sun with good panel alignment.– Roughly 30 – 80 mA under overcast sky.– Behind double-glazed windows the current drops to roughly one-fifth, so place the panel outside whenever possible.

Assembly:

1. Wire the solar panel, TP4056, battery, and MT3608 exactly as shown in the circuit diagram (mind the polarities).

2. Connect the battery via its JST-PH lead.

3. Power the boost converter from the battery and adjust its trimmer until the output reads a steady 5.0 V.

4. Print the enclosure in PET-G (PLA can soften above 60 °C in direct sun).

5. Slide the TP4056 so its LEDs align with the front slot and secure all boards with four 2.2 × 13 mm screws.

6. Fix the solar panel to the frame using strong double-sided tape.

7. Close the lid, expose the panel to light, and verify: red LED = charging, blue LED = full, USB output ≈ 5 V.