Single-Cell Li‑ion Solar Charger + 5 V Output (Power Bank Style)

 How to build a Single-Cell Li‑ion Solar Charger + 5 V Output (Power Bank Style)? Charge a protected 18650 and provide a stable 5 V output, even when sun varies.

Chosen specs

• Panel: 20 W, 12 V nominal, Vmp ≈ 18 V, Voc ≈ 22 V, Isc ≈ 1.2 A

• Battery: 1× 18650 (3000 mAh) protected cell (Samsung/Panasonic + protection board)

• Charge current: 1.0 A (gentle ~0.33 C)

• Output: 5 V up to 1.5 A burst / ~1.0 A continuous via synchronous boost

Topology

Panel → blocking diode → buck to 5 V → Li‑ion charger (TP4056+protection) → battery → boost to 5 V → USB.

Panel + ─ Fuse(3A) ─|<|─ +IN  Buck (to 5.0V)  +OUT ── 5V-IN  TP4056(P+)

           SS54           |                         GND ───── TP4056(P−)

Panel − ──────────────────┴───────────────────────────────────────────────

                                   TP4056(BAT+) ── +Batt ── 18650 (protected) ── −Batt ─ TP4056(BAT−)

+Batt/−Batt ──> Boost 5V (synchronous, e.g., MP3429/XL6009 module) ──> USB-A 5V

(Load sharing, simple):

- Feed boost from battery only (most robust). When sun is present, TP4056 charges cell; boost draws from cell.

BoM (example parts)

• Solar Panel: 20 W, 12 V nominal (Vmp ~18 V)

• Blocking Diode: SS54 (5 A, 40 V Schottky) for extra margin

• Buck Module: MP1584EN or LM2596 set to 5.00 V at 1.2–1.5 A capability

• Charger: TP4056 with protection (DW01A + 8205A MOSFET) module

• Rprog (if needed): 1.2 kΩ → ~1.0 A charge; 2.0 kΩ → ~0.58 A

• Cell: 18650 3000 mAh, protected; cell holder

• Boost Module: Synchronous boost capable of ≥1.5 A @ 5 V (e.g., XL6009, MT3608 is OK up to ~0.8–1.0 A)

• Fuses: 3 A panel+, 2 A battery+

• TVS: SMBJ24A at buck input; SMBJ7.0A across TP4056 input (optional)

• Wiring: 18 AWG panel→buck, 20 AWG battery/boost paths

• Enclosure: IP65 box, vents (Li-ion should not be hermetically sealed)

Key settings & safety

• Adjust buck to 5.00 V. TP4056 requires ~4.5–6.0 V input.

• Set Icharge = 1.0 A (Rprog ≈ 1.2 kΩ). If panel is weak/cloudy, use 2.0 kΩ (~0.58 A) for cooler operation.

• Only use protected 18650. Don’t charge <0 °C or >45 °C. Do not parallel bare cells.

• Boost from battery only avoids unstable power-path with TP4056.

Testing

1. Open-circuit: Panel Voc ~22 V. Buck output 5.00 V.

2. Connect TP4056; verify P+ to P− ~5 V, BAT+ to BAT− ≈ 3.7–4.2 V while charging.

3. LED states: CHRG on during charge, STDBY when full.

4. With USB load 0.5–1.0 A, 5 V should remain ≥4.9 V; battery current increases as needed.

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