DV8P USB
This page describes the Solar Charger.
Summary
The goals of this project were to improve on existing chargers by increasing the solar panel area and thus charging rate, increasing the available output current for charging other devices, and displaying more useful information to the user. A device similar to the WN805 was purchased and reverse engineered. The device in question did not have sufficient charge rate to justify the solar panel (~0.5W in direct sunlight), and was designed to light an LED and display the current state of charge (via 4 LEDs) when under sufficient light. The threshold was set low enough such that near the threshold (e.g. indoor lighting), the device would self-discharge significantly faster than the solar panel could charge. The maximum output current at the USB port was also limited to ~500mA based on the boost converter design. There were also concerns of back-feeding or destroying devices due to the selectable output voltage and single USB port for both charging/discharging. The Solar Charger described below was designed to improve on all of these areas.
The features of the Solar Charger are as follows:
- Backlit 128*64 Graphic LCD for displaying state of charge, charge and discharge rate
- 5.5V output at 1-1.5A (5.5-8.3W), automatically limited/switched based on battery voltage
- ~80% efficiency boost converter
- Solar charging rate of ~500mA (~1.8W) in direct sunlight, ~30mA (~100mW) in indirect daylight
- 4.4AH low-profile LiPo battery with internal fuel-gauge and protection circuitry
- 13.8mm profile at maximum height (USB connector), 7.2mm profile elsewhere
- Single-button interface to turn on/off USB output
- Recharge at 0.5-1.2A (automatically switched via dedicated charging port detection) from standard micro-USB port
Testing
- 78% efficiency at 3.708V/3.405A (5.57V/1.765A out)
- 85% efficiency at 3.955V/3.038A (5.57V/1.836A out)
Revisions
- 1.0: Initial revision.
Bill of Materials (v1.0c)
| Part | Quantity | Unit Cost | Total Cost | Source |
| USB Micro B to USB Micro A OTG Cable | 1 | $4.15 | $4.15 | eBay |
| USB Micro B Receptacle | 1 | $0.46 | $0.46 | Digi-Key |
| USB A Receptacle | 1 | $0.63 | $0.63 | Digi-Key |
| AP2401 | 1 | $0.50 | $0.50 | Digi-Key |
| 2N7002P | 2 | $0.14 | $0.28 | Digi-Key |
| 0603 Capacitor | 3 | $0.0096 | $0.03 | eBay - mib_instruments |
| 0603 Resistor | 2 | $0.00294 | $0.01 | eBay - mib_instruments |
| PCB | 0.7"x1.35"/3 | $5.00 | $1.57 | OSH Park |
| Total Unit Cost | $7.63 |
Bill of Materials (v1.0)
| Part | Quantity | Unit Cost | Total Cost | Source |
| USB Micro B Extension Cable | 1 | $1.44 | $1.44 | eBay |
| USB Micro B Receptacle | 1 | $0.46 | $0.46 | Digi-Key |
| USB A Receptacle | 1 | $0.63 | $0.63 | Digi-Key |
| AP2401 | 1 | $0.50 | $0.50 | Digi-Key |
| 2N7002P | 2 | $0.14 | $0.28 | Digi-Key |
| 0603 Capacitor | 3 | $0.0096 | $0.03 | eBay - mib_instruments |
| 0603 Resistor | 2 | $0.00294 | $0.01 | eBay - mib_instruments |
| PCB | 0.7"x1.35"/3 | $5.00 | $1.57 | OSH Park |
| Total Unit Cost | $4.92 |
PCB/Construction Photos
- Rev0VTx VCO PCB Bottom.jpg
Bottom of unpopulated PCB
- Rev0VTx VCO PCB Top.jpg
Top of unpopulated PCB
- Rev0VTx VCO Top.jpg
Populated PCB