Abstract
This team-based design project resulted in a compact, foldable portable charger that harnesses solar energy to charge mobile devices. The system integrates photovoltaic panels with lithium-ion battery storage and a voltage regulation circuit, packaged in a weather-resistant enclosure. The project combined electrical systems design, thermal management, and mechanical enclosure design, culminating in a functional prototype suitable for outdoor use.
Problem Statement
Outdoor enthusiasts, travelers, and individuals in areas with unreliable grid power often struggle to keep their devices charged. Commercial solar chargers are either bulky, inefficient, or lack adequate battery storage for cloudy conditions. Our goal was to design a device that was portable enough for day trips, effective in varied lighting conditions, and durable enough for outdoor environments.
Design Requirements
- Charge a smartphone from 0% to 50% within 4 hours under direct sunlight
- Store sufficient energy to fully charge a typical smartphone when solar input is unavailable
- Compact form factor: foldable to fit in a standard backpack pocket
- Operate within safe temperature ranges for battery and electronics
- Resist light moisture and dust (IP54 equivalent)
System Architecture
The charger consists of three main subsystems: the photovoltaic array, the battery management system, and the output regulation circuit. Two 6V monocrystalline panels were connected in series to achieve the voltage required for charging a 3.7V Li-ion pack. A charge controller prevented overcharging, and a buck converter provided stable 5V USB output.
Thermal Analysis
A key mechanical challenge was managing heat dissipation. Under full sun, the panels and electronics can generate significant heat. We conducted a simplified thermal analysis using steady-state conduction assumptions to model heat flow from the panels through the enclosure. Ventilation slots were strategically placed to encourage natural convection while maintaining weather resistance. Material selection prioritized plastics with adequate thermal stability (ABS) and UV resistance for outdoor longevity.
Mechanical Design
The enclosure was designed in CAD with a hinged, foldable configuration. When closed, the panels face inward to protect them during transport. The hinges were over-engineered to withstand repeated opening and closing. A rubber gasket provided a moisture seal when closed. The final prototype was fabricated using a combination of laser-cut acrylic and 3D-printed components for complex geometries.
Results & Performance
Testing under controlled conditions showed the charger could deliver approximately 1.5A at 5V under peak sun. Real-world testing during a 3-hour hike demonstrated successful charging from solar input alone. The battery pack provided a full phone charge as a backup. Team roles were distributed across electrical design, thermal analysis, mechanical design, and integration testing.
Key Learnings
- Integrating multiple engineering disciplines (electrical, mechanical, thermal) required clear interface definitions and regular communication
- Prototyping early revealed thermal issues that weren't obvious from paper analysis
- Designing for manufacturability and assembly simplified the final build significantly
Tools Used
SolidWorks, Thermal analysis (hand calculations & spreadsheet), Multisim/LTspice, Laser cutter, 3D printer