Sojourner/Spring/2019
Solar Panel Implementation and Testing
Authors: Connor Hearn and Cole Bailey
Table of Contents
Introduction
The Sojourner can fit three 80x55mm solar cells on top of it. The solar panels are connected to a micro USB cable that is plugged into the 3Dot board to charge the battery that powers the Sojourner.
Solar Panel Implementation
The solar panels will be connected together in parallel to boost the current of the system as needed. The wires from the solar panels will be connected to a micro USB cable that will be fed through the solar panel and cell phone tray. Inside a USB cable there are wires for power and ground which can be soldered to the solar panel wires. A diode will be connected to the red wires to prevent current from going back into the solar panels.
Figure 1. A block diagram implementation of the solar panels.
Figure 2. The inside of a micro USB cable showing the power and ground wires.
Solar Panel Tests
The solar cells were connected in parallel. The voltage and current were measured when they were connected to the 3Dot board when the battery was full and when it was drained. Additionally, the voltage and current was measured when the solar panels were connected to varying resistors. In each situation, the voltage and current was tested when the solar panels were pointed directly at the sun and facing 90 degrees away from the sun. Each case was performed around noon with clear skies.
| Voltage (Directly at the sun) | Current (Directly at the sun) | Voltage (90 degrees away from the sun) | Current (90 degrees away from the sun) | |
| Fully charged 3Dot | 6.15 V | 9.4 mA | 6.05 V | 8.3 mA |
| Drained 3Dot | 5.5 V | 110 mA | 5.25 V | 73 mA |
| 10 Ohm Resistor | 2.6 V | 303 mA | 186 mA | |
| 1k Ohm Resistor | 6.2 V | 5.6 mA | 5.6 mA |
Conclusion
The Sojourner’s 3Dot board can be charged through its micro USB port. It can fit three 80x55mm solar cells on top. These solar cells were connected in parallel to apply enough current as needed, seen from the difference in current between when the 3Dot’s battery was full or drained. The diode in the system prevents the current from going back into the solar panels.