Solar Power

Small project to demonstrate solar power, power storage in batteries, and a motor load to spin a propeller.

Parts

• 2x PowerFilm MPT6-150 6.0V 100mA photovoltaic modules - maximum output 200mA
• 1x Low Voltage Schottky 1A diode
• 4x Varta HR6 NiMH 2100mAh 1.2V batteries
• 1x Battery Holder HR6 - four 1.2V equals 4.8V
• 1x Standard 030 form-factor RM1A 4.7V 150mA 7400rpm motor
• 1x Propeller 3.4"

Alternatives:

• 1x Hitec 1600mAH 4.8V NiMH flat battery pack

Setup

The twin solar panel is providing 4.8Volt 200 mA power, the battery 4.7Volt 1600mAh, and the motor a 4.7Volt 150mA load.

NiMH (Nickle-metal hydride) batteries should normally be charged at 1/10C rate, e.g. 1600/10, 160mA. That means it will take little over 10 hours to charge 1600mA. Trickle-charging at this rate will not overcharge and damage the battery (more). NiMH is not like LiPo batteries where the voltage can be used for cut off. With maximum 200mA from the solar modules, it should be charged in 1600/200, 8 hours. That's about the average length of daylight. Also, charging requires a higher voltage, 6V to charge a 4.8V battery.

If the motor is only used at night and free spinning, it should be able to spin 1600/150, 10.5 hours.

A diode will block the current from the battery to flow back to the solar modules when the sunlight is not bright enough to charge the battery.

Stand

To house all the components, I built a stand out of two sheets of plexi-glass and a threaded rod.

Solar modules like to face the sun (for some reason) and a 90-60-30 degree triangle should work fine here. The modules would be fastened to the long hypotenuse sheet between the 30 and 60 degree angles. Pytahoras helped to figure out the different measurements.

Drawing and measurements:

References

• Nickel-metal hydride battery