For a music festival, I was searching for a way to charge my phone without draining the car’s battery. Since I had an old solar panel laying around, I decided to build a simple solar USB charger. I still had a 16…120V to 12V DC-to-DC converter so I wanted to convert the solar panel’s voltage to 12V first and a car USB charger to charge my devices This way, the system is also more versatile and could be used to power e.g. a little fridge.
Very simple. I just had to connect the solar panel to the input of the 16…120V to 12V DC-to-DC converter and its output to the input of the COTS car outlet. I designed and 3D-printed a small enclosure for the project.
Since two DC-to-DC converters are involved in the charging system (Solar to 12V converter + 12V USB charger), I was a bit worried about the efficiency. Therefore, I decided to conduct a little study:
An USB charger that constantly delivers 5V/2A was connected to the 12V outlet and connected to a power sink. The system was able to provide stable output voltage and current at input voltages of 12V and above. The input current was measured at different input voltages and the efficiency was calculated. The results show an efficiency of approx 80% at all input voltages:
The device was used successfully at the festival. I was able to charge multiple power banks per day and will definitely take it with me next time.