Solar Powerbank

Solar Powerbank

A power bank is presented in this article that can be loaded via a solar panel.

Required hardware

Circuit

The solar panel consists of twice 10 solar cells. 10 cells each are switched into a row, so that there is a voltage of approx. 5V. A solar cell works practically like a constant current source, the current of which depends on the incurring solar energy. Depending on the internal resistance of the load, the voltage on the module changes U = i * ri. However, the voltage never gets higher than 5.6V.

A charge controller with the chip TP4056 is used to charge the lithium battery. This charge controller has an input voltage range from 4 to 7V and typical 5V is therefore suitable for the solar panel. A load takes place in low light, but the charging current is then low. The voltage on the battery is up to 4.2V depending on the loading status if the battery is fully charged. The charge controller has two LEDs, a red and a blue one. When a load takes place, i.e. charging current flows, the red LED lights up. If the battery is full, the blue LED shines. If there is no battery, but there is voltage from the solar cell, the blue LED and the red flicker also lights up.

In order for the 5V to be located at the output of the 5V circuit, a step-up converter is required, which places the voltage of the battery from 3.4 to 4.2V to 5V. The entire circuit thus looks like this:

Another note on the performance. With a cloudless sky, a charging current of approx. 150 mA is reached with optimal alignment. With a covered sky 30 to 80 mA.

Danger!

Behind a window pane made of insulating glass, the charging current goes back to a fifth.

Assembly:

First, the individual modules are connected and soldered using the switch wire according to the circuit. Always pay attention to the correct pole. Now infect the battery and set the output voltage to 5V with the potentiometer on the step-up converter.

The two housing parts are made on a 3D printer. One should keep in mind that the power bank will be exposed to the sun for a long time and therefore gets quite warm. PLA is not so well suited because this material becomes soft from approx. 50 to 60 ° C and can deform. PETG is more suitable. The picture shows how the individual modules are accommodated in the housing. Due to the slot at the charge controller you can see the status LEDs from the outside. The solar module is glued into the frame with double -sided adhesive tape.

Of the Blog post by Miguel Torres Gordo to the Solar Tracker Could also be interested in optimizing the yield of the sun's rays.

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