Tuesday, October 10, 2017

5V Solar Power Supply - testing system

In order to test the solar power supply without connecting the Raspberry (also because used to monitor the solar charger itself), here how I'm proceding.

First of all we need a way to simulate the Raspberry Pi "load" toward the system.
Browsing around the net I found the perfect tool for that, an USB load capable to be set to draw from few mA up to 3A.
I did buy it from Amazon.
Another nice thing to have is an USB voltmeter/current meter like this one :
It is handy to have the voltmeter connected to the load in order to regulate the load to draw the average current used by the Raspberry Pi, around 350 mA.

Then the idea is to use the Raspberry Pi itself, powered externally, to run a monitor program to capture the battery charge/discharge and other conditions, like full sun/night to determine the solar power supply under different conditions.

Block schematic

Here a block schematic about the test environment.

The goal is to have the system set to draw about 300-350 mA from the solar power, simulating the average load of a Raspberry Pi, and see how the system behave in few week run, monitoring the battery charge/discharge via the Raspberry Pi.


As mentioned, the monitoring is done using a Raspberry Pi with the groove system.
At least we need to monitor the battery charge and the amount of light (used to determine if there is sun enough to charge the battery.
The monitoring program, in python, running on the Raspberry Pi is quite simple.
It just open a log file and every 60 seconds reads the value of the voltage and the value of the light.
The data collected in a file  are then displayed on a graph using  gnuplot.