Power Node Test Run

I had some time on Sunday and was able work out the issue with the INA169 current sensor (it was a software scaling problem not hardware) on the power node.

I connected the power node to my solar panel for about 9 hours and collected the voltage and current sensor measurements. The area where I placed the panel was not in full sun initially when I began collecting and because of houses and walls this area also becomes shaded later in the day. Below is the plot of the data.
The plot can also be viewed on Plot.ly --> HERE. Viewing on Plot.ly will allow zooming in and analyzing the data in greater detail.

 

Several lessons were learned from this test and will help with the further development of the Distributed Power Node design. Here is a quick outline of the lessons learned:

• The solar panels function very differently from a power supply (e.g. switch mode type). The open circuit voltage of the panels is over 20 volts and under load between 19 and 16 volts. The panels can provide about 4 Amps max. If a 19 volt 4 Amp switch mode PS is connected to the charge controller the PS voltage drops to 4.5 volts. If I current limit the PS with 22 ohms of ballast it will charge via the controller but barely.
• The charge controller appears to provide the peak current of the panel when charging (PWM). I was sampling at a 5 sec rate with the Arduino and in the graph you can see the PV current pulses are in the 3000 mA range, turning on and off to keep the battery changed. Since I can see that current I may be able to calculate the potential maximum power the panel could have delivered.
• There is a need to take multiple sample sets and perform a running average to get a more meaningful PV current reading.
• Because of the way the SCC-3 charge controller works a switch mode PS can not be used for node to node power transfers with it as a source. A separate charge controller for the 300 VDC bus will be needed.
• State of Charge (SoC) and power usage calculation seem to be straight forward in firmware. Calculations made from the graph data agree with the Arduino code power usage. The whole run was about 64 Watt-hours with 28 Watt-hours on battery.

The next test will run for several days with varying loads. The load management code will need to be implemented so the battery will not be over discharged.