The circuit diagram is the equipment setup used to perform the power measurement readings on the Pi4B. The Microchip PoE to USB-C provides replaces the traditional wall wart Pi power supply. To test the power performance of the Microchip PoE, the Pi4B will be subjected to an increasing load thereby demanding more power from the source. The voltage output on pin 1 & 2 (5v & 3V) will be monitored with a volt meter to record any changes.
Two load tests will be used. One is a Raspberry Pi software stress test documented at this link. https://core-electronics.com.au/tutorials/stress-testing-your-raspberry-pi.html . This test is labelled software load. The other test, labelled hardware load, is designed to draw power to light a bank of 28 LED's connected to GPIO outputs.
The software load test runs a series of processes on the Pi which are designed to run the CPU at full power. This test was used in the Raspberry Pi4B (4GB) plus POE Hat - Review . Adding a 28 LED as a hardware load to the Pi4B's output is a simple way to increase the power demand from the source. After completing the hardware load exercise I realized a simple setup would have just been to load up the Pi DC power outputs to draw more current.
The load tests for the Microchip PoE were run using three different cable lengths. 1 meter, 6 meter and 100 meter between the PoE injector and the Microchip PoE to USB-C, labelled cable variable. The longer the length of cable between the two devices the more resistance is added to the power circuit. How does the Microchip PoE USB-C device performance stand-up when the Pi4B is under maximum load on a network cable of maximum length?
An official Raspberry Pi power supply was used initially to get a baseline. It should be noted that the Pi4B shown in the drawing has a keyboard and mouse attached and is also displaying video on a monitor. In addition two miniature cooling fans attached to a heat sink are running from the Pi 5V power supply.
The power test was successful. The results didn't provide any indication of a performance issues using the Microchip PoE USB-C device, even when the load on the Pi was maximum. Executing the code for the software load had the most impact on the 5v power supply output. I was impressed with the Microchip PoE performance, the output of the Pi remained stable when both the software and hardware loads were applied. I was expecting some change in the output voltage when the additional hardware load of 600 mA was added to an already demanding software load. That did not happen.
The change in Pi supply voltage when using an Pi official power supply and the Microchip PoE USB-C is negligible. The change from 5.11v compared to 5.09v is when the load applied demonstrates that.
Continue to read the next blog post, as we proceed to the next round of tests that involve the PiZero. This should be interesting since the Microchip PoE sport a USB-C connector and the PiZero has a USB mini.