Because my project is in the field and not in a lab, power consumption is a significant issue.

According to specification an idle Raspberry Pi 3B+ bare board has a current draw of 330mA. The efficiency of the SMP supplying the RPi is 92% giving us 100/92 * 0.33A * 5V = 1.8W and at 12V this requires 0.15A

Lead acid batteries last longer with shallow dis/charge cycles.

Assuming 8 hrs of sunlight per day (winter) discharge at 0.15A amounts to 2.4AH from a 17AH battery or 14% depletion overnight. A float regulated 10W solar charging system will restore full charge in about three hours of direct sunlight.

This closed question is highly relevant. It was closed on the basis that it is an electrical engineering question that does not change if mention of RPi is omitted. I don't agree that the material is off topic because the question behind the question is "What engineering issues do I need to consider to take a Raspberry Pi project into the field?" Many people are not familiar with the terms and concepts they need to ask the right questions and get useful answers.

For example, in my own project the power circuit includes an alternator producing absolutely filthy power, and the starter motor causes a transient voltage drop from 13V to 9V. The starter motor is commutative so there are high current arcs at about 50Hz.

A big capacitor across DC-in takes the strain off the regulator followed by a 100mH choke on the supply rail and another big cap, in a time tested configuration rather appropriately known as a Pi filter. The Pi filter takes care of the transients and the 50Hz hum. This is certainly general EE, but if you want to supply power directly to the 5V rail on the Pi you better know how to condition power or your Pi is not long for this world.

At any rate, to improve operation under cloudy conditions I must get a bigger battery, reduce power consumption or both. There are a number of power saving measures that spring to mind.

  • Slow down the CPU, something I know to be possible under Rasbian.
  • Turn off ethernet, Bluetooth and Wi-Fi
  • Turn off video

I'd like to turn off ethernet after ten minutes rather than immediately so that I can still talk to the unit to update software.

At the moment my software is the default UWP app. I could turn it into a background app and run headless; it doesn't have a UI. Headless would be fine.

Can anyone tell me how to implement any of these items? I was a bit surprised to find that Windows IOT doesn't seem to directly support power management and I hope it's just that I haven't found the documentation yet.

In other questions people report problems arising from wifi being shut down due to idle time, so maybe that one takes care of itself.

In a comment Dmitry tells me his experiments show underclocking is pointless at best and possibly counterproductive. It appears possible to disable devices but I have yet to test this.

  • You seem to have a rather dated idea of power regulators. SMPS have been around since the 1970s, and their price dropped to pennies in the last 10-15 years. You can get a 5V/3A regulator for $2 on e-bay. – Dmitry Grigoryev Jan 17 '19 at 8:54
  • Underclocking the CPU is simply not worth it in my experience. You may be able to save some power by disabling WiFi/BT/video though. – Dmitry Grigoryev Jan 17 '19 at 9:00
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    @DmitryGrigoryev Thanks for the heads up, you are quite right that my knowledge of p/s is 30years old (elec eng at UNI). So I looked up the chip on the $8 adjustable voltage modules I'm using and almost fell off my chair, it is indeed a SMP with an efficiency of ~92%. I knew about SMPs, but I didn't know they got so small and cheap. For $8 assembled I assumed it was a VR. I'm going to have to rework all my power calcs, thanks for waving your magic wand! – Peter Wone Jan 22 '19 at 1:37

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