Interesting question, no? In preparation for some of my hardware projects, and since I still haven’t received my CM4’s 🤬, I needed some estimation for what the real power draw is likely to be. Yes, there are spec sheets, but they are vague because the actual draw depends on the application.
As you might imagine, I’m not the only one thinking about this. So, you’ll find threads like this one, for example, wanders around the topic a good bit.
So, let’s use my overclocked Pi 4 with NVMe SSD on USB 3.0 and GE Interface for a stand-in. This should represent a reasonable worst case if we stress the CPU and keep the network and disk busy. A Pi 4 also has more components than a CM4 would have and would probably be a useful proxy for the worst case for that reason alone. Why do I care about the worst case? Because that informs what the hardware design has to provide, as much as low current sleep is cute and endearing.
My Sparkfun USB Power Meter is an easy way to get data for a rough order magnitude estimate — it’s super easy to splice into a USB connection.
Here is what I found. While 1.7A at 5VDC is not uncommon under load, and 0.8A to 1A seems typical otherwise, you can find peaks at 2.1A and slightly higher over time. You can see a couple of green pixels just above the 2.1A line in the picture above. So, with some safety margin, if I plan for a 2.5A, I should be ok.
Btw, if you halt a Pi, it still draws 0.352A. Or at least mine does.
Of course, I’ll confirm this measurement when the actual CM4’s get here! Stay tuned..