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by tzs 144 days ago
> I think the Pi 3 range is a sweet spot for low cost, low power draw, decent-enough CPU. Newer models draw increasingly more power; going from 1.4W to 2.8W may not seem like much, but that's half your battery life.

Is that with the same load? The chart in the article shows a Pi 3 and Pi 4 using the same idle power, with the 4 drawing more under full load. But the 4 can do more at full load, raising the question of what would be the 4's power usage running a load equal to the 3's full load?
2 comments
0xbadcafebee 144 days ago
The author's chart is incorrect. He has the idle power at "1" for the Pi 2, "2" for the Pi 1/3/4, and "3" for the Pi 5. No other published power draw numbers are whole numbers like this, they are floating points, like 1.2, 1.9, etc. Google around and you'll find several different power testing comparisons with more detail.

Most reports show the Pi 4 drawing ~2.8 W in idle headless mode, and the Pi 3B+ drawing ~1.9-2.0 W in idle headless mode. With full load the Pi 4 draws more (6.4W, to the Pi 3B+'s 5.1W) with the same test procedure.

But you do have to check the testing method; enabling/disabling hardware features changes the figure, and each additional USB peripheral draws more power. Otoh, to get a "max power draw" reading you have to enable everything and stress all CPUs at once, and then it will dip under thermal load.

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tzs 144 days ago
I had Home Assistant on an RPi 3 with 1 GB RAM and a USB thumb drive until sometime maybe 7-10 days ago when I switched to an RPi 5 with 8 GB RAM and the 256 GB SSD and NVME had sold by the RPi company.

The 3 was and the 5 is plugged into an energy monitoring smart outlet. Here's a graph of power for that outlet [1] for the last 30 days.

HA uses long term statistics for older than 10 days, which is why the 2/3 to the left shows much less variation. The switch from the 3 to the 5 is somewhere a little way into the right 1/3, where it is using shorter term data which has a much higher sample rate.

It does look like the average power goes up with the 5, but not nearly as much as I would have thought. The left 2/3 which was definitely all RPi 3, averages 2.48 W. From Jan 17 to the present, which was definitely all RPi 5, it averages 2.64 W.

If those reports of 2.8 W for an idle 4 are accurate I'm curious why my HA 5 is lower. I've got an unused energy monitoring smart plug of the same kind my HA Pi is on. I'll have to put the 4 on that and see how it compares.

[1] https://imgur.com/a/qa7SD2O

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MBCook 144 days ago
Right. In CPU scheduling this is the “race to idle” idea.

Sometimes it’s more efficient to run a task at full CPU power for 25ms than low (non-idle) CPU power 100ms.

It wouldn’t surprise me too much if the 4 could run the 3’s full load in less power than the 3 does.

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