Test power consumption/CPU stability with stress and Kill-a-Watt

geerlingguy / raspberry-pi-dramble

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Test power consumption/CPU stability with stress and Kill-a-Watt #14

Closed geerlingguy closed 9 years ago

geerlingguy commented 9 years ago

This will be helpful information when it comes time to work on a potential inline UPS.

Some numbers:

Pi State	Power Consumption	Per Pi (average)
Idle	170 mA (7.2W)	28 mA (1.2W)
400% CPU load	230 mA (11.4W)	38 mA (1.9W)
400% CPU load, 1x USB 64GB SSD	300 mA (13.6W)	50 mA (2.3W)

These readings were taken with the Pis in the following configuration:

6x Raspberry Pi 2, all powered on.
Headless (no video displays attached).
No USB devices attached (except as noted).
Onboard LAN connected to Gigabit network switch.
Powered via 6-port USB power supply.
Kill A Watt meter (for measurements) was plugged into wall, then USB power supply was plugged into the Kill A Watt.
CPU stress tests were done using stress -c 4 to max out all 4 CPU cores.

geerlingguy commented 9 years ago

I'll be monitoring the power consumption over a few days' worth of testing, but this is much better than I originally hoped. Running Pis headless seems to save a TON of energy. Most other benchmarks must be run with a display attached, a keyboard and mouse, and maybe a WiFi dongle.

geerlingguy commented 9 years ago

So this is extremely odd...

I was using a Kill A Watt for the original tests (and still had it running today when doing new tests), and I bought a Mini USB Charger Doctor to do inline load tests so I could see how the power is distributed to each Pi.

Today's measurement of one of the Pi 2s:

Pi State	Power Consumption
Idle	420 mA (2.1W)
`ab -n 100 -c 10` (uncached)	900-1200 mA (~4.5W)
400% CPU load	800-1100 mA (~4W)

Interesting...

geerlingguy commented 9 years ago

Measurements on the database Pi:

Pi State	Power Consumption
Powering on, 1x USB 64GB SSD	900-1400 mA (~4.5W)
Idle, 1x USB 64GB SSD	960 mA (~4.8W)
`ab -n 100 -c 10` (uncached), 1x USB 64GB SSD	1100 mA (~5.5W)
400% CPU load, 1x USB 64GB SSD	1250 mA (~6.25W)

geerlingguy commented 9 years ago

Continuing further research on the wiki: https://github.com/geerlingguy/raspberry-pi-dramble/wiki/Power-Consumption

geerlingguy commented 9 years ago

Also of note: apparently the Kill A Watt is pretty inaccurate at lower wattages/amperages... see:

Apparently it does a lot better in its sweet spot, likely 50-1200W or so. The USB current doctor, or a decent multimeter, is probably the best option here... though not as simple as the Kill A Watt.