sebasboy
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raspberry pi 3b+ lowering power consumption to absolute minimum

Sun Sep 19, 2021 4:18 pm

hello good day.

im working on a project that in the basics wil make the pi a router.

what wil happen is

the pi connects to a wifi network as client.

then bridges the connection to ethernet where it wil connect its client to wifi.

thats all the system wil do. i got openwrt on the pi and the setup in test mode.

so far i have disabled the HDMI circuity and the power consumption at idle is 0.49 amp at 5 volts so thats 2.45 watts.

my goal is for the pi to not exceed 1.8 watts under its max load. (preferred is 1.5 watts since that means it beats my current setup)

the system wil not even reach gigabit speeds (i think the max the troughput of this system wil be is about 100mbs at best)

i read that disabling gigabit also helps alot in power consumption.

anyway.

my goal is to disable 2 or 3 cores for the pi. underclock the cores. and thus allow me to undervolt the cpu so it consumes less power.

the pi is powered off the clients motherboard (going to tap the voltage from the pcb)


my question is what are my options?

i already looked in the documentation for the boot config but the information about the undervolting is a bit unclear for me and i'd like to have it latest cleared up before i start touching the voltage

renice123
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Tue Sep 21, 2021 1:35 pm

In addition to the well-known ways to reduce power consumption (like giving up crazy "default services" and turning off hdmi output), I think the most effective solution is to use Rpi 3A +
This RPi version clearly outperforms the "regular" third version in terms of power consumption, provided you plug in an external Ethernet adapter (or use usb). I think you can also slightly lower the supply voltage to the permissible limit (for example, to 4.7 V), which will also save electricity. But Zero can be made to work even more efficiently! viewtopic.php?f=28&t=276070&p=1826413#p1826413

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davidcoton
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Tue Sep 21, 2021 2:12 pm

renice123 wrote:
Tue Sep 21, 2021 1:35 pm
... I think you can also slightly lower the supply voltage to the permissible limit (for example, to 4.7 V), which will also save electricity.
Only, possibly, in the attached USB peripherals (which specify a minimum voltage of 4V75 at the Pi). The regulators (for 3V3 and below) on the Pi are switched mode, so reducing the voltage will increase the current, for no net saving in power. It may also make the regulators run less efficiently, resulting in increased power consumption.
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cleverca22
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Thu Sep 23, 2021 2:20 am

just as another data-point, i have a pi2 idling at 0.32A currently, which comes to around 1.6 watts

if you dont need the cpu power, you could maybe switch to an older model?

renice123
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Fri Sep 24, 2021 5:48 am

Well, if we are talking about a real reduction in power consumption, then you will also have to choose a memory card. Different memory cards consume current in different ways, as well as in read or write modes. You can reduce power consumption by giving up frequent recording to the memory card and choosing an energy efficient sd
Also, "in theory" you can reduce power consumption if you solder the wi-fi antenna. I think the power of the wi-fi transceiver-transmitter is automatically adjusted, although in theory some adapters allow you to manually adjust. That is why it is preferable to use an external wi-fi adapter with the ability to regulate power consumption.

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davidcoton
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Fri Sep 24, 2021 8:25 am

renice123 wrote:
Fri Sep 24, 2021 5:48 am
Also, "in theory" you can reduce power consumption if you solder the wi-fi antenna. I think the power of the wi-fi transceiver-transmitter is automatically adjusted, although in theory some adapters allow you to manually adjust. That is why it is preferable to use an external wi-fi adapter with the ability to regulate power consumption.
Not true, and potentially illegal.

The Pi is certified with the on-board antenna. Attempting to connect an external antenna will invalidate its type approval.

You would also need to know enough about RF propagation to make sure a new antenna is actually more efficient than the on-board one. Though I will concede that the on-board is at the low end of efficiency. If that is the cause of excessive power consumption, you need a Pi without WiFi and an external USB WiFi adapter.

Setting WiFi power is not dependent on using an (illegal) external antenna.
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renice123
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Sun Sep 26, 2021 1:24 pm

However, returning to lower power consumption. Today I took a look at how well the processor tuning utilities work. Wow! Great result!
cat /sys/devices/system/cpu/cpu0/cpufreq/ scaling_available_governors
Therefore, we can change the processor operating modes from "efficient" to "energy saving" This is done from sudo
for i in 0 1 2 3; do cpufreq-set -c $i -g ondemand; done
for i in 0 1 2 3; do cpufreq-set -c $i -g powersave; done
cpufreq-info

It might make sense to set up disk writing manually.
Dirty ratio
echo 20 > /proc/sys/vm/dirty_ratio # "normal mode"
echo 90 > /proc/sys/vm/dirty_ratio # for energy saving

Dirty background ratio
echo 10 > /proc/sys/vm/dirty_background_ratio # "normal mode"
echo 1 > /proc/sys/vm/dirty_background_ratio # for energy saving

Dirty Writeback sentisecs
echo 500 > /proc/sys/vm/dirty_writeback_centisecs # "normal mode"
echo 60000 > /proc/sys/vm/dirty_writeback_centisecs # for energy saving

I think that all these changes will only slightly reduce the current consumption, but in total, the optimization can give some good result.

PS To find out how to use our antennas for radio transmitting devices (in the case of low power), you need to read the laws of a particular country in the area. In our country, I can use external Wi-Fi antennas. I don't know how in other countries. Energy saving optimization occurs by improving the reception and transmission - the Wi-Fi transceiver should reduce the power if the reception and transmission is at the proper level.

cleverca22
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Sun Sep 26, 2021 1:56 pm

renice123 wrote:
Sun Sep 26, 2021 1:24 pm
for i in 0 1 2 3; do cpufreq-set -c $i -g ondemand; done
for i in 0 1 2 3; do cpufreq-set -c $i -g powersave; done
all 4 cores share the same clock source, so you only need to set it for one core

renice123
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Re: raspberry pi 3b+ lowering power consumption to absolute minimum

Sun Sep 26, 2021 2:05 pm

It is interesting! Thank you cleverca22. I also tried to play with the "distribution" of tasks on the cores, but it seems that I will have to study the documentation. In "theory" it would be possible to load processes to a particular kernel (I did this to optimize work with sound on the advice of sound service developers)

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