drakkkan
Posts: 7
Joined: Fri Aug 09, 2019 4:03 pm

the 5W - 6W raspberry

Wed Aug 28, 2019 11:06 pm

Hi there,

For some time, i tryed to figured out this pb but wasn't able. Some help please.

My raspberry takes just too much energy. The ammeter shows me 5,5W for idle for a fresh raspbian lite install (including power supply).
Processor seems burning when i let him too long :/ i also tried with another power supply (link below) that used 4,9W

- I try with a second brand new raspberry 3B+ and still 5-6W.

- 2 times, the idle power was at 2,9W but i had no idea how. At that time, all worked perfectly. Consumption stayed at 2,9W after rebooting. And as i reinstall raspian, my power rise up again to 5-6W.

OS : 2019-07-10-raspbian-buster-lite
Board : Pi 3B+
Supply power :
5,4W > S-TR-010
https://www.kubii.fr/14-chargeurs-alime ... 06218.html
4,9W > stontronics T6716DV
https://fr.farnell.com/raspberry-pi/t67 ... e%2Fsearch


So 2 questions:
> Is the post is right? I read an article where the normal consumption was 1,9W on idle. Oo
> What could i do to lower this power?



i share here some power consumption if it helps :

On 5,5W "mode"

Disabling wifi, hdmi, -0,1 W
Disabling USB/ethernet -2,7W

On 2,9W "mode"

Disabling wifi, hdmi => didn't tried
Disabling USB/ethernet -1,3W

hippy
Posts: 5969
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 1:45 pm

From my notes, a Pi 3B+ without USB devices attached would be expected to draw about 400mA when idle, 2W.

If the SoC is getting burning hot, is drawing over twice the power expected, it could be that you have damaged the Pi in some way.

But you seem to suggest you are measuring consumption "including power supply". You also say you saw 2.9W at some point. Perhaps that was with the Pi disconnected; the consumption of the power supply. Thus 2W + 2.9W = 4.9W which is roughly what you are observing ?

Perhaps clarify what you have, what you are measuring, and how you are measuring.

drakkkan
Posts: 7
Joined: Fri Aug 09, 2019 4:03 pm

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 4:12 pm

hi,

thx for the reply :)

My ammeter is installed between the 230Vac and my power adaptator 230Vac/5Vdc (what i called "power supply"). So the power consumed by the adaptator and the raspberry is measured. Good efficency adaptor seems close to 85% with a class 6.
> 4,9 W = RaspConsumption / 0,85
> RaspConsumption = 4,16W

"You also say you saw 2.9W at some point. Perhaps that was with the Pi disconnected; the consumption of the power supply. Thus 2W + 2.9W = 4.9W which is roughly what you are observing"
> The 2,9W measure already included the power adaptator.

"If the SoC is getting burning hot, is drawing over twice the power expected, it could be that you have damaged the Pi in some way."
> indeed. That why i try on a second brand new raspberry but same thing. I commanded it at the same time as the first one. So maybe they sold me two damaged raspberry. Or maybe I damage the second one while i test it (but i really dont see how as i was very carefull)

Here is the way i mesure:

230Vac > Ammeter > Power adaptator 5Vdc > raspberry

And this is the link of my ammeter :
https://www.perel.eu/products/view/?id=382030

hippy
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Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 4:56 pm

drakkkan wrote:
Thu Aug 29, 2019 4:12 pm
And this is the link of my ammeter :
https://www.perel.eu/products/view/?id=382030
I am not sure I would have much confidence in the accuracy of readings from an AC mains power meter for readings at the lower ends of what it would be expected to be used with but I may be underestimating its capabilities. It does claim +/-1% or +/-0.2W but I would want to calibrate it first.

The best way to determine power used by a Pi is by intercepting the positive lead of the supply from PSU to Pi with a current measuring multi-meter, or by powering it from a bench supply which has voltage and current displays.

W. H. Heydt
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Location: Vallejo, CA (US)

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 5:53 pm

Ammeters don't read power. They read current.

drakkkan
Posts: 7
Joined: Fri Aug 09, 2019 4:03 pm

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 6:05 pm

"Ammeters don't read power. They read current."
> it is a "multi" meter

"The best way to determine power used by a Pi is by intercepting the positive lead of the supply from PSU to Pi with a current measuring multi-meter, or by powering it from a bench supply which has voltage and current displays."
> i gonna try the multi meter way reading current. But before, i bought 0,01ohm resistance, i want to see if i can measure current this way. Have you got a good reference not to expensive of a bench supply?

hippy
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Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 8:00 pm

drakkkan wrote:
Thu Aug 29, 2019 6:05 pm
Have you got a good reference not to expensive of a bench supply?
Not particularly. A good bench supply should last a lifetime so, deprecated, it's not actually much no matter how much it costs.

But before worrying about that ... What problem are you actually trying to solve ?

drakkkan
Posts: 7
Joined: Fri Aug 09, 2019 4:03 pm

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 10:17 pm

"What problem are you actually trying to solve ?"
> my RPi 3B+ consumes 5W for a fresh installed raspbian lite. It seems far from the 400mA (2W) it is suppose to take. And i try to figure why.

drgeoff
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Joined: Wed Jan 25, 2012 6:39 pm

Re: the 5W - 6W raspberry

Thu Aug 29, 2019 11:31 pm

hippy wrote:
Thu Aug 29, 2019 8:00 pm
A good bench supply should last a lifetime so, deprecated,
@hippy

Typo or do you not know that the word you should have used is "depreciated"?

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Imperf3kt
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Location: Australia

Re: the 5W - 6W raspberry

Fri Aug 30, 2019 1:10 am

Anything plugged into your Pi? Keyboard, mouse, monitor, thumb stick? All these devices will draw a small amount of power as well which can add up.
Are you using wifi?

The official power supply is 12.5w with about 6w of that for usb devices, so the Pi alone using up to 6w isn't unexpected, though at idle it is indeed not normal.

The processor getting 'burning hot' isn't useful. My Pi SOC gets burning hot at 60°C, which is within spec. What does a temperature measure read?
55:55:44:44:4C
52:4C:52:42:41

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rpdom
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Location: Chelmsford, Essex, UK

Re: the 5W - 6W raspberry

Fri Aug 30, 2019 4:20 am

Imperf3kt wrote:
Fri Aug 30, 2019 1:10 am
The processor getting 'burning hot' isn't useful. My Pi SOC gets burning hot at 60°C, which is within spec. What does a temperature measure read?
Getting "burning hot", with nothing plugged in (including SD card) except power is useful. The SoC should not even get warm without having booted some sort of OS or code.

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Imperf3kt
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Re: the 5W - 6W raspberry

Fri Aug 30, 2019 6:51 am

rpdom wrote:
Fri Aug 30, 2019 4:20 am
Imperf3kt wrote:
Fri Aug 30, 2019 1:10 am
The processor getting 'burning hot' isn't useful. My Pi SOC gets burning hot at 60°C, which is within spec. What does a temperature measure read?
Getting "burning hot", with nothing plugged in (including SD card) except power is useful. The SoC should not even get warm without having booted some sort of OS or code.
Yes, but in this case, it is 'burning hot' at idle, not with nothing booting.
55:55:44:44:4C
52:4C:52:42:41

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RaTTuS
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Re: the 5W - 6W raspberry

Fri Aug 30, 2019 7:48 am

Code: Select all

vcgencmd measure_temp
will say how hot
and

Code: Select all

top
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

User avatar
rpdom
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Location: Chelmsford, Essex, UK

Re: the 5W - 6W raspberry

Fri Aug 30, 2019 9:03 am

Imperf3kt wrote:
Fri Aug 30, 2019 6:51 am
rpdom wrote:
Fri Aug 30, 2019 4:20 am
Imperf3kt wrote:
Fri Aug 30, 2019 1:10 am
The processor getting 'burning hot' isn't useful. My Pi SOC gets burning hot at 60°C, which is within spec. What does a temperature measure read?
Getting "burning hot", with nothing plugged in (including SD card) except power is useful. The SoC should not even get warm without having booted some sort of OS or code.
Yes, but in this case, it is 'burning hot' at idle, not with nothing booting.
Yes, but should be tested with no boot card or other media to see if the chip is damaged.

hippy
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Location: UK

Re: the 5W - 6W raspberry

Fri Aug 30, 2019 1:11 pm

drgeoff wrote:
Thu Aug 29, 2019 11:31 pm
hippy wrote:
Thu Aug 29, 2019 8:00 pm
A good bench supply should last a lifetime so, deprecated,
@hippy

Typo or do you not know that the word you should have used is "depreciated"?
Typo, or brain glitch. I'll put it down to the lateness of the hour after another long, hot, muggy day :oops:

hippy
Posts: 5969
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: the 5W - 6W raspberry

Fri Aug 30, 2019 1:23 pm

drakkkan wrote:
Thu Aug 29, 2019 10:17 pm
"What problem are you actually trying to solve ?"
> my RPi 3B+ consumes 5W for a fresh installed raspbian lite. It seems far from the 400mA (2W) it is suppose to take. And i try to figure why.
The problem is you are measuring power consumption in a way in which differs to how power consumption of a Pi board would normally be measured.

By measuring the consumption of the combined PSU plus board, with equipment which we don't know the actual accuracy of, it is not possible to say if what you are seeing is what you would be expected to see or not.

There is not necessarily a correlation between what the meter shows and what the Pi board itself is actually consuming.

drakkkan
Posts: 7
Joined: Fri Aug 09, 2019 4:03 pm

Re: the 5W - 6W raspberry

Fri Aug 30, 2019 5:09 pm

@hippy: Well, it sound like you were perfectly right!

=> I tried another way to measure the current. I used a 0,01 ohm resistance. The results are quite normal. Here they are :

with OS SD > 8,15mV for 0,02 ohm = 407 mA = 2,03W / Powermeter = 4,9W
4, 01mV for 0,01 ohm = 407 mA = 2,03W


without OS SD > 7,70mV for 0,02 ohm = 385 mA = 1,92W / Powermeter = 4,4W
3,85mV for 0,01 ohm = 385 mA = 1,92W

So to conclude, the problem came from too much parameter and random accuracy for my way to measure with my powermeter. But as i get sometimes 2,9V, i just think my powermeter just have a pb.
By the way, the measure with a 0,01 ohm are incredibly precise ! At first, i thought it was just luck xD

Thx people for your tips and your time :)
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