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Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 12:58 pm

Summary:
1) I wanted to buy an official RPi power supply but it browned out twice (red LED turned off) when I tested it with RPi 4B. Video link included.
2) There is a specification mismatch between these two: the RPi 4B requires at least 4.8615 V. The power supply guarantees voltage in the range of 4.655-5.4621 V.

This official Raspberry Pi document states, that the threshold, where Raspberry Pi will report an undervoltage error, is 4.63 V +/- 5%, which can be thus as high as 4.63 V * (100%+5%) = 4.63 V * 1.05 = 4.8615 V. In other words, if your power supply voltage can drop below 4.8615 V, there is no guarantee that Raspberry Pi will not report an undervoltage error.
https://www.raspberrypi.org/documentati ... /README.md

The same official document states: "For Raspberry Pi 4, we recommend our 3A USB-C Supply"
The official product brief of the "Raspberry Pi 15.3W USB-C Power Supply" states, that:
Output voltage: +5.1V DC
Load regulation: ±5% Line regulation: ±2%
Which means, the voltage can legally drop all the way down to 5.1 V * (100%-5%) * (100%-2%) = 4.655 V
https://static.raspberrypi.org/files/pr ... -Brief.pdf
4.655 V is less than 4.8615 V . So the specifications are mismatched. The power supply doesn't guarantee enough voltage to reliably operate Raspberry Pi 4B.

Youtube Video showing the brownouts - intermittent audio unfortunately, but enough to understand:
https://www.youtube.com/watch?v=CKmHprPG6Fw
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 1:54 pm

The PWR LED is also under software control, and blinks briefly before the watchdog reset mechanism is called.

Have you actually measured the voltage on the 5V pins on the GPIO header?
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 1:59 pm

The RED led going off during booting is NOT an indication of a power fail, as this LED is now totally under the control of the CPU it can be turned off under software control. If it really is a brownout indication you should see the brownout icon in the upper right corner of the screen appear.

from the boot problem sticky RPI4 section.
Unlike other RPI, on a RPI4 the power LED is fully under the control of a GPIO expander, and when booting Raspbian resets this IO expander so causing the PWR LED to blink off on reboot. On booting the bootloader enables it again. But if the PWR LED goes off (blinks) at any other time it means have an unfit power supply/power cable. in short, the PWR LED should be always on except for a very short time just before a reboot happens.
so if you don't get a dropout icon there hasn't been a dropout!

I also notice that in your argument you ignore voltage drops through the cable, however this is a big factor for real brownouts, and is the reason that the official power supply uses a thick cable, with a low internal resistance, different power supplies usually a much thinner cable.
To really measure whether this power supply is inadequate, you have to use an oscilloscope to measure whether the voltage that the RPI receives falls below 4.65 Volts. Basically how do you get the 5% accuracy of the under voltage detector, different types of detectors have been used in different models but their accuracy has never been officially specified, I use 1%. accuracy. but that's more of a rule of thumb.

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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 3:20 pm

You lost a $15 sale this way.

You have many pieces of great information on Raspberry Pi Documentation at https://www.raspberrypi.org/documentation/
I searched the info about red LED first there, if I didn't found I used google, with priority on Raspberry Pi Forums. The information I found back then was that the red LED simply indicated undervoltage. I don't remember where I found the information.

If your official documentation included the information that the red LED is more complex than simply undervoltage, I wouldn't reject your product. I was interested in a safe and reliable power supply. Now I bought a 5V 4.2A charger from Konfulon for $6 and I am satisfied with it so far. https://konfulononline.com/index.php?ro ... uct_id=267

Now I know the turning off of the red LED doesn't imply undervoltage.

I think I don't ignore voltage drops on a cable in my argument. No additional cable, which could cause additional voltage drop, was involved in my setup. The product "Raspberry Pi 3A USB-C Supply", which contains a USB-C male, was directly plugged into the USB-C female of the product "Raspberry Pi". The specification interface of the product "Raspberry Pi 3A USB-C Supply" is the USB-C connector. It has no other low-voltage interface which could be considered the specification interface. The cable is an internal, undetachable part of Raspberry Pi 3A USB-C Supply. Some power supply regulator chips compensate for the cable's internal resistance, where the voltage drop on the cable is predicted from the current draw.

I didn't measure the voltage on 5V GPIO as Mr./Mrs. jdb asked. That's a great, reliable and easy accessible way to obtain a measurement! I don't have the pinheader female however. To verify specification compliance however I would need a digital oscilloscope and set a trigger level to 4.8615 V. I don't have a digital oscilloscope. Or solder a custom circuit with a comparator and a pulse extender, to notice even a momentary dropout.

You still have a specification mismatch between official recommended Raspberry Pi 3A USB-C Supply and Raspberry Pi.

Raspberry Pi requires at least 4.8615 V for error-free operation according to Raspberry Pi Documentation
Raspberry Pi 3A USB-C Supply guarantees only 4.655 V according to its own specification.

I am disappointed that such a highly capable vendor as Raspberry Pi Foundation - who could integrate such a powerful computer (I use your Raspberry 4B 4G as the main development computer for the development of Sugar Palm Tree Translator, a neural network based natural language translator that learns from 6 GB 1 billion word corpus of English and is in production use) with so much efficiency (mine takes just 6W in normal usage and cost me just 75$) with so much miniaturization (credit card size), makes what I consider a serious beginner mistake: a specification mismatch between a device and it's recommended official power supply.
Last edited by Twibright Labs on Wed Nov 11, 2020 3:33 pm, edited 4 times in total.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 3:34 pm

We've sold millions of these supplies, I don't think one has ever failed in its job of powering a Raspberry Pi, so whilst your numbers are technically correct, you need to take in to account the chance of it happening.

The power supplies range is indeed a range, but the chances of finding one that can only supply the minimum value is very very low. - they usually produce 5.1 very solidly - they are a very high quality supply that we test very thoroughly. The chances of them combining that with a Pi where the *measuring* of the voltage is also at it limit is fantastically small. And note, the warning fires off when that limit is reached, but the Pi doesn't necessarily die at that point anyway. So, really, there is nothing at all to worry about here.

If you don't have a scope then the best way to tell if the voltage has browned out is to check dmesg for any undervolt warnings. The on board detector is quite quick to respond and can determine very short drops.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 3:37 pm

Your reported symptom is "red light blinks when the board is rebooted" - which I have explained is expected behaviour. I also note that your board works correctly after reboot.

Yet we somehow go from that (working) scenario to declarations of incompetence because you're comparing worst-case tolerances on the PSU with worst-case tolerances on the *undervoltage monitor*.

The monitor has no impact on board function other than a) providing indication to the user and b) temporarily disabling turbo mode (so clocks run at idle speeds, to reduce the possibility of brownout on a power supply that's at the margins of its current limit).

The Pi will work at voltages lower than the undervoltage detection operates at - otherwise there would be no point in having a monitor that does not also perform brownout reset.

Edit:
"Raspberry Pi requires at least 4.8615 V for error-free operation according to Raspberry Pi Documentation"
Where does the documentation state this?
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 4:07 pm

jamesh wrote:
Wed Nov 11, 2020 3:34 pm
We've sold millions of these supplies, I don't think one has ever failed in its job of powering a Raspberry Pi, so whilst your numbers are technically correct, you need to take in to account the chance of it happening.

The power supplies range is indeed a range, but the chances of finding one that can only supply the minimum value is very very low. - they usually produce 5.1 very solidly - they are a very high quality supply that we test very thoroughly. The chances of them combining that with a Pi where the *measuring* of the voltage is also at it limit is fantastically small. And note, the warning fires off when that limit is reached, but the Pi doesn't necessarily die at that point anyway. So, really, there is nothing at all to worry about here.

If you don't have a scope then the best way to tell if the voltage has browned out is to check dmesg for any undervolt warnings. The on board detector is quite quick to respond and can determine very short drops.
Your design approach seems different from mine. I dislike mating mismatching speficiations strongly and feel guilty, ashamed and afraid about it. You apparently use a different approach, some kind of probabilistic method where you have statistical distributions of power supplies and Raspberries and then draw pairs from these distribution and simulate the probability of a failure.

However I mated mismatching specifications too. When designing Twibright Ronja I used NE592 for the outdoor optical head which is specificied from -30 degC but later I realized NE592 is specified from 0 degC. Since a user inexperienced in electronics is the manufacturer, requiring hobbyists to source military parts would be a problem. I tried to redesign it in discrete transistors but it was too complex. It was never an issue and it actually ran in -25 degC once at my home.

You say "chances are [...] very very low", "the chances [...] is fantastically small". How low and small specifically? What data are these claims based on?

"I don't think one has ever failed in its job of powering a Raspberry Pi" - if this happens to a user, he may not be aware that it happened. And even if aware, he may not notify you about it.

Is there a way I can configure the red LED so that it indicates undervoltage only, even during bootup shutdown process?

What is the upper Operating Conditions supply voltage (instantaneous) of Raspberry Pi where proper function is still guaranteed?
And what is the Absolute Maximum Rating supply voltage (instantaneous) of Raspberry Pi, where absence of damage is still guaranteed?
What is the minimum (instantaneous) voltage, where proper operation of Raspberry Pi and all USB peripherals is still guaranteed, but the proper function of the undervoltage warning is not necessarily guaranteed?
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 4:11 pm

Twibright Labs wrote:
Wed Nov 11, 2020 4:07 pm
jamesh wrote:
Wed Nov 11, 2020 3:34 pm
We've sold millions of these supplies, I don't think one has ever failed in its job of powering a Raspberry Pi, so whilst your numbers are technically correct, you need to take in to account the chance of it happening.

The power supplies range is indeed a range, but the chances of finding one that can only supply the minimum value is very very low. - they usually produce 5.1 very solidly - they are a very high quality supply that we test very thoroughly. The chances of them combining that with a Pi where the *measuring* of the voltage is also at it limit is fantastically small. And note, the warning fires off when that limit is reached, but the Pi doesn't necessarily die at that point anyway. So, really, there is nothing at all to worry about here.

If you don't have a scope then the best way to tell if the voltage has browned out is to check dmesg for any undervolt warnings. The on board detector is quite quick to respond and can determine very short drops.
Your design approach seems different from mine. I dislike mating mismatching speficiations strongly and feel guilty, ashamed and afraid about it. You apparently use a different approach, some kind of probabilistic method where you have statistical distributions of power supplies and Raspberries and then draw pairs from these distribution and simulate the probability of a failure.

However I mated mismatching specifications too. When designing Twibright Ronja I used NE592 for the outdoor optical head which is specificied from -30 degC but later I realized NE592 is specified from 0 degC. Since a user inexperienced in electronics is the manufacturer, requiring hobbyists to source military parts would be a problem. I tried to redesign it in discrete transistors but it was too complex. It was never an issue and it actually ran in -25 degC once at my home.

You say "chances are [...] very very low", "the chances [...] is fantastically small". How low and small specifically? What data are these claims based on?

"I don't think one has ever failed in its job of powering a Raspberry Pi" - if this happens to a user, he may not be aware that it happened. And even if aware, he may not notify you about it.

Is there a way I can configure the red LED so that it indicates undervoltage only, even during bootup shutdown process?

What is the upper Operating Conditions supply voltage (instantaneous) of Raspberry Pi where proper function is still guaranteed?
And what is the Absolute Maximum Rating supply voltage (instantaneous) of Raspberry Pi, where absence of damage is still guaranteed?
What is the minimum (instantaneous) voltage, where proper operation of Raspberry Pi and all USB peripherals is still guaranteed, but the proper function of the undervoltage warning is not necessarily guaranteed?
I'd say the chances of the PS causing a brown out detection to be at one end of its specification range and the detector at the other to be millions to one.

Statistical modelling is how this is done all over the place for all different things. For example the MTBF of the SoC is over 20 years. But the only way to know that is by testing at above normal temperatures and statistical modelling, because we cannot wait 20 years to find out.

There really is NOTHING to worry about here.

Even under a very worst case (incredibly unlikely to happen), a brown out will not damage the Pi itself. It MIGHT cause an SD card corruption.

The undervoltage detector will always work.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 4:45 pm

jdb wrote:
Wed Nov 11, 2020 3:37 pm
Your reported symptom is "red light blinks when the board is rebooted" - which I have explained is expected behaviour. I also note that your board works correctly after reboot.

Yet we somehow go from that (working) scenario to declarations of incompetence because you're comparing worst-case tolerances on the PSU with worst-case tolerances on the *undervoltage monitor*.

The monitor has no impact on board function other than a) providing indication to the user and b) temporarily disabling turbo mode (so clocks run at idle speeds, to reduce the possibility of brownout on a power supply that's at the margins of its current limit).

The Pi will work at voltages lower than the undervoltage detection operates at - otherwise there would be no point in having a monitor that does not also perform brownout reset.

Edit:
"Raspberry Pi requires at least 4.8615 V for error-free operation according to Raspberry Pi Documentation"
Where does the documentation state this?
"On all models of Raspberry Pi since the Raspberry Pi B+ (2014) except the Zero range, there is low-voltage detection circuitry that will detect if the supply voltage drops below 4.63V (+/- 5%). This will result in a warning icon being displayed on all attached displays and an entry being added to the kernel log."

I understand it like this:
4.63V (+/- 5%) = 4.8615 V
warning icon plus log entry = undervoltage error
undervoltage error = not an error free operation
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 4:48 pm

jamesh wrote:
Wed Nov 11, 2020 4:11 pm

I'd say the chances of the PS causing a brown out detection to be at one end of its specification range and the detector at the other to be millions to one.
OK, what are the data suggesting that the chance is millions to one?
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 4:50 pm

I've cleaned the thread of some posts - if you have a problem with a post report it, don't comment on it.

With regard to error free operation, 4.65 is the level where the WARNING will go off. There is a percentage range of error on this, so it could fire as high as the 4.8 or whatever it was, but note, this is a WARNING that low voltages are being detected, and even if it warns at 4.8 it is still going to be alright, because you won't get actual error until probably below 4.6. If you took the range the other way, so the detector was only firing at 4.6-5%, then you might have more problems, but we have already taken that in to account when choosing 4.65. And those extra low voltages are not going to be produced by our power supply as that is out of it range of permitted values.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 4:51 pm

Twibright Labs wrote:
Wed Nov 11, 2020 4:48 pm
jamesh wrote:
Wed Nov 11, 2020 4:11 pm

I'd say the chances of the PS causing a brown out detection to be at one end of its specification range and the detector at the other to be millions to one.
OK, what are the data suggesting that the chance is millions to one?
The fact we've sold millions and you are the first person to comment on it?

I don't have figures, but then, neither do you! Where are your figures that the situation you are describing will ever actually happen?
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 4:55 pm

Twibright Labs wrote:
Wed Nov 11, 2020 4:45 pm
I understand it like this:
4.63V (+/- 5%) = 4.8615 V
warning icon plus log entry = undervoltage error
undervoltage error = not an error free operation
My car has a warning light that comes on when it is getting low on fuel. It doesn't mean that my car will stop working straight away, it is just advising me that I should think about adding more fuel.

The low voltage warning is like that. Your Pi will not start misbehaving the instant it drops below that fixed voltage level. Just it is getting borderline.
Unreadable squiggle

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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 5:00 pm

Look on it like this. There is a range of voltage provided by the PS - statistically it's a bell curve, with the vast majority of supplies in the middle at 5.1v. There is also a bell curve of the accuracy of the monitor. The intersection of those bell curves is when there might be a problem, but the medians of these curves is actually a long way apart, so the actual intersection is tiny. So the chance of it happening are also tiny. So if the chance of having a PS at the lower end of the scale is 10000:1, and the likelihood of the detector at the high end of the scale is 10000:1, then the probability of them both happening in the same system is 10000*`10000:1. Which is small.

AND, we have already considered the margins involved when we chose the 4.65v level for the warning. Which makes actual errors even more unlikely.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 5:04 pm

What's the specification of the 4 port 'charger/psu' you are using ?
And that 5Vis only at the USB port, not at the cable end since it is not integrated.
How does you cable alter the charger spec now?

I understand a miss-match on a PSU that works really well and I think is classed as guaranteed to work with the Pi4, but you now have an unknown match I think ?

Although I do like your heatsink solution, looks good.

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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 5:07 pm

Oh, I cannot add administrators (jdb) to my foe list? I feel contempt towards this whole forum and towards the whole Raspberry Foundation or Trading for setting up a forum like this. I consider this authoritarianism and abuse and unfair if administrators can perpetrate abuse towards users but users cannot put them on the foe list.

Being in such an environment is unacceptable for me - deleting my account here.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 5:14 pm

A little bit more information on the low power detection circuit on the Pi4/400 that I didn't know!

There is a range where the detection is guaranteed to fire, might fire, and wont fire. This is down to the PMIC, nothing to do with us.

0-4.52 Will fire
4.52-4.65 Might fire
4.65-5.1+ Won't fire

Since 4.52, the guaranteed detection point, is below our PS specification range, we are in the clear here, as before, there is nothing to worry about.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 5:18 pm

Twibright Labs wrote:
Wed Nov 11, 2020 5:07 pm
Oh, I cannot add administrators (jdb) to my foe list? I feel contempt towards this whole forum and towards the whole Raspberry Foundation or Trading for setting up a forum like this. I consider this authoritarianism and abuse and unfair if administrators can perpetrate abuse towards users but users cannot put them on the foe list.

Being in such an environment is unacceptable for me - deleting my account here.
Hmmm. So, the majority of people have been polite and answered your question in some detail. Even when asked, you haven't reported posts you were upset with. And yet you now regard those people with contempt?

Now you are going off in a huff because of posts that could have been deleted, had you only reported them.

And you know what is odd. One of our mods predicted this would happen from your first post. (Not jdb either). Which make me think you intended this to happen from your first post.
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 9:17 pm

Apparently there is a mathematical error in the first post

This from another user:
just to say he got his sums wrong: "5.1 V * (100%-5%) * (100%-2%) = 4.655V" should be 4.7481, he used 5V instead of 5.1V
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Re: Official power supply browns out with RPi 4B, voltage specifications mismatched

Wed Nov 11, 2020 9:21 pm

Also, in response to the OP changing their signature to this
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The admins verbally abuse. You defend yourself? Your post gets deleted while the abusive one stays. You cannot block admins or criticize their actions. You cannot delete your profile. I feel contempt towards this forum and the Raspberry Pi vendor.
I deleted one post from a non-mod that I felt was abusive, and, had any other posts been reported, I likely would have deleted that as well. However, I did not see any reports on other posts. You can criticize mod actions - that is what the report button is for, but don't do on the open forum please.

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