Sod Almighty
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Voltage warning troubles

Mon Jun 08, 2015 1:08 am

I just bought a new Raspberry Pi 2. The voltage warning appears when the voltage is 5.1v (according to my multimeter) and goes away when given 5.17v.

Surely 5.1 volts should be acceptable?

I don't want to disable the warning; but neither do I want crap on my screen. Is there some way I can calibrate this warning, or should I just return the board as defective?

ShiftPlusOne
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Re: Voltage warning is wrong

Mon Jun 08, 2015 1:21 am

Where are you measuring the 5.1v, how reliable is the multimeter and does it have a fresh batteries?

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 2:06 am

ShiftPlusOne wrote:Where are you measuring the 5.1v, how reliable is the multimeter and does it have a fresh batteries?
Hi. I'm measuring the 5.1v from the board where the power port is connected. I am aware that some (all?) Raspberry Pis have so-called "voltage measurement points", but I'm not interested in the voltages at various arbitrary locations on the board: I am interested in the supply voltage under load.

I don't know how reliable the meter may be. Lacking a magical device that can be relied upon to always output a known voltage, I know of no way to test it.

I have replaced the battery with a fresh one. I'm still getting the 5.1v reading.

klricks
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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:47 am

Sod Almighty wrote:
ShiftPlusOne wrote:Where are you measuring the 5.1v, how reliable is the multimeter and does it have a fresh batteries?
Hi. I'm measuring the 5.1v from the board where the power port is connected. I am aware that some (all?) Raspberry Pis have so-called "voltage measurement points", but I'm not interested in the voltages at various arbitrary locations on the board: I am interested in the supply voltage under load.

I don't know how reliable the meter may be. Lacking a magical device that can be relied upon to always output a known voltage, I know of no way to test it.

I have replaced the battery with a fresh one. I'm still getting the 5.1v reading.
Is the power warning (small colored box on top right of screen) on constantly?
What is the mA rating of the power supply?
What else is connected to the RPi?
Test at the fuse F1 to ground. The side closest to the edge of the board, (Or use test point PP1). That is power straight from the adapter (before the fuse).
Any other 5V on the board would be just as valid as long as the RPi is running. For example at the GPIO header pin 2 or 4.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

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rpdom
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Re: Voltage warning is wrong

Mon Jun 08, 2015 5:59 am

Test the voltage between ground and each side of the fuse in turn. It is possible that your fuse has a slightly higher resistance than it should and is dropping over 0.5V.

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 6:04 am

klricks wrote:What else is connected to the RPi?
A wireless keyboard dongle, some speakers, an ethernet cable, and a "PI supply switch" from http://www.pi-supply.com/product/pi-sup ... er-switch/
klricks wrote:Is the power warning (small colored box on top right of screen) on constantly?
It is on when the PI Supply switch is connected, and I am running OSMC, and it is not in idle power-save mode (dimmed screen). If I disconnect the switch, the voltage jumps to something like 5.17, and the warning goes away.
klricks wrote:What is the mA rating of the power supply?
It's an official Raspberry PSU by Stontronics, rated at 2 amps.

I had the option of buying a more powerful 5.25v PSU (from https://www.pi-supply.com/product/uk-mi ... 5v-1500ma/) but didn't trust it, so went for the official product.
klricks wrote:Test at the fuse F1 to ground. The side closest to the edge of the board, (Or use test point PP1). That is power straight from the adapter (before the fuse).
Any other 5V on the board would be just as valid as long as the RPi is running. For example at the GPIO header pin 2 or 4.
Actually, it would appear that the Pi 2 doesn't have any test points. I have, however, re-run the test from the fuse as suggested. The reading is now 4.85v. Oddly, the voltage from the port (that I was measuring before) is now also 4.85v. I'm confused.

Without the switch, I'm now getting 5.13v; rather than the 5.17 I was getting before.

I didn't make a mistake. The reading has changed, and I don't know why. Perhaps the meter is lying to me?

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 6:51 am

It would appear that the dirt-cheap and unnecessarily-long USB cable http://www.pi-supply.com supplied with the switch is dropping 0.31v, compared to the switch circuit itself which only drops 0.02v.

Reckon a shorter cable would solve the problem? Or do I need a gold-plated one or something?

Incidentally, the voltage keeps dropping the more I measure it. The most recent reading is 4.7v. This makes no damn sense.

klricks
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Re: Voltage warning is wrong

Mon Jun 08, 2015 12:58 pm

Sod Almighty wrote:It would appear that the dirt-cheap and unnecessarily-long USB cable http://www.pi-supply.com supplied with the switch is dropping 0.31v, compared to the switch circuit itself which only drops 0.02v.

Reckon a shorter cable would solve the problem? Or do I need a gold-plated one or something?

Incidentally, the voltage keeps dropping the more I measure it. The most recent reading is 4.7v. This makes no damn sense.
Are you sure the RPi was fully booted and running when you did voltage tests? Also the power used by the RPi can vary depending on what is running.
Bad connections in power circuits tend to heat up and get worse over time.
I am using a 5V 10A supply and still got a power warning until I made my own USB power cable. Got the micro USB end plugs off of ebay and soldered my own wires.

FYI - The RPi has many test pads all over the bottom side of the board for various things. They are labeled with PPx designations. The primary purpose of these was to allow automated testing during manufacturing. Somewhere on the forums is a list of functions of each.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 2:32 pm

klricks wrote:Are you sure the RPi was fully booted and running when you did voltage tests? Also the power used by the RPi can vary depending on what is running.
Pretty sure, yes. And the RPi was doing the same thing every time: sitting there in OSMC at the main menu.
klricks wrote:Bad connections in power circuits tend to heat up and get worse over time.
Except that the culprit here seems to be the USB cable (not a defective cable, just a reasonably long one); and therefore bad connections aren't the issue.
klricks wrote:I am using a 5V 10A supply and still got a power warning until I made my own USB power cable. Got the micro USB end plugs off of ebay and soldered my own wires.
You know, that's not a bad idea. I wouldn't try making an actual USB cable, because the signals degrade like hell if you use your own wires (I don't know why), but a power-only cable should be easy...
klricks wrote:FYI - The RPi has many test pads all over the bottom side of the board for various things. They are labeled with PPx designations. The primary purpose of these was to allow automated testing during manufacturing. Somewhere on the forums is a list of functions of each.
Hmm. I'll see if I can find that post.

Incidentally, I emailed the shop where I bought all this equipment (http://www.pi-supply.com) and his advice was "disable the warning"(!!)

He said "it is all working perfectly" and "we haven't said anywhere that it won't drop voltage" and "it is not even at a level to cause any issues". He advises, with a straight face, to add avoid_warnings=1 to the config.txt file. He takes no responsibility for the problem - indeed, does not even admit to there being a problem - despite the demonstrable fact that I am getting a power warning using only his equipment.

I advise everyone to think twice before buying from this guy.

ShiftPlusOne
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Re: Voltage warning is wrong

Mon Jun 08, 2015 2:35 pm

I wouldn't blame the product without first establishing that that's definitely the problem, but disabling the warnings is terrible advice.

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 3:17 pm

Here is a direct quote from the PI-Supply guy, that I just this moment received from him. Honestly, I have no idea what to say to this. It's like talking to a brick wall.
If you read any of the official documentation on the matter, it's not a problem until you get below 4.65 volts. Yours is at 4.8+ so is not an issue.

Most of the circuitry in the pi only needs 3.3v in fact, and the voltage is dropped to that level from 5v anyway.

The USB spec also allows for voltages down to 4.75 volts.

So what I'm saying is that it is not a problem if your device is seeing 4.8 volts. You don't seem willing to accept that fact, even though it is a published statistic from the manufacturers / designers.

Also, perhaps if you are worried you could try with a different USB cable like you said and see if that makes any difference? Do you have any other micro USB cables lying around you could test with?

I don't understand why you think that makes it "not fit for purpose"?

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 3:20 pm

Bear in mind that he had previously said "you shouldn't see the rainbow thing unless it's under 4.75v anyway".

The "rainbow thing" is appearing. Therefore, logically, the voltage is dipping below 4.75v.

ShiftPlusOne
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Re: Voltage warning is wrong

Mon Jun 08, 2015 3:25 pm

He hasn't said anything wrong there, it's just that you ARE seeing a voltage lower than 4.65v. It could be the cable, the fuse or anything else you have between the the supposed 5v source and the pi's 5v line. If you measure something that low at the actual supply output terminals while under load, then yeah, that's the problem. If you're seeing something near 5v on the output terminals and something much lower on the pi itself, the problem is elsewhere.
Sod Almighty wrote:The "rainbow thing" is appearing. Therefore, logically, the voltage is dipping below 4.75v.
4.65+/-$some% actually

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 3:29 pm

ShiftPlusOne wrote:He hasn't said anything wrong there,
Except that he refuses to accept that I'm getting a low voltage. And that this must, by definition, be his fault.
ShiftPlusOne wrote:It could be the cable, the fuse or anything else you have between the the supposed 5v source and the pi's 5v line. If you measure something that low at the actual supply output terminals while under load, then yeah, that's the problem. If you're seeing something near 5v on the output terminals and something much lower on the pi itself, the problem is elsewhere
What I have is PSU -> PI SWITCH -> USB CABLE -> PI.

All of the above are from pi-supply.com.

The voltage between the switch and the cable is 5.1v. The voltage between the cable and the PI is less than 5. And the rainbow box appears. Seems conclusive to me.

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 3:48 pm

"Is there anything else wrong other than the rainbow square? If not, then there isn't a problem is there?"
-- Aaron, www.pi-supply.com

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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:01 pm

Okay, that's a bit of an unfortunate attitude. The under-voltage warning is there for a reason.

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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:05 pm

Sod Almighty wrote:"Is there anything else wrong other than the rainbow square? If not, then there isn't a problem is there?"
-- Aaron, http://www.pi-supply.com
I have gone over to using a PSU with inbuilt power lead

http://swag.raspberrypi.org/collections ... wer-supply
Rather than negativity think outside the box !
RPi 4B 4GB (SSD Boot) RaspiOS64 ARM64
Asus ChromeBox 3 Celeron is my other computer...

ShiftPlusOne
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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:09 pm

Those are the ones we use at the office. Haven't had any problems, seems pretty solid.

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:11 pm

ShiftPlusOne wrote:Okay, that's a bit of an unfortunate attitude. The under-voltage warning is there for a reason.
Yes, thank you. That's what I figured. Warnings are generally there for a reason.

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:12 pm

fruitoftheloom wrote:I have gone over to using a PSU with inbuilt power lead
Oh, I have one with a built-in cable. That exact one, in fact. But I'm using this clown's switching circuit as well, and that's causing voltage drops and rainbow warnings. And he just will not admit there is a problem.

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:15 pm

More nonsense from the seller: "No it doesn't mean there is a problem. It is a software based warning from the GPU; the OS and desktop GUI don't even know about the rainbow square. It is just that - a warning."

Why would a warning from the GPU carry any less weight than one from the OS?

Why is a warning assumed to be unimportant?

Why won't this guy take responsibility for his own hardware?

shawaj
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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:22 pm

Have you perhaps thought that it might be you with the negative attitude?

I have been trying to help you from your very first email, and instead of answering my genuine questions, you just ignore those and hurl abuse and aggravation at us. Not exactly a productive attitude.

I can't help you diagnose a problem without your help unfortunately.

If you could help us out here by trying a different PSU, different USB cables etc etc then we can actually work out what the problem is.

You have already said that the voltage drop accross the device is only 0.02v - and you then go and say it is causing excessive voltage drop? This seems a bit strange to me, and not a logical conclusion.

It may well be the USB cable - but we need you to swap that out to check if that is the problem.

Please help us to help you before defaming us on a public forum with your libelous comments :-)
Support The MagPi by purchasing printed copies from one of our retailers - http://themagpi.com/en/buy

Please share with anyone who is interested!

shawaj
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Re: Voltage warning is wrong

Mon Jun 08, 2015 4:24 pm

P.S. if you do not have another PSU to try, please let me know and we will even send you one to test with!
Support The MagPi by purchasing printed copies from one of our retailers - http://themagpi.com/en/buy

Please share with anyone who is interested!

Sod Almighty
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Re: Voltage warning is wrong

Mon Jun 08, 2015 5:21 pm

Hi Aaron, and thank you for joining me on this public forum. I'm not sure what you consider "libel", however, as I am not aware of having claimed privileged access to defamatory information. I have simply quoted you, and explained the situation as it has appeared to me. This does not constitute libel where I live.

As you are well aware, I have already narrowed the voltage issue to the usb cable. And, as already explained, the problem persisted when I connected my own (reasonably long) usb cable. This leads me to conclude that either (a) all long usb cables cause this problem (at least when combined with the switch circuit and official PSU); or (b) the Pi is incorrectly reporting a low voltage.

I fail to see how a replacement PSU would help to diagnose the problem. The PSU I am using is, as you know, an official one; and outputs a consistent 5.17 volts under load, according to my multimeter. I guess it would be helpful to test the PSU and USB cable together in the absence of the switch circuit, but lacking a female-micro-USB-to-female-USB-A adapter, this is not possible.

I admit that the precise nature of the problem is not known; and further tests may help. What has me irate, however, is your flat refusal to accept that a low-voltage warning constitutes a problem in and of itself. If you were to approach the matter with the attitude of "yes, there is a problem, now let's figure out what it is", that would be fine. But throughout our communications, your position has unwaveringly been one of disbelief and a refusal to accept the situation.

The plain, undisputed (except by you) facts of the matter are: (1) there is no problem when the switch and the USB cable are removed; (2) a voltage warning appears when they are connected; (3) a low-voltage warning without question DOES constitute a problem; and (4) all the components and cables in use were sold by you.

Once you accept these self-evident facts, you will find me much more amenable.

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Re: Voltage warning troubles

Mon Jun 08, 2015 5:31 pm

Just a quick heads up that if this thread becomes more of a problem, it will be locked. Maybe it should've been already.

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