ilfugiuliopascal
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Max power supply voltage

Sat Jun 01, 2013 3:14 pm

Hi everyone,
I made my own power supply unit and I measured 5.70-5.75 V between the test points on the pi. Is it too high? Actually my pi works fine, but I fear long-term problems. What do you think about it?
Thank you!

klricks
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Re: Max power supply voltage

Sat Jun 01, 2013 4:27 pm

That's a bit high.
Can you post a schematic of your power supply?
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

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mahjongg
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Re: Max power supply voltage

Sat Jun 01, 2013 5:17 pm

The allowed voltage range is the normal one (for 5V logic) 5.0V ±5%
so its a the range between 4.75V and 5.25V.
Note that the lower limit of 4.75V is more a matter of many USB devices not working below that value than it is that the PI itself is that sensitive, especially as much of it (including the ethernet/hub chip, and the SD-card) is working from 3,3V through a regulator on board of the PI that will keep working even with say 4.0V.

Also note that many 5V logic devices will be damaged by voltages of 6.5V or higher! Therefore there is a protection device on the PI (D17) that will short the 5V supply if about 6.0V is supplied! Then the (poly)fuse will blow out to protect D17 from burning up! If you do not power the PI through the normal micro-USB port then you are actually bypassing that fuse!

there is a section of the PI Wiki at http://elinux.org/RaspberryPiBoard dedicated to boot problems like this.

ilfugiuliopascal
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Re: Max power supply voltage

Sun Jun 02, 2013 9:32 am

Thank you for your answers. This is my schematic.
VCC1= 11.1V 1000mAh
C1= 2200uF
C2=470uF
C3,C4=100nF
R1=1kohm
R2=100ohm

The problem is that pi's voltage changes as I connect USB devices (webcam,wifi), ethernet, or GPIOs. So I considered to replace R2 with a linear trimmer in order to adjust it depending on the circumstances. What do you think about this?

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Burngate
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Re: Max power supply voltage

Sun Jun 02, 2013 10:25 am

The problem may be the 7805 regulator, depending on the size of its heatsink.
As you're no doubt aware, the 7805 is dropping the 11v to ~5.5v while passing >700mA, so dissipating ~4W. If it gets too hot it'll start to shut down, so dropping the o/p voltage

btidey
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Re: Max power supply voltage

Sun Jun 02, 2013 10:41 am

You may want to check out using a switching regulator for this type of application. Do a search for UBEC on eBay and you can find 5V 3A UBEC modules very cheap.

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mahjongg
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Re: Max power supply voltage

Sun Jun 02, 2013 1:54 pm

or simply use a car sigar plug adapter with an USB output, way cheaper than an UBEC (less than $5,-) if you buy it at the right place, and there are many more places you can buy it from than for model airplane gear, also no need for mail costs. And you can directly plug in an microUSB cable. No need to hack the cable to the ubec output wires (don't plug in an ubec to the GPIO, its not safe, as you are bypassing the PI's fuse0.

as for the cigar plug, it normally opens up easy, (try unscrewing the tip) and you can connect the + of your battery to the "tip" wire, and the - to the "side wing" wire.

ilfugiuliopascal
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Re: Max power supply voltage

Sun Jun 02, 2013 6:18 pm

Thank you very much for your answers. I did not know the existence of the UBEC 5V 3A and I have just ordered one. At the same time the idea of using a car cigar plug sounds great and I'll try it in the future.
Unfortunately I must use a 7805 for this project. The pi and the things connected to it should take no more than 700-800mA, I hope. This is my heatsink. It does not heat too much.

Do you think the previous schematic, with the trimmer, could work or do you consider it really an impractical solution?

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mahjongg
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Re: Max power supply voltage

Sun Jun 02, 2013 10:24 pm

trimmer should not be necessary, even a lowly 7805 should be able to keep its output within 5%.
with the trimming you are really just battling the symptoms instead of curing the problem!

I assume that either the cable from the 7805 to the PI is of too low quality, or you managed to degrade your polyfuse so that it isn't a non-issue, but has become an issue. That is it probably has a non insignificant resistance now.
Don't try to measure either the cable or the fuse's resistance with an ohm-meter, the resistances will probably still be too low for a cheap meter, instead try to measure the voltage over (on of the leads of) the cable and over the polyfuse. There should not be a voltage more than 0.01 Volt over each when running the PI.

FaceAche
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Re: Max power supply voltage

Mon Jun 10, 2013 4:57 am

Hi there, my first post!

I'm about to get a Model B, and had a questions about the power (didn't want to start a new thread for such a noob question).

Anyway, i'd like to use a Wifi dongle, and understand that 700mA won't provide enough juice. Will a 5.2V 2.4A power supply work okay?

Thanks in advance.

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FTrevorGowen
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Re: Max power supply voltage

Mon Jun 10, 2013 7:18 am

FaceAche wrote:Hi there, my first post!

I'm about to get a Model B, and had a questions about the power (didn't want to start a new thread for such a noob question).

Anyway, i'd like to use a Wifi dongle, and understand that 700mA won't provide enough juice. Will a 5.2V 2.4A power supply work okay?

Thanks in advance.
As long as it doesn't produce more than ~5.5V "off-load" and is (well-)regulated could be O.K. (As I understand things the Pi has "crowbar" over-volatage protection that triggers at ~6V. ) It's probably worth checking http://elinux.org/RPi_VerifiedPeripherals to see if anyone has already tried the unit you're thinking of. FWIW, if you're curious about the "gory details" of PSU loading issues pop over to http://www.cpmspectrepi.webspace.virgin ... plies.html within my webpages.
Trev.
Still running Raspbian Jessie on some older Pi's (an A, B1, B2, B+, P2B, 3xP0, P0W) but Stretch on my 2xP3A+, P3B+, P3B, B+, A+ and a B2. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

Fuintur
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Re: Max power supply voltage

Sun Jan 19, 2014 4:43 am

Hello,

last time I used my raspberry, I tried to plug and configure a wifi antenna into it. I got quite far (it was going well), but then I plugged a usb hub into one of the raspberry usb ports, and I powered it, by mistake, with a 9V adapter. The wireless keyboard/mouse antenna I had plugged into the hub got burned (not with actual fire, but it was broken), and I never managed to have my raspberry recognize any mouse/keyboard anymore. I can, though, power the raspberry through any of the usb ports as usual, and it will switch on, and display the whole raspbian bootload sequence and even desktop.

Is it a matter of changing the F3 fuse and/or D17, or did I lose my raspberry, since being powered from the USBA port the overvoltage bypassed the microusb protections (as I understood from what mahjongg said)?

Is there ANY fix?

Than you!

Fuintur
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Re: Max power supply voltage

Sun Jan 19, 2014 3:58 pm

From what I have understood looking at the schematics ( http://www.raspberrypi.org/wp-content/u ... s-R1.0.pdf ) a1, a4, b1 and b4 (the vcc and ground pins for each of the usb A ports), feed into the board's 5V voltage through the F1 and F2 fuses (that I cannot see anywhere, so I guess they're inaccesible), and on another branch feed into the USB LAN 9512 IC PRTCTRL 2 and 3 throught the D11 BAS16 and D10 BAS15 diodes (that are nowhere to be seen neither).

Did I burn those unseen diodes and fuses? Or on a worse scenario, did I break USB LAN 9512? If so, how come I can still power my raspberry backfeeding through the USB A ports, and it will boot normally?

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Burngate
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Re: Max power supply voltage

Sun Jan 19, 2014 4:52 pm

If you can't see F1, F2, D10 & D11 then you've provably got a Rev.2 Pi. The biggest clue is the mounting holes on Rev.2 but missing on Rev.1
(If you've not got mounting holes, you may have one of the later Rev.1 Pis where the fuses were replaced with 0Ω links)

For Rev.2, you need to look at http://www.raspberrypi.org/wp-content/u ... .2_027.pdf
D10 & D11 are indeed missing, but more to the point, so are F1 & F2

Quite how the Pi survived isn't clear, but it does sound like the 9512 suffered terminally
Perhaps the over-voltage clamp (D17) protected the main SoC, or maybe the main Pi Psu pulled current backwards through F3
Quite possibly the 9512 didn't like whatever the hub put on its data lines.
It may have survived enough for you to SSH into it over the RJ45. If not, you're out of luck.

mattyd24
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Re: Max power supply voltage

Mon Jun 16, 2014 9:02 pm

Would my pi work with a regulated 4.6v supply?
Just a 12 year old geek...

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Burngate
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Re: Max power supply voltage

Tue Jun 17, 2014 9:54 am

4.6v is rather low.

Below 4.75v USB peripherals aren't guaranteed to work - and that's at the USB sockets, after the poly-fuse and the power supply cable.
The Pi itself may work, since most of it runs off 3v3 after the first regulator, and so is somewhat isolated.

Why do you not want to use a 5v supply?

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mahjongg
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Re: Max power supply voltage

Tue Jun 17, 2014 9:56 am

mattyd24 wrote:Would my pi work with a regulated 4.6v supply?
No! 4.75V is the minimum, and then we ignore possible voltage losses in the power cable and polyfuse, so 4.85V is a more practical lower limit.

mattyd24
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Re: Max power supply voltage

Tue Jun 17, 2014 4:51 pm

mahjongg wrote:
mattyd24 wrote:Would my pi work with a regulated 4.6v supply?
No! 4.75V is the minimum, and then we ignore possible voltage losses in the power cable and polyfuse, so 4.85V is a more practical lower limit.
Thank you!! :D
Just a 12 year old geek...

mattyd24
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Re: Max power supply voltage

Tue Jun 17, 2014 4:57 pm

Burngate wrote:4.6v is rather low.

Below 4.75v USB peripherals aren't guaranteed to work - and that's at the USB sockets, after the poly-fuse and the power supply cable.
The Pi itself may work, since most of it runs off 3v3 after the first regulator, and so is somewhat isolated.

Why do you not want to use a 5v supply?
I would not like to use a 5v supply as I found 4 1.2v rechargeable AA's with 2200mah for a project I'm making that would use 1 led, 1 button and the camera module. The problem is that the 4 batteries won't provide enough voltage for the pi, any ideas?

Another option was a 9v battery but I'm not sure if that would be able to provide enough power
Just a 12 year old geek...

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redhawk
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Re: Max power supply voltage

Tue Jun 17, 2014 6:01 pm

Use a buck step-up or step down regulator that way you can ensure the Pi gets the required voltage.
So even if say 3xAA produces less than 5v a step up buck converter would convert this into regulated 5v providing the cells can maintain required current drain.

Richard S.

drgeoff
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Re: Max power supply voltage

Tue Jun 17, 2014 6:24 pm

mattyd24 wrote:
Burngate wrote:4.6v is rather low.

Below 4.75v USB peripherals aren't guaranteed to work - and that's at the USB sockets, after the poly-fuse and the power supply cable.
The Pi itself may work, since most of it runs off 3v3 after the first regulator, and so is somewhat isolated.

Why do you not want to use a 5v supply?
I would not like to use a 5v supply as I found 4 1.2v rechargeable AA's with 2200mah for a project I'm making that would use 1 led, 1 button and the camera module. The problem is that the 4 batteries won't provide enough voltage for the pi, any ideas?

Another option was a 9v battery but I'm not sure if that would be able to provide enough power
The easy way is just to buy one of those 'powerbank' things intended to give extra operating time to phones and tablets. They have a built-in battery that charges from a 5 volt supply and electronics to deliver 5 volts out. Lots to choose from on fleabay.

hugorincong
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Re: Max power supply voltage

Thu Jul 23, 2015 8:04 pm

By error I pass 7.4v to the raspberry, now don't turn on, there is a way to save the board?

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DougieLawson
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Re: Max power supply voltage

Thu Jul 23, 2015 11:41 pm

hugorincong wrote:By error I pass 7.4v to the raspberry, now don't turn on, there is a way to save the board?
NO!
Note: Having anything remotely humorous in your signature is completely banned on this forum.

Any DMs sent on Twitter will be answered next month.

This is a hippy & doctor free zone.

shrawanraina
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Re: Max power supply voltage

Mon Dec 18, 2017 5:46 pm

I have an old ASUS 6V-2A charger (form first gen nexus tab). I understand that it is beyond the recommended voltage but I want to know what will happen if I use that to power the Pi3?

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mahjongg
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Re: Max power supply voltage

Mon Dec 18, 2017 6:55 pm

shrawanraina wrote:
Mon Dec 18, 2017 5:46 pm
I have an old ASUS 6V-2A charger (form first gen nexus tab). I understand that it is beyond the recommended voltage but I want to know what will happen if I use that to power the Pi3?

Don't do that!!!


In short you will blow up your PI!

all RPI's except the zero (w) have an overvoltage protector (TVS) diode that will short the power on the +5V line if it detects 6.0V or more, if you are lucky this will blow up the polyfuse fast enough so that the rest of the logic is not damaged.
If you bypass the fuse (power through the GPIO header) then you might be able to blow up (burn out) the TVS diode, this might either result in all logic blown, or only the TVS blown, shorting the 5V line to GND.

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