raspberry pi power

[venderbroeck]

I recieved my raspberry Pi a few days ago and have been trying to set it up ever since.
At first everything was looking great, I bought a new sd-card from adata and installed raspbian wheezy.
After connecting the lan cable, the first problems started to arise. It would crash suddenly at random moments presenting me with nothing but a blank screen.
I had been using a usb power pack, and it turned out that with the ethernet cable, hdmi, keyboard and mouse the supply voltage dropped below 4.3 volts at times. The powerpack is rated at 2.1A so this was a little disappointing. I then switched to a powered usb hub with a 2A adapter, but this also caused voltage drops and crashes. I decided to completely overkill it and feed the usb hub with a ATX psu.
This thing is rated 20A at the 5v rail. Imho this should be enough, but voltage levels still drop below 4.8v
It is my understanding that the raspberry only operates at a narrow band of supply voltages, and anything below 4.8v will cause crashes, and anything above 5.1v will cause overheating.
I think its a miracle anyone got the thing working right with Phone chargers and the like. O_o
My htc Phone charger is rated at 1a and it outputs somewhere around 4.1-4.3 volts with my raspberry connected.
Why does my raspberry crash on a 20 amp power supply? could the usb hub be causing problems for me?

[venderbroeck]

I've ruled out the usb hub.
I connected a micro usb cable directly to a molex connector of the PSU.
The raspberry is now running with nothing attached but the sd-card.
I read 5.1 volts at the molex connector, but at the tp1 and tp2 points I read 4.8 volts.
With everything attached it drops to 4.6 and below.
I used a short piece of cable to connect to the molex.

Does anyone have an idea of what's going on? Is my raspberry faulty?

[rurwin]

Can you measure the voltage across FS3 with the power on, and the resistance of FS3 with the power off? My guess is that it has a higher resistance than it should.

[venderbroeck]

Where is FS3 located? I can't seem to find it.
Also I tried powering it via GPIO pin 2 and 6.
On the powerpack this still results in low voltages, but on the atx psu it now reads 5.1v with nothing attached and 5.0 volts with everything attached.

It still crashes when running apt-get update...
Frustrating pieces of hardware these raspberry pi's

[Wheel_nut]

F3 (not FS3) is the Polyfuse and is on the underside of the board, below the MicroUSB connector. It would appear that the Polyfuse has a higher resistance than normal.

What Rev # is your Board and where was it made?

It is possible that your ATX Power Supply is not as smooth (free of ripple) as it could be if you are still having problems feeding that to the GPIO pins. A better solution would be to use a POWERED USB Hub and back-feed the RPi.

[rurwin]

I think you have two problems - F3 and the USB cable. Both have a high resistance.

[venderbroeck]

I will measure the resistance of f3 first then.
I believe my pi is a type b rev 1.0 one. It has 512 mb ram. I will check where it was manufactored when I get home.

The atx supply is an unbranded one, so that could be. I will try a higher grade corsair one. Backfeeding means using the gpio right? Does that bypass the micro usb power components? I will also try a powered usb hub and a stabilised power supply we have at home, if that doesn't work.

I will post my findings when I get home.

I did try a few different usb cables with no noticable improvement.

[venderbroeck]

I've measured the resistance of the f3 fuse. It's about 0.6 ohm on my multimeter.
I will now try different psu setups, and post my findings.

edit: I've also read about problems with the f1 and f2 fuses. My raspberry doesn't seem to have these, but has a yellow smd next to the act led instead. I can't make out what it says on the smd, but is says c32 on the print. Is this some kind of power regulator?

My raspberry was made in china.

[mahjongg]

You have a revision 2 board (the 512MB RAM is a dead giveaway), and indeed two USB polyfuses F1 and F2 were removed on the rev 2 board, because they caused similar misery, only much more so.
C32 is just a local (tantalium) capacitor for decoupling the 5V, located near the USB port.

0.6 Ohm is on the high side, it would account for a voltage drop of about 0.3Volt, which is indeed too much. 5.0 - 0.3 = 4.7 V which is a bit low. Dropping even lower when the PI + USB devices draws more than 500mA.

The resistance of the polyfuse could have been caused by an earlier short circuit current flowing through them, but also polyfuse makers often underestimate the resistance of their devices in their datasheets, and every once in a while one may have even more resistance than what is said to be the maximum in the datasheet. Still excessive power drops may also sometimes (partly) be caused by cheap mini-USB cables that are only rated for data exchange, not for powering devices.

[venderbroeck]

Allright, so what is the best course of action for me then?
Should I return the board, or attempt to replace the polyfuse myself?
Does powering it via the GPIO header bypass said polyfuse?
I can live with powering it via GPIO pins.

I bought the raspberry to learn a little more about Linux and to try and create a portable wifi hdd.
I originally planned to use my Lenmar powerport wave6600 for this, but although it has a 2.1a port it doesn't seem to provide nearly enough voltage under load, even when connected to the GPIO pins. Are there any known good powerpacks, that can power the Pi for any substantial amount of time?

Or better yet, is there any way to stabilise/improve the voltage output from my current powerpack? I'm not new to soldering my own circuitry, or electronics in general, but I never designed my own circuits.

[Wheel_nut]

I agree with Rurwin that you seem to have both the High Resistance F3 problem AND the High impedance USB Cable problem.

I believe that powering through the GPIO pins bypasses the F3 Polufuse but I haven't seen the schematics so can't be sure.

Backfeeding is powering the RPi from a Powered Hub through its upstream cable to one of the two USB Ports which have no fuses.

You need a Powered Hub with a 2A or better PSU and beware that most of the cheap hubs sold on eBay come with a 400mA psu even if the listing says 2A or 3A. I use a 2.1A PSU and a 7 Port USB Hub and connect all USB devices to the Hub, thus minimising the load on the upstream cable

[venderbroeck]

I have tried a few ways of powering the pi without result.
The last thing I tried was a very stable PSU used by my father to experiment with electronics.
I connected it directly to the GPIO pins, and it booted up fine with only a keyboard, lan, and hmdi connected. After half a minute the screen went blank again. All that time the voltage had been a perfect 5.1v. If the pi isn't running on this kind of PSU, then there's no way it's ever going to run on a Nokia adapter or something like that.

I have also tried different monitors and sd-cards.
This leads me to conclude I must have hit the jackpot in the shitty component lottery. Something must be overheating somewhere, and on top of that, the f3 fuse also is of bad quality. Unless anyone here has a brilliant idea for me to try, Í think I'm going to try and get it replaced.

At any rate, thank you all for the help provided .

edit: I read that alot of raspis are struggeling with the f3 fuse. One could wonder why that fuse is used in the first place, when it's obviously causing alot of trouble for alot of people. A design flaw imo, there must be a better way to power this thing.

[Wheel_nut]

It would seem that you have a defective unit ... or at least, your problem is not related to supply Voltage.

Time to call your supplier for an RMA Number.