User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

voltage and polyfuse

Thu Jun 07, 2012 9:52 pm

I"ve had my pi for 4 days this morning, ran deb the first, arch the second and the armed slack yesterday. First 2 days fiddled with a powered hub and had all sorts of tries at using a wireless dongle but gave up. Yesterday I had good performance with slack and wired internet connection. Last night I tried using the powered hub again to attempt configuring wireless and lost the ability to boot. and had the pwr led only symptom. I let it cool an hour or so and had a successful boot but nothing plugged in so shutdown connected periphials but no more booting, just pwr led and once or twice faint green led flicker.

This morning no boot and only pwr led. I have used a good sd, card with arch on it, not the one I shut down on last night. I'm using a blackberry 5V 500mA plug

When I had my first boot failure last night the cpu had gotten very hot to touch as well as the capacitor and voltage regulator right next to it and I had 3.5V across TP1 and 2 I don't remember the resistance across F3 precisely but .243 ohms sticks in my mind.

This morning after boot failures I have 3.5V across TP1 and 2. The resistance across F3 is 1.4 ohms.

I don't understand enough about this to say more than I did have power back from the (dodgy?) hub to pi when it was connected I suspect this may have something to do with the problem.

After 12 hours waiting I expect the damage to be permanent in which case its either toss it or try to wire in a power supply to bypass the polyfuse if that is the problem.

Perhaps someone on the list can make a suggestion. Should I wire to each side of the polyfuse. Could I, for example, make up a little circuit with a regulator cap and replaceable fuse and connect there?

After writing this I had a thought to check the voltage from TP1 to each side of F3. Using the 5V 500mA blackbery charger I had 3.46V on the sdcard side and 3.76V on the outside. With a samsung 5V 1A phone charger I had 4.06V to the sdcard side and 4.55V to the outside.

Measuring voltage from each side of the capacitor to TP1 and 2 I have 4.01V

edit by moderator: corrected fuse numbering to prevent confusion.

User avatar
mahjongg
Forum Moderator
Forum Moderator
Posts: 12339
Joined: Sun Mar 11, 2012 12:19 am
Location: South Holland, The Netherlands

Re: voltage and polyfuse

Fri Jun 08, 2012 1:27 am

Polyfuses can take a very long time to completely recover from a "trip", sometimes days, even weeks, in fact in a sense they never get completely the same, but if they get down to say 3 Ohm (for the USB polyfuses F1 & F2) or 0.2 Ohm for the input polyfise F3 on the back of the board you can say they are "cured".
If they are, and you are still measuring less than 4.75 V between TP1 and TP1 I would search the problem elsewhere, maybe too thin wires in the "power cable", or you are using a cheap charger that has a label "5V 1A", but in fact drops half a volt when drawing just 400mA.

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4258
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: voltage and polyfuse

Fri Jun 08, 2012 6:45 am

My figures (even fresh from the factory) are higher than that. F1 & 2 are around 6-7 ohm, and F3 is 0.5-0.6 ohm.

It works at that, but it is marginal.

tufty
Posts: 1456
Joined: Sun Sep 11, 2011 2:32 pm

Re: voltage and polyfuse

Fri Jun 08, 2012 7:02 am

rurwin wrote:My figures (even fresh from the factory) are higher than that. F1 & 2 are around 6-7 ohm, and F3 is 0.5-0.6 ohm.

It works at that, but it is marginal.
Mine's just arrived (thanks Mark). Measured direct out of the box -
F3 : 0.4Ω
F1 : 5.3Ω
F2 : 7.2Ω

So, testing, using the Raspbian "pisces" image as ITBOK.

The situation is bad. With a "no name" 0.7A supply, and *even with no devices attached*, it won't boot. I wasn't intending to use that supply anyway, just thought I'd give it a go. That sucks, because a 0.5-0.7A wall wart is pretty much what the majority of people are going to be trying to use.

With a name-brand 2.1A supply, it boots fine. I've tried it with the following keyboards : Matias Tactile Pro (internal hub, rated at 50 + 50 mA), Apple A1048 (the "white & perspex" one - again, internal hub, rated 50 + 50) and Apple A1243 ("aluminium & chiclets", internal hub, 50 + 50).

I've not tried iMate + ADB "Extended" keyboard yet. That might well blow the power budget.

It's all a bit academic for the moment anyway, because I'm not going to be connecting keyboards or any USB devices for awhile yet.

Simon

edit by moderator: corrected fuse numbering to prevent confusion.

User avatar
Grumpy Mike
Posts: 914
Joined: Sat Sep 10, 2011 7:49 pm
Location: Manchester (England England)
Contact: Website

Re: voltage and polyfuse

Fri Jun 08, 2012 9:56 am

tufty wrote:
rurwin wrote:My figures (even fresh from the factory) are higher than that. F2 & 3 are around 6-7 ohm, and F1 is 0.5-0.6 ohm.

It works at that, but it is marginal.
Mine's just arrived (thanks Mark). Measured direct out of the box -
F1 : 0.4Ω
F2 : 5.3Ω
F3 : 7.2Ω
Actually on my board the main power fuse is labeled F3 not F1.
After about a two weeks of light use I get
F1 6.4Ω
F2 6.0Ω
F3 0.4Ω

I know poly fuses are in the USB's data sheet as an example design but they are not very good in general for use in this situation. I would never have designed them into a USB power system.

User avatar
walney
Posts: 233
Joined: Wed Nov 30, 2011 6:57 pm
Contact: Website

Re: voltage and polyfuse

Fri Jun 08, 2012 10:08 am

tufty wrote: Mine's just arrived (thanks Mark). Measured direct out of the box -
F1 : 0.4Ω
F2 : 5.3Ω
F3 : 7.2Ω

So, testing, using the Raspbian "pisces" image as ITBOK.

The situation is bad. With a "no name" 0.7A supply, and *even with no devices attached*, it won't boot. I wasn't intending to use that supply anyway, just thought I'd give it a go. That sucks, because a 0.5-0.7A wall wart is pretty much what the majority of people are going to be trying to use.
In the (short) time that I had it :? it worked fine with a 1.0A HP TouchPad wall wart. I succeeded in getting things up and running with a Belkin F8T013 bluetooth dongle plugged in directly (I don't own a powered USB hub), paired with a TouchPad BT keyboard and all was dandy... until I gave it to Simon. ;)

tufty
Posts: 1456
Joined: Sun Sep 11, 2011 2:32 pm

Re: voltage and polyfuse

Fri Jun 08, 2012 10:20 am

Grumpy Mike wrote:
tufty wrote:
rurwin wrote:My figures (even fresh from the factory) are higher than that. F2 & 3 are around 6-7 ohm, and F1 is 0.5-0.6 ohm.
Woops, my bad. Transcription error there.
walney wrote:In the (short) time that I had it :? it worked fine with a 1.0A HP TouchPad wall wart. I succeeded in getting things up and running with a Belkin F8T013 bluetooth dongle plugged in directly (I don't own a powered USB hub), paired with a TouchPad BT keyboard and all was dandy... until I gave it to Simon. ;)
I suspect this adds more weight to the argument for "get a good, name brand power supply rated 1A or better per port". HP I trust to produce a wall wart that puts out decent regulated power at the rated amperage. Some no-name chinese factory whose products are being bundled with "freebie" (and rather craptacular) android tablets? Less so.

The supply that's working (I couldn't be arsed to hack USB cables onto my 12A bench PSU in the end) is a Belkin 2.1A unit, intended for powering iPads.

Also, a very public thank you to Mark for sending me his Pi. A scholar and a gentleman of the first order. I don't normally "do" smileys, but...

Image

Simon

reggie
Posts: 151
Joined: Fri Aug 26, 2011 11:51 am

Re: voltage and polyfuse

Fri Jun 08, 2012 10:59 am

I think there has been a fair bit of discussion on the polyfuses already, at 3.5v across tp1/2 for the OP, that is clearly not good.

My fuses read:
F1 5.9ohms
F2 5.9ohms
F3 2.1ohms

There is a very minimal datasheet for the F1/F2 polyfuses, it doesn't make for particularly brilliant reading, the upshot is, if you're using your pi somewhere warm, expect the performance of the polyfuses to drop further.

There seems to be some confusion as to how much power the pi draws, officially, I thought it was supposed to be 1.1a via the microUSB, in reality, the F3 fuse is rated to 700ma, so effectively, 700ma or less depending on the quality of the polyfuse. For F1/2 the official rating is 100ma per port, with polyfuses rated to 140ma, it seems that the official 100ma is probably about right given the swing in performance with regard to ambient temperature.

I have noticed something else too, it's not just the power you need to look at, it's the cabling too. I bought a £7 extension with multiple heads, 2 or 3 times the thickness of a samsung charger cable that I've got, I measured the voltage across tp1/2 with the extension cable and microUSB head, then measured the voltage using the samsung cable. The extension cable was giving out 250mv less than the samsung one, that's a 250mv drop just because of the cable, nothing else plugged in except the hdmi and sd card.

I also measured with hub, keyboard, mouse in different combos on the board, the upshot was, simply plugging in my powered usb hub gives me another 250mv voltage drop on the 5v rail. mouse and keyboard in any combo gives me another 150ish mv drop across the 5v. So that's 650mv drop purely by plugging stuff in.

The first PSU I tried was an official apple iphone charger, rated 5v 1amp, it started out roughly at 4.89v with the 'good' cable in, so you can imagine what plugging in anything else did, with the voltage dropping to below the 4.75v spec for the 5v rail on the pi, amazingly, even at 4.2v everything still worked, I got errors with the SD and keyboard but the system still booted. I now have a better power supply, plugged into a 7ah 12v battery for the time being, needless to say, my 5v rail is now stable and in spec, all of my SD card and keyboard errors have gone.

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Fri Jun 08, 2012 11:11 pm

No boot 20 plus hours after last try resistance across the three polyfuses:
  • F3 1.4 (no change)
    F2 6.4
    F1 1.4
I'll leave it alone for 2 days this time.
While at it tested 5 power supplies, 2 blackberries (bb1 and 2) that had worked, a motorola that had worked, a samsung never tested and a no name that had worked. The blackberrys are hard wired 2 pair cable the later 3 are usb so I tested my motorola usb cable and a generic off the shelf cable. Differnce between cables was minimal at 10-20mV
  • bb1 5V 700mA 3.51V
    bb2 5V 700mA 3.53V
    motorola 5V 850mA 3.58V
    samsung 5V 1000mA 4.02V
    no name 5V 1000mA 4.01
Interestingly by the time I did a second reading on the no name, output had dropped to 3.78V and reistance across F3 had dropped to 1.1 ohm from 1.4.

I suppose I 'll just have to wait a little longer this time and hope for the best. I would expect that polyfuses were used as opposed to a replaceable fuse due to area and cost constraints but, since this one came from RS and I still have a backorder at Element 14 (3 minutes later on 29/02), it won't matter other than lost lunch money if I try to bypass the polyfuse which leads me to my original question.
<snipped> toss it or try to wire in a power supply to bypass the polyfuse if that is the problem.

Perhaps someone on the list can make a suggestion. Should I wire to each side of the polyfuse. Could I, for example, make up a little circuit with a regulator cap and replaceable fuse and connect there?

User avatar
bazza14
Posts: 66
Joined: Sun Jan 01, 2012 10:05 am

Re: voltage and polyfuse

Sat Jun 09, 2012 3:53 am

You're either incredibly unlucky with your power supplies or you have a problem. You seem to be drawing more current than normal. This would be a doddle to test if you had a bench psu that indicated V & I but we can do some math. Remember I don't know what you know so be patient with me. Unplug all usb devices from your Pi and power it up with your best psu. Check the 5V rail each side of F3 and make a note. Now power off the Pi and measure the resistance of F3 -- I = (Vhi-Vlo)/R. From the specs that should not exceed 500mA.
Now do it again with the key board and mouse attached, measure RF3 each time because it can change and this should be less 700mA. If these are good then it's safe enough to short out F3 and carry on testing. If you are still getting low voltages and you are using different supplies with different leads then either they are all rubbish or there is fault on the board and you can test for that by soldering wires onto F3 and R51 and hooking up a power supply that you can adjust. Just be careful not to let the smoke out.
BTW I've powered mine from a Huawei phone charger rated at 1A and got 4.85v at the test point.
LINUX convert since 2003

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Sat Jun 09, 2012 5:17 am

Thanks bazza14
As it was I had a good usb ps connected to a breadboard doing something else, It provides 4.94V. I'll use another usb cord same thickness but connectors both ends for this. Its rated at 5V 1000mA.

I had 263mA with nothing connected and 782mA with keyboard and mouse connected. Second reading brings no joy but perhaps I'll jump it anyway in a day or two. Its no good to me like this. Maybe set up something with an lm317.

The one thing that has me thinking its something othe than the ps/polyfuse is that the capacitor above FE1 and D17 get heat up to almost to hot to keep in contact with. I don't think that should be happening
Just be careful not to let the smoke out.
There have been times I could've hung eels over my bench :^)

User avatar
Grumpy Mike
Posts: 914
Joined: Sat Sep 10, 2011 7:49 pm
Location: Manchester (England England)
Contact: Website

Re: voltage and polyfuse

Sat Jun 09, 2012 10:42 am

justwantin wrote: I had 263mA with nothing connected and 782mA with keyboard and mouse connected.
.............
The one thing that has me thinking its something othe than the ps/polyfuse is that the capacitor above FE1 and D17 get heat up to almost to hot to keep in contact with. I don't think that should be happening
That implies that the keyboard and mouse are taking 519mA, if so you are trying to draw this current through two 140mA poly fuses. That is not going to happen.

Also if a capacitor heats up it means it is taking too much ripple current. This means your power supply is very faulty, either giving too much ripple voltage or even giving you AC. You need to look at the output with a scope or ditch the power supply altogether.

Helldesk
Posts: 13
Joined: Sat Mar 03, 2012 10:51 am

Re: voltage and polyfuse

Sat Jun 09, 2012 11:07 am

I am powering my Raspberry Pi through a powered hub that is powered by a 2.5 A wall wart. I don't know its quality exactly since I don't have an oscilloscope, but I could find out I guess.

Voltage output at the ports of the powered hub is 5.1 V. Measuring TP1 and TP2 of a running Raspberry Pi gives me 4.84 V. If I do 'sudo reboot' on the Pi, it shuts down and the voltage across TP1 and TP2 rises to 5.08 V and the Pi does not reboot. It will no longer boot at all until it has been unpowered for a few minutes. This non-booting behaviour has been happening from the beginning, before I was using the powered hub and powered it directly with the same wall wart. The only thing I have connected is a keyboard (on the powered hub), a composite lead for video and the the audio jack.

Sometimes when I just power cycle it without a nice shutdown, it boots up again right away, and sometimes it does not boot, requiring the wait of several minutes.

F1 6 Ohm
F2 5 Ohm
F3 1 Ohm (or less)

When powered up, the voltage across F3 seems to be about 0.1 V.

Edit: I just did some more tests and followed the TP1-TP2 voltage over several power cycling events, with NOTHING but composite video connected. Nothing was connected in the USB ports, not even a keyboard. I cut and reapplied the power maybe ten or a dozen times and almost half of those times the Pi did not boot, and the test point voltage rose to 5+ V. When it did boot, the voltage rose to the previously mentioned 4.84 V.

On the occasions it did not boot, I kept retrying and did not have to wait three minutes to succeed in booting up again. So... what makes a clean, by-the-numbers shutdown with a keyboard connected so fatal to the well-being of the Pi? I still don't have enough data to make or rule out a connection of any kind to the presence or lack of USB peripherals, but this was curious.

Helldesk
Posts: 13
Joined: Sat Mar 03, 2012 10:51 am

Re: voltage and polyfuse

Sat Jun 09, 2012 5:43 pm

I have now tested it with another, surely better quality general purpose power supply (capable of 5.2 A at 5 V) and it's the same deal. After a clean shutdown it does not boot up again, and the test point voltage rises up to the supply voltage. It's like the SoC simply does not wake up again, not until the Pi has been left untouched, without any power, for three minutes.

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Sat Jun 09, 2012 9:56 pm

I've tested again today and seem to be drawing ~14mA less with keyboard and mouse attached (led lit on mouse, keyboard has never lit up). I used same ps as yesterday as well as a blackberry which has worked previously and which is noted as good on the elinux wiki.
This means your power supply is very faulty, either giving too much ripple voltage or even giving you AC.
Which power supply? I have 5 here and all overheat the capacitor and/or diode below to one degree or another.

I think I'm going to put this in the fried basket and maybe try hot wiring some other time, In retrospect this trouble began after connecting the hdmi to a monitor after a boot. I only had one good boot after that. Maybe there was a power surge from the monitor to the pi that caused the present problem. Dunno

Thanks all for your interest. The next pi I'll treat very gently indeed. There's no lunch money left

User avatar
Grumpy Mike
Posts: 914
Joined: Sat Sep 10, 2011 7:49 pm
Location: Manchester (England England)
Contact: Website

Re: voltage and polyfuse

Sun Jun 10, 2012 2:11 am

justwantin wrote: Which power supply? I have 5 here and all overheat the capacitor and/or diode below to one degree or another.
In that case it would imply that the capacitor is screwed. Maybe it has been damaged by an over voltage at some time and now is very leaky. I would consider replacing it.
Diode overheating just implies too much current.

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Sun Jun 10, 2012 3:35 am

In that case it would imply that the capacitor is screwed. Maybe it has been damaged by an over voltage at some time and now is very leaky.
I sppose there is no way to test it short of taking it off the board.

User avatar
rew
Posts: 425
Joined: Fri Aug 26, 2011 3:25 pm

Re: voltage and polyfuse

Sun Jun 10, 2012 5:31 am

The 'pi will run without the big capacitor near the micro USB connector.
So even if it's broken the 'pi should work.

Measure the voltage between TP2 and both sides of F3. (TP2 is unmarked on the other side of the PCB, but you'll find it).
Check out our raspberry pi addons: https://www.bitwizard.nl/shop/

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Sun Jun 10, 2012 6:24 am

I removed the capacitor to test it. It seems to be OK AFAIK.Thinking this thing is probably fried and I missed the smoke I decided to connect two leads to the capacitors solder pads and try powering the pi from there. I usd a Motorola 5.1V 850mA phone charger that delivered 5.18 to a quick and dirty voltage regulator. I used a zener diode to get ~4.75 out and threw a 220uF cap in for the sake of good order.

I read 3.56 or so across TP1 & 2 and at F1 and F2

I don't know much about this stuff but it seems to me that having ruled out the capacitor as a problem and having bypassed F3 I should now have 4.something volts between TP1 and TP2 unless something else is eating my electricity.
Attachments
pi-ps.jpg
pi-ps.jpg (14.53 KiB) Viewed 11698 times

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Sun Jun 10, 2012 9:22 pm

Since my problem started I have noticed the cpu also gets hot to touch. I finally found the probe for my multimeter and took a reading of my CPU. Temperature leveled out at 60C. Of course there is no software running so does this high temperature indicate anything else?

User avatar
bazza14
Posts: 66
Joined: Sun Jan 01, 2012 10:05 am

Re: voltage and polyfuse

Mon Jun 11, 2012 12:32 am

500+mA for a mouse and keyboard !!!!!!! That's way too high. I don't get anywhere near that with wireless kb+mouse combo and wireless lan adaptor so that may have been your pi killer for I am convinced your pi is dead. When you get your new RPi I'd use a different kb & mouse.
I've mod'd my Pi to take the polyfuses out of the USB power. Here's a photo if you're interested.
http://www.raspberrypi.org/phpBB3/viewt ... 281#p96281
LINUX convert since 2003

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Mon Jun 11, 2012 12:53 am

I saw your bypass earlier when reading that thread. Did you take your ground off the diode? that's what it looks like. I understood you to say you did that to bypass F1 and F2 but that would still leave F3 between your ps and pi?

I'm really not sure if that 500mA is correct they are both MS and rated at 100mA each

Trouble started after connecting hdmi cable to monitor with pi running. I was using a dvi/hdmi adapter and my daughter's boyfriend said he thought he saw a spark jump between the female and male outer metal shells of the monitor and the adapter lug and socket.

User avatar
bazza14
Posts: 66
Joined: Sun Jan 01, 2012 10:05 am

Re: voltage and polyfuse

Mon Jun 11, 2012 5:07 am

justwantin wrote:I saw your bypass earlier when reading that thread. Did you take your ground off the diode? that's what it looks like. I understood you to say you did that to bypass F1 and F2 but that would still leave F3 between your ps and pi?

I'm really not sure if that 500mA is correct they are both MS and rated at 100mA each

Trouble started after connecting hdmi cable to monitor with pi running. I was using a dvi/hdmi adapter and my daughter's boyfriend said he thought he saw a spark jump between the female and male outer metal shells of the monitor and the adapter lug and socket.
The 500mA is from your figures
I had 263mA with nothing connected and 782mA with keyboard and mouse connected.
. Anyhow I think it's academic your pi certianly sounds like it's fried.
F3 is no longer in the cct as I've tapped off the supply side not the Pi side and ground from D17.
LINUX convert since 2003

User avatar
justwantin
Posts: 39
Joined: Thu Jun 07, 2012 8:40 pm

Re: voltage and polyfuse

Mon Jun 11, 2012 7:03 am

The 500mA is from your figures
500mA plus but it was so far out I was thinking perhaps I didn't measure/calculate correctly. I measured again later that day and had something equally odd, 82mA. Both keyboard and mouse are listed good on the wiki so who knows. There is nothing to the usbs now no matter how I power it, Cause could also have been a 4 port soniq powered hub as it did feed power into pi before I stopped using it. It also got warm and sniffing the usb ports smells like something wasn't happy in there. I seemed to have missed that listed on the wiki.

I'm ordering a belkin hub for next time round element 14 tells me my order will be filled later this month and hopefully I'm that much wiser :^)

User avatar
kerml
Posts: 83
Joined: Sun Aug 05, 2012 11:52 pm
Location: Portugal

Re: voltage and polyfuse

Sat Aug 18, 2012 2:10 pm

My rpi needs to be connect to the PS two times to boot!
On the first time only the power led lights up.
I disconnect immediately and connect it again and the pi boots. I don't have crashes or anything just this weird behavior.

The voltages drop on TP1-TP2 are variable because I tested a few PS.
The best I found is ZTE Blade smartphone charger (5V 700 mA)

It gives me 4.82V on TP1-TP2
My polyfuse F3 have a value of 0.6 ohm and a voltage drop of 0.13 when it boots!
I think that 0.6 ohm is too low and it could be damaged!
Any one can give me a second opinion?
Amor de Slackware
Portugal 2007

Return to “Troubleshooting”