Running with Power port unplugged


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by Lob0426 » Mon Aug 06, 2012 8:29 pm
danpeirce wrote:If I bought a hub that had this issue I would return it and get a different one. Others have pointed out that they have self powered hubs that do not do this. I'd suggest any work around is potentially more trouble that it is worth.


Thats just how twisted some of us are in this forum, :twisted: . I am trying to create this. :lol: ;)

There are several ways to work around it, alter the hub, alter the cable or alter the RasPi. These only work if you have the right skills to accomplish them. Its not hard, just kinda intimidating, to cut into any one of these solutions the first time. The easiest is to cut the red wire in the cable. Then the cable is only used to that hub. Sometimes returning the hub is just not an option and you already spent the money.

here are some pictures of a RasPi with no PSU working just fine! :D
No PSU.jpg
Look Ma no PSU, powered through USB port
No PSU.jpg (58.52 KiB) Viewed 1491 times

No PSU screenshot.jpg
Screenshot, yes it is all the way into LXDE!
No PSU screenshot.jpg (45 KiB) Viewed 1491 times

Currently the hub is not using Data over the same cable. It is only supplying power in the picture. But the power is going in through the USB port not an extra cable to the Micro USB. My hub will not back power in its stock condition. It will when I am finished modding it. I have already tested the Data cable that came with the hub and it is fully functional. The 500ma fuses I installed (F2 and F3) probably are not going to let this RasPi play Quake3. It will be a different story when the "A" model comes out. I could take the 700ma fuse that I removed (F3 new ones have 750ma) and place it at the USB (F2 bottom port) then the model B RasPi here would probably run everything. You could just remove F3 and replace F2 with it, without buying any components at all. By the Way my hub will output more than 500Ma from a single port. I do not know how much more. But it runs my USB HDD on a single port. It is running the Raspi! :P
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by Lob0426 » Mon Aug 06, 2012 10:07 pm
OK, modified the USB hub to see if could get power and data through the same cable. Was pretty sure I could but you have to try it first. In the following pictures you should note;
1.) No power cable in Micro USB port
2.) Only one cable in the RasPi's USB port. Keyboard and HDD plugged into Hub!
3.) Monitor picture shows 24GB Filesystem on open window. That is the HDD. Browsed the drive to make sure it was working.
hub powered.jpg
RasPi powered by hub through Data cable. No power Cable!
hub powered.jpg (52.35 KiB) Viewed 1483 times

Notice the little red wires that are twisted together? That is the jumper wires to power the Data port that was not connected. I will install a switch later so I can use it for other devices like the Panda Board. In this configuration there is no power being drawn except by the RasPi. So all 500ma belong to it. I really need an A model to take this where I want it to go.
screen shot HDD.jpg
Screenshot; File Manager showing HDD as 24GB Filesystem
screen shot HDD.jpg (39.04 KiB) Viewed 1483 times

A picture says a thousand words, but it would have been better if I could have had the RasPi and the Monitor in the same shot. Monitor sits atop my Windows Home Server and there was just no room to put the RasPi and hub up there. The 64K limit on attachments did not help either. :lol:
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by Lob0426 » Tue Aug 07, 2012 6:39 pm
An Update:
Ran my modded Raspi/hub for over ten hours last night, nothing real extensive, just updates upgrades and such. Let the screen saver go wild. Bounced around in LXDE. It ran perfectly the whole time. I did not try any heavy graphics. I was using the Ethernet quite a bit so there was a load on the LAN9512. All devices are attached to the hub including the keyboard/mouse wireles combo. it would be a great setup for headless operation. Considering installing the 700ma fuse that I took from F3 to F2. Then might try to run Quake3 to see if it goes down. Overall happy with the results so far. Dang it, I need an A model! :D
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by omiez » Sun Sep 30, 2012 10:52 pm
Hello Friends

I am about to recieve my Raspberry,ordered it yesterday and it will be the last revision without the Plyfuses.

I also ordered a power supply 5V 1.2A.
I want to connect a Powered USB Hub because i will use an external HDD 2,5".

My questoin is. Can i use the Power supply and the Powered USB Hub connected simultanesly or is it better to power the RPI through a Micro USB connected to the HUB without having problems with backpowering or similar?

If i Power from the Hub must i cut the +5V (Red Wire) from the usb Port connecting in USB port of the RPI?

Thank you.
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by wingsoflyra » Tue Oct 02, 2012 1:39 am
omiez wrote:Hello Friends

I am about to recieve my Raspberry,ordered it yesterday and it will be the last revision without the Plyfuses.

I also ordered a power supply 5V 1.2A.
I want to connect a Powered USB Hub because i will use an external HDD 2,5".

My questoin is. Can i use the Power supply and the Powered USB Hub connected simultanesly or is it better to power the RPI through a Micro USB connected to the HUB without having problems with backpowering or similar?

If i Power from the Hub must i cut the +5V (Red Wire) from the usb Port connecting in USB port of the RPI?

Thank you.


---

I had been running the pi off it's own separate PSU -and- also using a powered USB hub to run externals. On shutdown I had been unplugging the power cable to the powered hub first, then the pi's power cable to synch their power-off state together. Heck, I even plugged all the power supplies to a power strip and then hit the switch on the strip to get it to go down at the same time and avoid spiking the SD card. I just read in the Raspberry Pi User Guide today where Eben suggests
plugging the Pi's micro power connection directly into the powered USB hub. I think that works
the very best I've tried yet and I don't have to worry about any potential backfeed from the hub to the pi and smoking fuses. Just to be clear you don't want to run the pi just off the voltage from the hub without utilizing the pi's own power port. I've tried all these methods and I'm convinced Eben is dead on correct. It just flat out works better doing it the way he suggests.

So, I have eliminated the original PSU I had been using with the pi ( an HP 5v USB adapter at 2 amps) and it works very well to run the pi directly into the USB hub. The hub's transformer is also
2 amps and handles loads well. I have a Belkin WIFI dongle, the pi and a Logitech mouse dongle
all plugged into the USB hub. The best part is when I shutdown I just hit the switch on the power strip
and it goes down gracefully.
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by Lob0426 » Tue Oct 02, 2012 3:05 am
@wingsoflyra:
You should read this front page post from the new revisions of the PCB, posted by @Eben
http://www.raspberrypi.org/archives/1929

USB Output Power

The resetable fuses protecting the USB outputs have been removed. This feature was implemented on some later revision 1.0 PCBs by replacing the fuses with links; revision 2.0 permanently implements this modification. It is now possible to reliably power the RPI from a USB hub that back feeds power, but it is important that the chosen hub cannot supply more than 2.5A under fault conditions.

Back-powering is now a safe way to run your RasPi on a revision 2.0 PCB or earlier boards with the 0ohm resistors. I have been doing it on a modified Revision 1.0 board for a couple of months now, before the revisions.
My recommendations if you wish to try backpowering;
4 port hub with at least a 2A power supply.
7 port hub with at least a 3A power supply.
A short, 18" cable (.5 meter) or less.
I recommend a good quaility hub. Mine has been modified to take the power after the Hub polyfuse.
Either should work well on a board without polyfuses or has been modified to jumper the fuses. Expect TP1/TP/2 to be lower than when it is powered normally. the test points are now after all the regulators instead of before.
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by omiez » Tue Oct 02, 2012 3:51 am
It is a little confusing for someone that is noob in electrics. So i think that i probably will recieve the last revision with no polyfuses. So if i use a powered usb hub there is no need to connect the rpi's power connector to the power supply?
Is this right? Or must i connect a mini usb from the hub to the pi?


Make a drawing or picture to look how you connect please.
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by Lob0426 » Tue Oct 02, 2012 5:53 am
@omiez:
If you have a powered hub, that will supply power over the linkup port, you just need to plug it into the RasPi USB port and the hub. This is not how the hubs are supposed to be designed. The linkup port is not supposed to have power. But some hubs do supply power over the uplink port. Some people have modified their hubs to supply power over a single cable with a single power supply for the hub and RasPi. There are no drawings as every hub is different.

If you plug your RasPi into your hub, with no power supply attached to the RasPI power connector, and the red light comes on you may be able to power it through a SINGLE cable. If not, you can plug a micro B to USB A cable to a hub USB port then to the RasPi to power connector. There will be a second cable to the uplink port. That cable should have come with your hub.

Single USB cable: power and data over one cable. Back feeding through RasPi USB port.

Hub Power Supply -------- hub uplink port --------------USB Cable----------------- RasPi


Two USB cables: power over one cable data over the other. power still from hub.

Hub Power Supply ----- hub uplink port ----USB Cable -----RasPi
hub USB port ----USB Cable -- Raspi power connector

I recommend you use the two cable method until you have read enough in the forum to understand the power issues that can be present with your RasPi. Make sure your RasPi works with a standard power connection before you try anything else
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by omiez » Tue Oct 02, 2012 12:23 pm
Ok i think i am starting to understand it.

I connect the Uplink port to the USB port of the Pi and will use one USB port from the HUB to the Pi's Power Connector.

I ordered also this Hub have a look at it.
http://www.vesalia.de/d_usb7porthub.htm

It has 7 ports and 5V 3,5A Power Adapter. This must be enough to power the hole system using Keyboard,Mouse,Wireless and USB HDD.
I'll try to setup the system to use with VNC so to disconnect Keyboard and Mouse.

I am waiting a confirming email from Vesalia that they sent me the rasp cause the day after my order the Pi was sold out.

Thanks for your help!
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by Teekert » Thu Jan 03, 2013 8:35 pm
Ok, one last question.

I apparently own a hub that also provides power to the port that should just pas data to the hub front ports. I was quite surprised that my Pi booted upon connecting it.

My question:
Does this hurt?
I understand that the power supply may be undefined this way so I will also connect the microusb port for power but will I damage my Pi or create a dangerous situation when providing power the usual way + the strange way? Should I return the hub? It says it is FCC approved on the back...

Thank you all.
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by Teekert » Thu Jan 03, 2013 8:39 pm
Ok after now reading the whole thread I understand that I should not use my usb hub!

It would be nice to add warnings to the Pi package... I have 2 useless sd cards now (didn't think there would be problems and found many afterwards) and 2 useless usb hubs.

Well I guess that is what you get as an early adapter...
Might try to kill the power in the cable then, as a last resort.
Thanx for all the info.
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by Teekert » Thu Jan 03, 2013 8:58 pm
Ah, as posted before here it says:
http://www.raspberrypi.org/archives/1929

That on a later revision you can back power the board (I know, was mentioned, just giving the source.)

I did notice the case becoming a bit warm but I don't know if that is normal. Will test when I'm not asleep (I blew up an iPhone charger from dealextreme last week using the Pi, it was all black inside) Good night!
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by Lob0426 » Fri Jan 04, 2013 3:21 am
If you have a version that does NOT have USB polyfuses, it will back-power just fine. You should not connect a power supply and a hub the "back-powers". You can either run it with just the hub power, if the hub has a decent power supply or just the micro-usb power, or modify your hubs cable to not supply power and power weach seperately!
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by Teekert » Fri Jan 04, 2013 8:03 am
That is not nice, it means I will have an unreliable power supply (I assume the backport of my hub is not well defined and there is just leaking current).

I think it is a bad decision to make this possible it limits you to certain hubs, I don't suppose I can email my supplier and ask him which hub he has that does not leak current from the back of the hub...

I do need to use the hub because the usb port on the front of the Pi gives to little power for my wireless keyboard (I have to sit very close to the receiver)
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by Teekert » Fri Jan 04, 2013 8:38 am
Ok, I'll just get my tweaking juices flowing and start by blocking the outermost connections on the USB cable that goes into the front op the Pi (the double port, not the power supply port) and the back of the Hub :) (1 and 4 in this image:)

http://en.wikipedia.org/wiki/File:USB.svg

I will report back.

BTW even cooler would be to break the power connections to the back port inside the Hub, lets see....
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by Teekert » Fri Jan 11, 2013 7:58 am
Reporting back: Pi has been running for days powered via the front usb port, it hardly gets warm and is stable.
I'll keep it like this :)
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by Lob0426 » Fri Jan 11, 2013 5:21 pm
I have a modified ver1.0 that has been running just fine, since August 2012. It is powered from a modified hub. The hub would not provide back-power.

viewtopic.php?f=41&t=16473

The first one gave me a lot of problems with low voltage at the Test points. I eventually hardwired the hub to the RaspBerry Pi. The second one I just made up a couple of days ago is doing ok at 4.92V. Modified the same kind of hub and shortened a USB cable down. It is not hardwired. This RasPi is a ver2.0 512MB so I did not have to modify the actual RasPi. The cable is still longer than I want it to be.

Note: this second RasPi has a really low drop through F3. It can run a USB HDD directly from the bottom USB port without a hub. My other 512MB will not do this. I will probably switch the two. The other one is on my Lapdock.

I will get some pictures of the new hub powered RasPi into that thread in the next couple of days.
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by pluggy » Fri Jan 11, 2013 6:49 pm
With a Rev 2 Pi, I'd say the recommended way of running it is back powering it from a powered hub. I get a whole 5V across the test points. None of my Pis do better than 4.85 the traditional way through the polyfuse.
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by Lob0426 » Sat Jan 12, 2013 2:22 am
pluggy wrote:With a Rev 2 Pi, I'd say the recommended way of running it is back powering it from a powered hub. I get a whole 5V across the test points. None of my Pis do better than 4.85 the traditional way through the polyfuse.


I get 4.98V with an Adafruit Power Supply and a 10" A to micro B USB cable. Of course that power supply is supposed to be putting out 5.25V. Using short USB cables always gives better results. I need to see what the resistance F3 on that board is. I have a 1.1A polyfuse I could replace it with, but why bother if it is back-powered!

There is loss through the USB connectors themselves. The rev1.0 was even worse and that is why I decided to hardwire it. It also showed large drops (and resets) when hotplugging. Now it has none of those problems. The rev 2.0 was just easier to do. Did not have to modify the RasPi, just the uplink on the hub. The Loss though the connectors on this rev2.0 is less than the earlier RasPi. The rev1.0, I was putting 4.98V in and was only seeing 4.3V at the test points. After I hardwired it I have 4.92V. I would probably see even higher if I had taken the power before the polyfuse in the hub rather than after it. My new setup has about a 5" USB (A to miniB) cable now. It may end up with a pin header and connector, have not decided yet.
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