Raspberry Pi Forums

Posted: **Mon Apr 08, 2013 1:32 pm**

Hi there,

Im new here and new to RPi etc., but have set mine up with xbmc and OPENelec no problems. However, I would really appreciate some help with the following:

I plugged my external portable Western Digitial 1TB HDD into the USB of the RPi and its works fine. The HDD does not have its own power supply. I am worried though that it might be damaging the RPi as it may be getting too hot or drawing too much power. I have read that powered USB hubs should be used to get external HDD's to work. However mine is already working, so do I need an external USB hub to stop it damaging the RPi, or catching on fire on something? Or am I good to carry on as I am. I want to leave the RPI and HDD turned on all the time and at the moment the above is concerning me somewhat.

I did have an issue before when my wireless mouse was plugged into the other USB port at the same time as the HDD and it was causing the RPi to reboot. I dont use the mouse now anyway so the RPi only has an HDMI cable connected and the external HDD. Its working fine again now only the USB HDD and HDMI is connected, but the mouse must have 'tipped it over the edge'.

I dont like to ank questions that have already been asked a million times, but I dont seem to be able to find an answer to the "is it ok to have an external HDD connected directly to the RPI, if it all works, in terms of power, heat and house-fires

". Do I need a USB hub regardless?

I did see the following on this forum:

"by mahjongg » Sun Feb 24, 2013 3:05 am
the PI has a polyfuse rated at about 1.1A, for everything! As the PI itself can use about 400 to 500 mA (depending on what it is doing), and you want to be well below the tripping point of the polyfuse, this leaves only a few hundred milliamps for the USB port, not enough for something as power hungry as an USB hard-disk."

So I assume that my HDD is not very hungry and must be using around 500mA as it still works, but am I "well below the tripping point of the polyfuse"?? It all works whether the hard-disk is spinning or not.

I watched a film via it last night and left it switched on overnight and its been on all day, and hasn't rebooted ot anything

Am I worrying about nothing, or will it overheat and wear the harddrive or RPi prematurely?

Any advice would be really appreciated!

Thanks in advance.

Kam

Posted: **Mon Apr 08, 2013 4:17 pm**

Unlikely you'll cause serious damage. What normally happens that the Pi will not boot or devices become unreliable (up to the point where data can get corrupted).

I *would* make sure that everything is indeed working properly. I have had a situation where even with a powered hub the external HD would disconnect / connect every couple of minutes.
You can check this with 'dmesg'

Gr.
Dirk.

Posted: **Mon Apr 08, 2013 6:55 pm**

Only version 1.0 boards have the poly fuses. All 512mb models do not have polyfuses. Your RasPi may be running that HDD just fine.

If you need to use other devices with it you will probably have to dig up a powered USB hub. Choose a hub with at least a 2A power supply if you need one.

If it is running with the HDD then it should be ok.

Posted: **Mon Apr 08, 2013 7:24 pm**

DirkS wrote:Unlikely you'll cause serious damage. What normally happens that the Pi will not boot or devices become unreliable (up to the point where data can get corrupted).

I *would* make sure that everything is indeed working properly. I have had a situation where even with a powered hub the external HD would disconnect / connect every couple of minutes.
You can check this with 'dmesg'

Gr.
Dirk.

Thanks for this! I have run the dmesg command but Im not sure what it means to be honest. What are the numbers down the left hand side? If my HDD was rebooting what would it show?

How would I know if the HDD was rebooting or becoming unstable?

Regards
Kam

Posted: **Mon Apr 08, 2013 10:00 pm**

Numbers on the left is seconds since start of boot, so the last msg was logged after about 90 seconds.
The message is about mmc0, which I think is the SD card device. They seem to be just ordinary warnings, nothing to worry too much about.

Problems with the HD would most likely be about sda or sda1.

Gr.
Dirk.

Posted: **Mon Apr 08, 2013 10:05 pm**

DirkS wrote:Numbers on the left is seconds since start of boot, so the last msg was logged after about 90 seconds.
The message is about mmc0, which I think is the SD card device. They seem to be just ordinary warnings, nothing to worry too much about.

Problems with the HD would most likely be about sda or sda1.

Gr.
Dirk.

ok, great stuff. Thanks a lot!

Kam

Posted: **Tue Apr 09, 2013 2:15 pm**

Lob0426 wrote:Only version 1.0 boards have the poly fuses. All 512mb models do not have polyfuses. Your RasPi may be running that HDD just fine.

If you need to use other devices with it you will probably have to dig up a powered USB hub. Choose a hub with at least a 2A power supply if you need one.

If it is running with the HDD then it should be ok.

Ok, thanks for your help. I'll source a powered hub if I come across any problems, although so far so good.

Posted: **Tue Apr 09, 2013 3:30 pm**

Lob0426 wrote:Only version 1.0 boards have the poly fuses. All 512mb models do not have polyfuses. .

Err, no! you are talking about the low current USB OUTPUT fuses, I was talking about the 1,1A INPUT fuse which ALL PI's have!

Posted: **Tue Apr 09, 2013 3:43 pm**

mahjongg wrote:
Lob0426 wrote:Only version 1.0 boards have the poly fuses. All 512mb models do not have polyfuses. .
Err, no! you are talking about the low current USB OUTPUT fuses, I was talking about the 1,1A INPUT fuse which ALL PI's have!

Do you agree that if the HDD is working directly into the Pi then I dont need a powered USB hub? As mentioned in my original post Im concerned about heat and either damaging the Pi or HDD, as Ive read the USB ports are only really designed for mice and keyboards etc. Is it a case of 'its working so leave it' or get a USB hub?

Other responses seem to suggest its fine, but the the bit about fuses confuses me as I dont know anything about it.

Thanks in advance.

kam

Posted: **Tue Apr 09, 2013 3:52 pm**

The jury isn't out yet, some people claim that it works, and continues to work, but it all depends on how much current in total is ran through the polyfuse, and a mass of other parameter, among things such as the ambient temperature of the PI, and if the polyfuse happens to be one that triggers later rather than sooner (production differences) . What could happen is that the polyfuse "blows", and then everything stops working! If you then remove the HD, and wait 24Hours for the polyfuse to "cool off" (regenerate actually) then your PI probably starts working again, but if you try running it with HD again, then the polyfuse will probably blow far sooner than before etc etc.

If you think you are handy in replacing the polyfuse (or perhaps easier soldering a new one on top) then you might consider the risk to be low.

By the way, you don't necessarily need a hub, what you need is to power the HD without the power (current) going through the PI's polyfuse.

What I would do, (but I'm an experienced electronic engineer) is to find a point on the PCB before the polyfuse, then find the 5V pin of the (top) USB connector, (bottom 5V pin is far less accessible) cut that pin loose from running to the PCB, and then solder a wire between the point before the polyfuse to the 5V pin of the USB connector, so that only the 5V to the top USB port bypasses the polyfuse.

Posted: **Tue Apr 09, 2013 4:00 pm**

mahjongg wrote:The jury isn't out yet, some people claim that it works, and continues to work, but it all depends on how much current in total is ran through the polyfuse, and a mass of other parameter, among things such as the ambient temperature of the PI, and if the polyfuse happens to be one that triggers later rather than sooner (production differences) . What could happen is that the polyfuse "blows", and then everything stops working! If you then remove the HD, and wait 24Hours for the polyfuse to "cool off" (regenerate actually) then your PI probably starts working again, but if you try running it with HD again, then the polyfuse will probably blow far sooner than before etc etc.

If you think you are handy in replacing the polyfuse (or perhaps easier soldering a new one on top) then you might consider the risk to be low.

Thats seems to make sense. I certainly wont be soldering anything.... so USB hub it is then!

I appreciate your assistance

Kam

Posted: **Tue Apr 09, 2013 4:09 pm**

mahjongg wrote:The jury isn't out yet, some people claim that it works, and continues to work, but it all depends on how much current in total is ran through the polyfuse, and a mass of other parameter, among things such as the ambient temperature of the PI, and if the polyfuse happens to be one that triggers later rather than sooner (production differences) . What could happen is that the polyfuse "blows", and then everything stops working! If you then remove the HD, and wait 24Hours for the polyfuse to "cool off" (regenerate actually) then your PI probably starts working again, but if you try running it with HD again, then the polyfuse will probably blow far sooner than before etc etc.

If you think you are handy in replacing the polyfuse (or perhaps easier soldering a new one on top) then you might consider the risk to be low.

By the way, you don't necessarily need a hub, what you need is to power the HD without the power (current) going through the PI's polyfuse.

What I would do, (but I'm an experienced electronic engineer) is to find a point on the PCB before the polyfuse, then find the 5V pin of the (top) USB connector, (bottom 5V pin is far less accessible) cut that pin loose from running to the PCB, and then solder a wire between the point before the polyfuse to the 5V pin of the USB connector, so that only the 5V to the top USB port bypasses the polyfuse.

That is way beyond me in terms of soldering. Im more likely to wreck it altogether than make it better. My Pi is powered by a plug and PSU. If I bought a powered USB and ran the Pi's power from the hub via the USB port rather than via the plug socket and PSU, would that be ok? Or maybe have the USB hub plugged in and still use the power cable that I use at the moment for the Pi?

Posted: **Tue Apr 09, 2013 4:20 pm**

You are talking about what is commonly know here as "back feeding the PI", which will work well (with revision 2 PI's), but has a distinct disadvantage that you bypass the PI's polyfuse altogether!
That means that if there is ever a short in the PI (or any of the 5V devices connected to the PI, including the HDMI) then the polyfuse isn't there to limit the current. Also the PI has an over-voltage protection device (TVS diode) that will short the 5V if it ever rises as high as 6V. For example when plugging in a PSU that, when it has no load, outputs a greater than 6V signal.

There are stories here about people that have holes molten in their enclosure because the TVS device became extremely hot.

Posted: **Tue Apr 09, 2013 4:37 pm**

mahjongg wrote:You are talking about what is commonly know here as "back feeding the PI", which will work well (with revision 2 PI's), but has a distinct disadvantage that you bypass the PI's polyfuse altogether!
That means that if there is ever a short in the PI (or any of the 5V devices connected to the PI, including the HDMI) then the polyfuse isn't there to limit the current. Also the PI has an over-voltage protection device (TVS diode) that will short the 5V if it ever rises as high as 6V. For example when plugging in a PSU that, when it has no load, outputs a greater than 6V signal.

There are stories here about people that have holes molten in their enclosure because the TVS device became extremely hot.

So whats do you suggest. Back feed the Pi, get a USB hub and power the Pi via the micro USB as I do now....or just leave it as it is which is Micro USB for power, HDD plugged in, without a USB hub?

Thanks
Kam

Posted: **Tue Apr 09, 2013 10:54 pm**

I wouldn't trust powering the HD directly through the PI, without modification (actually I myself would do it, because for me its easy to replace the polyfuse if it blows, but its not something I am prepared to advice for most)
Try to find a hub that doesn't back feed (use the wiki to find one). Its the very cheap ones that do, so they can also be used/sold as bus powered devices without a PSU.
If the hub backfeeds then try to use one that has a fused input, or use a fused PSU for it
If it backfeeds there is no sense in also feeding it the proper way through the micro-USB, as all the current will run through the back feed and none through the front.
If you use a hub that backfeeds be aware that the PI is unprotected, don't use it prolonged times unobserved!

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