Power supply WARNING


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by plugwash » Sun Jan 08, 2012 3:52 am
Not so long ago someone warned that it was a bad idea to get your SD cards from ebay. However at least with SD cards the worse that is likely to happen is a corrupt OS install. I'm posting this to inform you that SD cards are not the only thing you shouldn't be buying on ebay.

The following post recently came up on a mailing list I subscribe to titled ""

http://www.piclist.com/techref.....8;tgt=post

The USB PSUs in question apparently had no regulation at all and if run on a 240V supply could output nearly 10V.

What will happen to a pi if something puts nearly 10V on the 5V line? My guess is it's very likely to fry some components (what exactly is powered off the 5V line directly anyway?).
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by jwatte » Sun Jan 08, 2012 8:11 am
There is actually power protection circuitry on the 5V input rail. And not much run on that, anyway -- the main CPU runs on 3.3V, which is regulated down from 5V. You *may* end up feeding the 10V out to any other USB device, though.

There were some power schematics posted on the forums a while back -- you could probably find them using the search function in the forum header.
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by Jongoleur » Sun Jan 08, 2012 9:25 am
@plugwash:

Just watched the teardown of a USB psu from your link.



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by plugwash » Sun Jan 08, 2012 9:57 am
jwatte said:


There were some power schematics posted on the forums a while back -- you could probably find them using the search function in the forum header.


Presumablly you mean

http://www.raspberrypi.org/wp-.....12/psu.png

From the schematics it looks like there is overcurrent protection followed by some kind of voltage clamp diode. No idea if it's fast enough and robust enough to save the board from a 10V power supply.

Unfortunately that png doesn't show what is powered off each rail. They don't even show where the 1V2 regulator inside the SOC gets it's power from.
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by bf4ed » Sun Jan 08, 2012 10:18 am
Just add LM7805 before power input of r-pi. For use in car or home its wise to add some voltage stabilizer, just bo be on the safe side. Then you can use a cheap ebay supply.
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by gregsie » Sun Jan 08, 2012 11:10 am
I'm going to use a genuine HTC  mains charger. it is rated 1A, is small light and looks cool.

If you're going to use a 7805 with a 12V supply you'll probably need a heatsking as it could dissipate 7W at full load. not good.
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by Prometheus » Sun Jan 08, 2012 11:12 am
plugwash said:


Not so long ago someone warned that it was a bad idea to get your SD cards from ebay. However at least with SD cards the worse that is likely to happen is a corrupt OS install. I'm posting this to inform you that SD cards are not the only thing you shouldn't be buying on ebay.

The following post recently came up on a mailing list I subscribe to titled ""

http://www.piclist.com/techref.....8;tgt=post

The USB PSUs in question apparently had no regulation at all and if run on a 240V supply could output nearly 10V.

What will happen to a pi if something puts nearly 10V on the 5V line? My guess is it's very likely to fry some components (what exactly is powered off the 5V line directly anyway?).


That was me who posted the SD Card warning. :P

Anyway, brilliant post, this! Do you mind if I add it to my signature along with the SD Card warning?

bf4ed said:


Just add LM7805 before power input of r-pi. For use in car or home its wise to add some voltage stabilizer, just bo be on the safe side. Then you can use a cheap ebay supply.


I'm not sure why anyone would want to risk using one of these or one of these, myself. Never mind the risk to the Raspberry Pi - what about the risk to life and limb? (The BBC covered a particularly tragic story relating to exactly that in the programme "Fake Britain" in 2010, on that note.)
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by hippy » Sun Jan 08, 2012 1:09 pm
bf4ed said:


Just add LM7805 before power input of r-pi. For use in car or home its wise to add some voltage stabilizer, just bo be on the safe side. Then you can use a cheap ebay supply.



The problem is that people buying a supply marked 5V and suitable for USB powering will expect it to be a 5V supply with tight regulation to that. They won't know they have to use an additional regulator until possibly too late. Outputting 12V isn't the worse of it; get something really bad and you can find it puts mains out!

These issues have been discussed before on the forum with the only practical suggestion being to buy quality supplies from reputable dealers and be prepared for the consequences of things not always being what they seem or as advertised when trying to save money or cut corners.

I believe the foundation is planning to offer its own PSU so, if concerned, simply buy that; it will have been tried and tested and you will know what you are buying will work and not damage anything. If anyone chooses to do otherwise they have to accept all the risks in doing that.
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by grumpyoldgit » Sun Jan 08, 2012 1:19 pm
Being non-technical, if a psu is being offered as an extra, I will be more than happy to go for that.
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by alexandru.cucu » Sun Jan 08, 2012 1:53 pm
I have seen so many USB power supply units outputting more than 5 volts that I have lost my hope in finding a good one.

Most of them are even labelled with 5.7 volts.
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by hajj_3 » Sun Jan 08, 2012 2:19 pm
i was unaware of these problems with psu's! I bought a uk plug with a usb port on it for 99p delivered from china a few months ago, starting to think it could be pretty dangerous.
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by sorvad » Sun Jan 08, 2012 2:40 pm
I bought a USB powered hub which should be the right voltage etc. as it's being used as USB but as it was fairly cheap I wonder about it's quality :-/
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by hippy » Sun Jan 08, 2012 2:42 pm
hajj_3 said:


i was unaware of these problems with psu's! I bought a uk plug with a usb port on it for 99p delivered from china a few months ago, starting to think it could be pretty dangerous.


You have three choices -

1) Use it and keep your fingers crossed

2) Don't risk it and throw it away or don't use it

3) Minimise the risk – plug it into an RCD or similar safety cut-out mains socket, wear eye protection and turn it on at arms length not connected to any device. If you have the experience, check the output voltage with a multimeter.

I don't plug any mains adapters or equipment in without using a mains safety cut-out first time and always measure adapter voltages if it did not come as the recommended manufacturer's supply with a product.

There may be longer term issues which aren't observed immediately, such as overheating with use, so don't just plug in and leave on over night, check if it gets hot during the day when you can keep an eye on things first.

There's no guarantees there won't be problems unless manufacturer supplied or recommended and you have to rely on gut feeling and make the gamble one way or the other.

I wouldn't use any adapter if I couldn't check the voltage it puts out. That may just be me being overly pessimistic but I've had adapters which would have damaged things if I'd believed how they were marked and hadn't known that.
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by roelfrenkema » Sun Jan 08, 2012 2:49 pm
Considering the target group it would be nice if there could be some real documentation on this issue instead of the endless speculations here. I presume a good quality hub or adapter (meaning no obvious cut on the price crap) will be just fine. If not Raspberry would be in deep trouble considering some legal issues in most european countries where warrenty is a legal right.
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by grumpyoldgit » Sun Jan 08, 2012 3:06 pm
This is all quite worrying. I had always taken the view that Ebay type stuff was O.K. and that it was just the retailers making excess profits. I will now need to take a closer look at some of the stuff I have bought over the years, and will be much more wary in future about what and where I buy.
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by abishur » Sun Jan 08, 2012 3:11 pm
The good news is that, as was previously mentioned, there is voltage protection on the board and it was designed with this very scenario in mind.

Also, the USB would not receive too high a voltage as it is behind the voltage protection, so no worries there either ;-) That said, however, you can bypass the voltage protection by using the two GPIO pins that have been repurposed to the 5V rail (5v source/sink pins), any power drawn *from* the pins are behind the voltage protection, but any power sent *into* the pins do not go through the board's voltage protection, so you will have to make sure to add the appropriate protection yourself!

And, as one more bonus, the r-pi foundation has stated that they already plan on selling an appropriately powered PSU so you can grab one from them and be confident of it's ability to power your board :-)
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by hippy » Sun Jan 08, 2012 3:26 pm
Abishur said:


The good news is that, as was previously mentioned, there is voltage protection on the board and it was designed with this very scenario in mind.

Also, the USB would not receive too high a voltage as it is behind the voltage protection, so no worries there either ;-)

And, as one more bonus, the r-pi foundation has stated that they already plan on selling an appropriately powered PSU so you can grab one from them and be confident of it's ability to power your board :-)


I'm not sure how the voltage protection would stand up to very high voltages or even mains in the worst case and wouldn't like to find out! The danger from such a situation would be more than just electrical damage.

My recommendation would be to buy an official R-Pi PSU from the foundation, then there are no worries, and for that alone it will be money well spent.
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by Prometheus » Sun Jan 08, 2012 3:33 pm
Grumpyoldgit said:


This is all quite worrying. I had always taken the view that Ebay type stuff was O.K. and that it was just the retailers making excess profits. I will now need to take a closer look at some of the stuff I have bought over the years, and will be much more wary in future about what and where I buy.


That's a pretty common point of view, but sadly one that can lead people to getting scammed (see the SD Card thing in my signature), injured, or killed… :/

Still, good to know that you'll be more wary – that can only be a good thing. :)

hippy said:

My recommendation would be to buy an official R-Pi PSU from the foundation, then there are no worries, and for that alone it will be money well spent.

That's what I'll be doing. Seems like much less hassle, to me. (I don't have any micro-USB power supplies lying around, myself!)
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by hippy » Sun Jan 08, 2012 3:42 pm
And just in case anyone thinks the risk of mains being put on the "5V" side of an adapter is being exaggerated, it's worth checking out product recall information such as this ...

http://www.energetix.recceolog.....;Itemid=49

There are a number of recalls there for adapters and chargers which through poor design could put mains out, causing damage and being life threatening. Thankfully most potential failures don't materialise, but there is real risk.
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by PiOfCube » Sun Jan 08, 2012 3:46 pm
Take a look on sites like Amazon also, you will find many customer reviews that have the same theme… "The adapter plug fell apart when I pulled it out", "A bad smell came out of the plug and then it started to smoke", "The listing said this was adapter was made by xyz but the one I got didn't have a manufacturer". Most (if not all) of these were comments regarding marketplace sellers.

If I am buying power supplies (usually anything that plugs into the mains) from Amazon, I always look for items sold directly from Amazon themselves. This does not completely prevent "fake" goods being sent but it does limit it by a considerable factor.

Anyone remember the scandal a few years back when airline companies were found to be using fake parts (quite often stuff made from compressed cardboard instead of high-tec composites)?
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by Prometheus » Sun Jan 08, 2012 3:56 pm
hippy said:


And just in case anyone thinks the risk of mains being put on the "5V" side of an adapter is being exaggerated, it's worth checking out product recall information such as this ...

http://www.energetix.recceolog.....;Itemid=49

There are a number of recalls there for adapters and chargers which through poor design could put mains out, causing damage and being life threatening. Thankfully most potential failures don't materialise, but there is real risk.



And that's for legitimate products. You don't get recalls for poorly-designed, poorly-manufactured fakes...
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by hippy » Sun Jan 08, 2012 4:01 pm
A worrying assessment of 'cheap import' chargers which is well worth the read ...

http://www.esc.org.uk/industry.....g/chargers

Buying cheap may turn out to be false economy or even worse.
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by stormy1 » Sun Jan 08, 2012 4:06 pm
The Kaito PST-15U is a rock solid 5v 2A usb supply for those in the US in my experience.

I have used dozens of them in various ways.

All have been spot on at 5v
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by stormy1 » Sun Jan 08, 2012 4:22 pm
Here is a link to information on the oem in case someone is interested in talking to them about a UK version and or bulk orders:

http://spikecn.en.made-in-chin.....ation.html
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by emilio » Sun Jan 08, 2012 5:04 pm
Can I use a mobile phone charger?
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