Polyfuse F3 / RasPi power circuitry flawed


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by rurwin » Fri Dec 21, 2012 1:52 am
Why are barrel-connector PSUs considered better than Micro-USB? They have no standard to adhere to, so nothing to hold them to regulating current and voltage. Sure the expensive ones will be good, but the cheap ones will be just as bad or worse than the micro-USB ones. Then there is the confusion around the huge number of different sizes and polarities of the connector. If the RaspPi had an input of 6-24V with a full-wave rectifier and switch-mode regulator, maybe a barrel-connector PSU could be used, but that would add a fiver to the cost of the board and still need a dedicated PSU with the right-size connector to be bought. Far better to use that £5 to bundle a micro-USB PSU for those that need it.
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by tufty » Fri Dec 21, 2012 6:36 am
mahjongg wrote:you are talking about chinese junk chargers that happen to use a molded on micro USB connector cable.

mahjongg wrote:I'm not dismissive

No? You're certainly coming across that way, and if you'd bothered to read the rest of my previous comment you'd have realised that I'm *not* talking about cheap junk chinese chargers[1].
mahjongg wrote:Power supplies are OK chargers, but chargers are rubbish power supplies, so hopefully chargers will disappear from the market, or at a minimum will be more easy identifiable as such.

Totally agree. However, at the moment, they are *not* easily identifiable, and "power supplies" are the minority on the market

Simon

[1] Although someone did mention chinese chargers earlier.

mahjongg wrote:EU and Chinese standard supplies/chargers, that will give out a steady 5V.
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by rurwin » Fri Dec 21, 2012 7:36 am
I will have to get my finger out and build that power supply tester I bought all the bits for six months ago. Maybe over Christmas...

...If I used relays instead of switches, I could control it from a RaspPi and do transient measurements and stuff...

...but then I'd need a power supply for the RaspPi.
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by jamesh » Fri Dec 21, 2012 8:59 am
The problem of charger just being crap is not limited to uUSB - any charger that is crap, is crap, no matter what the connector! So if we had put on a barrel connector we would, in all likelihood, still be getting threads like this, because the charger is still crap!

As to devices that use it - I have a Nokia phone - uUSB, a Amazon Kindle, uUSB, A Kindle Fire, uUSB, , some proto phones from A.N.Other manufacturer, uUSB. The other day I couldn't find an old micro cable! It's the way the world is going. And I'm not even that much of a gadget person!
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by mahjongg » Fri Dec 21, 2012 11:48 am
There are cheap Chinese junk products out there, and currently it can be difficult to distinguish them from better products, but what I'm trying to point out is that both the Europeans and the Chinese are trying to improve the situation by defining new rules for a standard charger/power supply, one that has 5V regulated output within 5%. When these chargers replace whats currently in the market the current situation will much improve. Also, because these chargers should be identifiable as such.

See: http://www.eetimes.com/design/communications-design/4016269/How-to-conform-to-China-s-new-mobile-phone-interface-standards?pageNumber=0

Quote from the article:
The output voltage characteristic is defined by the new regulation. The nominal output voltage of the charger should be 5 V with a +/-5% tolerance; that means, the input voltage to the mobile phone connector should remain between 4.75 V to 5.25 V.
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by Gerry-VE4GKS » Sat Dec 22, 2012 12:10 am
mahjongg wrote:
doveman wrote:Whilst it may well be technically superior, it's also rather impractical for DIY use due to the size making it impossible to solder a microUSB plug to a lead and the fact that it is only meant to carry 5v.

So it might have been nice if I could have fitted a microUSB socket to my case instead of a barrel connector but aside from the impossibility of soldering the socket to the rest of the circuit and swapping the barrel connector on the PSU for a microUSB plug, I also needed to input 12v into the UBEC, not 5v and obviously I can't (even if I physically were able to) fit a microUSB plug to a 12v PSU, as then it could be plugged into some other microUSB socket, blowing whatever was designed to only take 5v.

None of which is to say that it was the wrong decision to use microUSB on the Pi, just that if the barrel connector is so bad it would be nice if someone would come up with something better that can be used for DIY projects as well.

Yes, micro USB connectors are not meant for hobby projects, but note that you can wire up any other connector to the PI through the use of the 5V and GND pins on the GPIO header, only do note that in that case you are bypassing the polyfuse, which also makes the 5.6V over voltage protection inefficient. So you can still wire a up 5V to your PI without using the micro USB port, if you are desperate to do so.
There are AFAIK no power plugs that enforce the use of 12V, except if you count the cigar plug as such, but that one is a bit too bulky to be practical.
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by Dilligaf » Sat Dec 22, 2012 12:40 am
mahjongg wrote:There are cheap Chinese junk products out there, and currently it can be difficult to distinguish them from better products, but what I'm trying to point out is that both the Europeans and the Chinese are trying to improve the situation by defining new rules for a standard charger/power supply, one that has 5V regulated output within 5%. When these chargers replace whats currently in the market the current situation will much improve. Also, because these chargers should be identifiable as such.

See: http://www.eetimes.com/design/communications-design/4016269/How-to-conform-to-China-s-new-mobile-phone-interface-standards?pageNumber=0

Quote from the article:
The output voltage characteristic is defined by the new regulation. The nominal output voltage of the charger should be 5 V with a +/-5% tolerance; that means, the input voltage to the mobile phone connector should remain between 4.75 V to 5.25 V.


You see, that's the problem a charger/supply that puts out 4.75-4.8 volts is in spec but by the time it gets to the guts of the PI it's under spec. The standard should be 5.0 to 5.25 or even 5.5 to make up for volt drops in cables etc.
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by mahjongg » Sat Dec 22, 2012 2:01 am
Dilligaf wrote:You see, that's the problem a charger/supply that puts out 4.75-4.8 volts is in spec but by the time it gets to the guts of the PI it's under spec. The standard should be 5.0 to 5.25 or even 5.5 to make up for volt drops in cables etc.

The standard?
Why are you talking about it as if bad cables is an unavoidable fact affecting devices that happen to use these power supplies? Wouldn't you think the developers of these pan-european standard (and the similar chinese standard) would indeed have tweaked the output voltage of their standard if they would agree with you that the average micro USB cable would drop half a volt. They didn't because the average micro USB cable doesn't drop half a volt, even when the maximum current rated for these supplies, 1.8 A runs through them. They used the normal industry standard 5% variation for a reason! Micro USB cables do not normally drop half a volt, but only a couple of millivolts, a value comparable to the contact resistance of the gold plated micro USB connectors.

Yes there are cables on the market that are so piss poor that they do drop a couple of hundred millivolts, (0,1 to 0,3V seems to be typical for these) and if you already have a sub-par input voltage it can be an aggravating factor when used with a PI. These cables have been shown to have hair thin single strands of wire in them, sometimes not even copper wire, but aluminium! They are sold with the purest disregards for consumers. The only reason consumers still buy them is that small GSM phones can still be charged using these cables, even though it takes longer than normal. Cables like this are also used with fake Nokia (and other brand) chargers, with very poor and even dangerous electronics inside, there are not in any way specific to micro USB cables. an example of a piss poor PSU, that also uses piss poor cable (no coincidence there) can be found here: http://www.youtube.com/watch?v=T88ej64aXUM&feature=plcp.

And unfortunately yes, there are also PI's who's polyfuses seem to have had an "accident", and do not in any way have the resistance that one might expect of them, such PI's should be returned as defective, as I'm sure you would agree.
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by Dilligaf » Sat Dec 22, 2012 6:27 am
I'm just stating what I see day after day and that even a charger/power supply that meets the standards isn't guaranteed to work. I'm sure when they came up with the standard they were trying to stay within the usb specs which they did if you are directly powering a device but we are running that voltage through additional circuits before it makes it out the other end to the usb device, something I doubt they ever took into account. Why are you taking this so personally? Were you involved in setting up the standard?
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by Maxion » Sat Dec 22, 2012 9:01 am
mahjongg wrote:
Dilligaf wrote:You see, that's the problem a charger/supply that puts out 4.75-4.8 volts is in spec but by the time it gets to the guts of the PI it's under spec. The standard should be 5.0 to 5.25 or even 5.5 to make up for volt drops in cables etc.

The standard?
Why are you talking about it as if bad cables is an unavoidable fact affecting devices that happen to use these power supplies? Wouldn't you think the developers of these pan-european standard (and the similar chinese standard) would indeed have tweaked the output voltage of their standard if they would agree with you that the average micro USB cable would drop half a volt. They didn't because the average micro USB cable doesn't drop half a volt, even when the maximum current rated for these supplies, 1.8 A runs through them. They used the normal industry standard 5% variation for a reason! Micro USB cables do not normally drop half a volt, but only a couple of millivolts, a value comparable to the contact resistance of the gold plated micro USB connectors.

Yes there are cables on the market that are so piss poor that they do drop a couple of hundred millivolts, (0,1 to 0,3V seems to be typical for these) and if you already have a sub-par input voltage it can be an aggravating factor when used with a PI. These cables have been shown to have hair thin single strands of wire in them, sometimes not even copper wire, but aluminium! They are sold with the purest disregards for consumers. The only reason consumers still buy them is that small GSM phones can still be charged using these cables, even though it takes longer than normal. Cables like this are also used with fake Nokia (and other brand) chargers, with very poor and even dangerous electronics inside, there are not in any way specific to micro USB cables. an example of a piss poor PSU, that also uses piss poor cable (no coincidence there) can be found here: http://www.youtube.com/watch?v=T88ej64aXUM&feature=plcp.

And unfortunately yes, there are also PI's who's polyfuses seem to have had an "accident", and do not in any way have the resistance that one might expect of them, such PI's should be returned as defective, as I'm sure you would agree.


I'm sorry but you do seem to be in a bit of a fantasy land, talking about the future and chinese junk chargers.

The current situation is that the absolute majority of products you can buy that output 5v and contain either a USB socket or a micro-usb cable are all chargers, not power supplies.

The absolute majority of such products people have at home are all chargers, not power supplies.

I've tried USB chargers, real authentic came-with-the-product chargers in the 1A range, that SHOULD be able to power the pi without any peripherals without a hitch, yet they provide only 4.7-4.8V at 200mA.

There's no reason to talk about the future now, or what should be, but what IS.

Most people WILL NOT buy a new charger with the Pi since they think their current micro-usb charger should work. I mean hey, it's worked with EVERYTHING else they've used it for, why not the Pi?

I know of no appliance that requiers a very stable voltage that uses a USB port for power. All of these use barrel connectors or similar connectors. While it's not a standard, it is the de-facto standard.

This *IS* a problem.

It's not the micro-usb connector per-se, it's the fact that the Pi comes with no PSU and many of those chargers you can buy which according to their specs should be capable of keeping the PI alive don't. EVEN BRAND NAME CHARGERS.

I haven't found a single product with a USB socket or a micro usb cable in my country that's sold as a power supply.

Using a barrel connector instead would mean that you could find power *supplies* much, much more easily. My local electronic shops have racks and racks and racks of 5v power supplies. Hell, you can find them in many "Best Buy" type stores as well.

I don't see the confusion between USB charger and USB power supply ever going away, USB chargers will become even more common now that it's the cell phone charging standard in the EU but I know of no products except the Pi that use it as a power supply.

Instead of having intelligent discussion on this problem you keep bringing up the same things dismissing this issue entirely. Power issues are a *very* common problem on these forums, and almost always solved by changing the power supply to a better one.

Going with a barrel connector WOULD have been a better choice NOW. Most people who've got a case full of 5V PSU's have them because they've come with different products. Brand name USB harddrives, routers et. al. The majority of these supplies are of much better quality than the USB chargers around as they're rated for at least 2A.
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by aTao » Sat Dec 22, 2012 9:15 am
A charger IS a power supply. Saying it is not is like saying a car battery isnt a battery since it wont start a truck.

As connectors go the micro-USB is great and offers many advantages over barrel connectors (neither of which are a patch on the magnetic Apple power connectors).

If anything is going to fix the problem its the RPi suppliers source mains adapters that will work.
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by doveman » Sat Dec 22, 2012 9:44 am
I'd just say that using a 5v PSU doesn't always work either. I bought a Belkin 7-port hub which came with a 5v/4A PSU (Coming Data CP0540 http://www.ebay.com/itm/NEW-Coming-Data ... 0329163863 ) for £10, which I thought was a bargain for a hub and PSU that could power the RPi and all my peripherals.

However, the lead on the PSU was unusably short, so I had to extend it. When I checked the voltages I found

With nothing connected (not even the SD): 5.16v going in and the same across TP1-2.

With the SD card in, it dropped to 4.92v across TP1-2 and with the USB stick as well, 4.85-4.89v.

With the hub connected and the RF remote receiver plugged into that, it was down to 4.80-4.84v and with the Dual USB tuner added, 4.70-4.76v (4.9v going in at that point).

Plugging the PSU into the hub and powering the RPi from that via the microUSB gave me 4.44v across TP1-2 after it had settled down. The PSU output was about 4.92v.

I bought two of the hub/PSUs so had one with the original unaltered lead to test with and with that plugged into the hub, feeding the Pi via micro-usb, I read 4.68v across TP1-2 with the same peripherals, dropping to about 4.62v with the HDMI and LAN cables attached.

I've now bought a 12v PSU and putting that through a 5v UBEC I get around 4.93v at 95% CPU, with the UBEC feeding the RPi via GPIO and also splitting to power the hub. The PSU and UBEC only cost about £10 for both. I might have been able to spend less on the hub had I known there was no point getting the PSU.
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by Maxion » Sat Dec 22, 2012 11:05 am
doveman wrote:I've now bought a 12v PSU and putting that through a 5v UBEC I get around 4.93v at 95% CPU, with the UBEC feeding the RPi via GPIO and also splitting to power the hub. The PSU and UBEC only cost about £10 for both. I might have been able to spend less on the hub had I known there was no point getting the PSU.


I've also gone this route, but for different reasons. I need to power the Pi from a 12V battery so I needed the UBEC for that.

It, however, has many upsides. My Pi now has a barrel jack that I can use with any of the many 12V power supplies I have (tried em all, all work with 4.95V across TP1 & 2).

For anyone who needs stable 5V I'd recommend a 12V source and an UBEC.
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by aTao » Sat Dec 22, 2012 11:50 am
My, how time has moved on, new mnemonics and all, had to look up "UBEC".
Practical Wireless magazine published a battery eliminator circuit a while back. It consists of a battery clip and light bulb: when the light goes out the battery is eliminated.
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by doveman » Sat Dec 22, 2012 12:10 pm
Maxion wrote:I've also gone this route, but for different reasons. I need to power the Pi from a 12V battery so I needed the UBEC for that.

It, however, has many upsides. My Pi now has a barrel jack that I can use with any of the many 12V power supplies I have (tried em all, all work with 4.95V across TP1 & 2).

For anyone who needs stable 5V I'd recommend a 12V source and an UBEC.


Yeah, they're pretty good. I also used a 16v/4a laptop PSU whilst I was waiting for the 12v one and that worked fine as well. Probably overkill and no doubt would cost more to buy than the £5 for the 12v PSU but I had it lying around so it was handy to test with whilst I was waiting.
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by Maxion » Sat Dec 22, 2012 12:41 pm
doveman wrote:
Maxion wrote:I've also gone this route, but for different reasons. I need to power the Pi from a 12V battery so I needed the UBEC for that.

It, however, has many upsides. My Pi now has a barrel jack that I can use with any of the many 12V power supplies I have (tried em all, all work with 4.95V across TP1 & 2).

For anyone who needs stable 5V I'd recommend a 12V source and an UBEC.


Yeah, they're pretty good. I also used a 16v/4a laptop PSU whilst I was waiting for the 12v one and that worked fine as well. Probably overkill and no doubt would cost more to buy than the £5 for the 12v PSU but I had it lying around so it was handy to test with whilst I was waiting.


Yep, my UBEC (it's basically a switch-mode power converter) takes 1-40V input and turns it into 5V. Rated for 3A and based on the LM2596S chip from TI.
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by mahjongg » Sat Dec 22, 2012 6:43 pm
aTao wrote:A charger IS a power supply. Saying it is not is like saying a car battery isnt a battery since it wont start a truck.

As connectors go the micro-USB is great and offers many advantages over barrel connectors (neither of which are a patch on the magnetic Apple power connectors).

If anything is going to fix the problem its the RPi suppliers source mains adapters that will work.

No, a charger is a fundamentally different device than a power supply!
Its a bit hard to explain what the difference is between a charger and a power supply if you are unfamiliar with electronics.
The main difference is that any charging circuitry in for example a GSM phone doesn't mind what kind of input voltage it gets, as long as its above a minimum (mostly about 4V for chargers charging 3,7V accu's). So the designers of chargers do not care if the output of their designs drop a lot (much more than 5%). In fact for the charging circuit it is even beneficial if the input voltage drops when the circuit uses a lot of current. That way they have to dissipate less heat. That is the reason that the designers of the official iPhone chargers have indeed designed their charger to drop the output voltage sharply with increased current. Such a device isn't very suitable if any part of what it is powering cannot tolerate more than a 5% (0.25V) drop. While in fact the logic on the PI board itself can (most of it is powered from the regulated 3V3 supply anyway) its a different matter for USB devices! Most mice and keyboards will work with voltages as low as 4.4 Volt, but for example a WiFi adapter might not.

In contrast a real power supply measures what voltage its outputting, and regulates if to the required value. Logically there will always be some drop with higher currents (or the feedback circuitry has nothing to work with) but its is a very tiny change compared to any unregulated circuit, and will normally be much less than 5% of the nominal output voltage.

Some charger designs do not have any regulation, but their design is still robust enough that they can deliver say 1A without dropping their outputs too much. Technically we say that such supplies have "low internal resistance". That is why these are also nominally suitable for the PI under most circumstances.

P.S. I feel no need to reply to posters that I feel are simply trolling. Yes, there are some problems with the current power solution, but the situation is in no way as bad as they want to make it look like.

I will try to explain technical issues, but I will not play yes it is, no it isn't, games.

Also, unlike what some people construct me to be, im simply a moderator here, not an RFP member, and in no way I have any more influence on the decisions of the RPF than any other posters here. Except obviously trollers, which are recognized for what they are, and will most likely have no influence on any decision making. Them repeating the same points, exaggerated beyond recognition, over and over again isn't helpful. I do know though that the RPF is aware of whatever technical issues there are, and will do all it can to resolve them.
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by michele.x » Sat Dec 22, 2012 7:14 pm
mahjongg wrote:No, a charger is a fundamentally different device than a power supply!
Its a bit hard to explain what the difference is between a charger and a power supply if you are unfamiliar with electronics.
The main difference is that any charging circuitry in for example a GSM phone doesn't mind what kind of input voltage it gets, as long as its above a minimum (mostly about 4V for chargers charging 3,7V accu's). So the designers of chargers do not care if the output of their designs drop a lot (much more than 5%).

I have a nice example. I've a Yaesu two-way radio. I could charge the batteries either with the included battery charger or with a proper 13,5 V power supply. The battery charger is a wall wart unregulated 12V supply capable of 500 mA. The required specification for a power supply is 13,5V @ 2A, but the radio, if the power supply is stabilized and delivers 2A could work between 8V and 16V by design.

Trying to transmit with the battery charger normally make the the radio to shut off and stop the charging cycle.

So there's a difference between a charger and a power supply in peak current requirement and regulation, because a ni-cd battery has different requirements than a UHF power transistor.

The solution is to have an official Raspberry Pi power supply. Better a couple of models: one the classic black cube, and the other shoud have an illuminated purple and green Raspberry Pi logo on the top.
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by mahjongg » Sat Dec 22, 2012 7:22 pm
You are right, if the Raspberry PI could commission an official PSU then that would help a lot, but many people already have suitable power supplies laying around. Also an official PSU would probably cost a little bit more than whatever cheapest suitable PSU you could find, but for $6 or so it should be possible to source a suitable PSU that can be sold as official, and the RPF could assist in testing the suitability. For example E14 is already selling "suitable" PSU's for the PI, but I have no idea if they really tested them for suitability, or simply choose one in their assortiment that looked suitable.
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by tufty » Sat Dec 22, 2012 8:45 pm
mahjongg wrote:many people already have suitable power supplies laying around.

I've got a box full. Unfortunately, they have barrel jacks on them :)

In fact, most people *don't* have suitable power supplies lying about. Most of them have usb *chargers* lying about which happen to be more or less well enough regulated to work at the load levels they are exerting on them. If you go back to the link I posted earlier, you'll see what I mean. Even the iPad charger, which is considered to be pretty much a safe bet, starts dropping its output voltage as more current is drawn; 4.4V at 2.3A, and it's pretty much a straight line - even at 1A, which is easily achievable with a micro-wifi adaptor plugged in, you're looking at ~4.8V or so. Woops. Indeed, only 3 of the chargers tested show decent voltage regulation, but that's seemingly at the expense of a whole shedload of spikes, noise and ripple. None of them are anywhere near "clean", though.

So you have a bunch of "power supplies" which are "lying about" which might well work with the Pi idling, or with Pi + keyboard + mouse, but which approach the low voltage danger zone, and some random set of events might push them over the edge. I find it highly likely that power supply "borderline" issues are behind a significant part of the seemingly random USB issues people are seeing (particularly of the "plug in peripheral - boom" type), and that the actual problems in the USB stack are thus much harder to make out through the wall of noise.

So. What's the solution?

The most obvious one is to move power regulation back onboard, and go back to a 6-12V (or so) DC power supply. Unlikely to happen, though.
The only other one I can see is to mandate use of a properly regulated 5V USB power supply and make it extremely and prominently clear that the Pi is not guaranteed to work properly with J Random smartphone charger, no matter the perceived quality of the brand, and despite the fact it uses the same plug. Which also means that the Foundation need to recommend specific power supplies. Preferably, specific power supplies which are carried by Farnell and RS.

It's probably worth mentioning that direct-wiring USB power from the power in to the ports, which is a fairly common approach to bypassing those #(%&!@^% polyfuses might get enough juice to your high-power peripherals without tripping the polyfuse but if you don't have a really good PSU, it's still not going to solve everything.

Like I said before. The changes in the power supply side between prototype to delivered product was a really bad decision, made for all the right reasons. Hell is paved with good intentions.
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by mahjongg » Sat Dec 22, 2012 8:55 pm
Even the iPad charger, which is considered to be pretty much a safe bet, starts dropping its output voltage as more current is drawn
Like I said, this isn't a coincidence, or a "bad design". Real Apple chargers are quite complex, and its obvious that the dropping off of the voltage is quite intentional!

But it makes this kinds of chargers immediately unsuitable!

They should be listed in the wiki as "not working".

I agree that choosing the right supply is the real problem for unaware users, I disagree that the solution is to go back to a barrel connector, and larger than 8V input. That "solution" comes with its own set of problems, which may actually be worse than using the current solution, and a suitable PSU, and it also normally comes at considerable cost. But I don't want to repeat myself over and over again.

The real solution is to clear up which power solution (power supply) works and which one doesn't.
One solution I already have proposed is built detection of unsuitable power.
Other means could be:
  • a more strict official shortlist of multiple suitable supplies
  • a certification procedure with "certified for PI " labeling rights that could be withdrawn if the PSU is found not to be fit.

I am aware that adafruit already has a semi-officially certified as good for PI power supply, that is actually indeed suitable. They should be the first of hopefully many more that may get a certification label.
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by W. H. Heydt » Sat Dec 22, 2012 9:03 pm
mahjongg wrote:You are right, if the Raspberry PI could commission an official PSU then that would help a lot, but many people already have suitable power supplies laying around. Also an official PSU would probably cost a little bit more than whatever cheapest suitable PSU you could find, but for $6 or so it should be possible to source a suitable PSU that can be sold as official, and the RPF could assist in testing the suitability. For example E14 is already selling "suitable" PSU's for the PI, but I have no idea if they really tested them for suitability, or simply choose one in their assortiment that looked suitable.


I think there "sorta kinda" IS an "official" power supply...it's this one:
https://www.adafruit.com/products/501

I got a power supply to go with a Pi that is a gift to my grandson's cousins from MCM, this one:
http://www.mcmelectronics.com/product/28-13055
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by tufty » Sat Dec 22, 2012 9:20 pm
mahjongg wrote:They should be listed in the wiki as "not working".

Probably. Unfortunately, they work. Most of the time, at least.

mahjongg wrote:I disagree that the solution is to go back to a barrel connector, and larger than 8V input. That "solution" comes with its own set of problems, which may actually be worse than using the current solution, and a suitable PSU

Please enumerate the problems, as I simply don't see any apart from possible reversed polarity, and additional cost.

What I /do/ see is that the only real benefit of using Micro-USB PSUs, that the user probably has a suitable one lying about, is totally destroyed by the fact that the Micro-USB PSU the user has lying about is almost certain to not, in fact, be suitable. Despite the fact that it works perfectly with every other Micro-USB powered piece of equipment (s)he has. And that makes the Pi look really badly designed, in the same way that certain keyboards not working with the pi, despite working with every other USB host, makes the Pi look bad.
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by mahjongg » Sat Dec 22, 2012 9:48 pm
is almost certain to not, in fact, be suitable.

Why do you keep saying that! there might be a chance a random USB 1A power supply you already have laying around won't be suitable, granted, but "almost certain"?
I only agree with you when you are taling about those lightweight chargers for your Nokia GSM phone. then yes, I would throw them aside immediately as not suitable, but If you have a power supply for any device that uses an PSU with an USB port for power, (as opposed to for charging only, but most PSU's with USB type A ports won't be for charging only) then there is a very good chance it will power your PI too.

I repeat once more, the problems with using a barrel connector are:
  • Being forced to also add a regulator on board that can do at least 12V to 5V @1A
  • Also being forced to add protection against reverse polarity (not a big deal but in practice would prevent direct 5V powering with a barrel connector)
  • being forced to add a very big electrolytic capacitance, to prevent large ripple on the input
  • all this means, not being able to keep the dimensions of the PI as small as it is now, which also add costs and makes the PI less attractive.
  • Barrel connectors are also less reliable in letting through power without interruption during vibrations.
  • cost cost, and more cost, no way to keep the price at $35, which is the whole point!

Cost and dimensions have made the PI popular, demanding that the PI must be more expensive, bulkier and less power efficient (hotter) is what the competitors might like to happen to the PI.

The current situation may not be ideal, but it works!
And In fact, in the future the situation will only improve, and its reasonable workable now!
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by Maxion » Sat Dec 22, 2012 10:29 pm
mahjongg wrote:
is almost certain to not, in fact, be suitable.

Why do you keep saying that! there might be a chance a random USB 1A power supply you already have laying around won't be suitable, granted, but "almost certain"?
I only agree with you when you are taling about those lightweight chargers for your Nokia GSM phone. then yes, I would throw them aside immediately as not suitable, but If you have a power supply for any device that uses an PSU with an USB port for power, (as opposed to for charging only, but most PSU's with USB type A ports won't be for charging only) then there is a very good chance it will power your PI too.


*Who* has a USB *Power Supply*?! I've *Never* seen one marked power supply. All the ones I have are chargers. All the ones I've seen are chargers.

What product can you buy that comes with, or needs a power supply with a USB port?

mahjongg wrote:
is almost certain to not, in fact, be suitable.

I repeat once more, the problems with using a barrel connector are:
  • Being forced to also add a regulator on board that can do at least 12V to 5V @1A
  • Also being forced to add protection against reverse polarity (not a big deal but in practice would prevent direct 5V powering with a barrel connector)
  • being forced to add a very big electrolytic capacitance, to prevent large ripple on the input
  • all this means, not being able to keep the dimensions of the PI as small as it is now, which also add costs and makes the PI less attractive.
  • Barrel connectors are also less reliable in letting through power without interruption during vibrations.
  • cost cost, and more cost, no way to keep the price at $35, which is the whole point!


What's the problem with raising the cost by 5$ if that means you can actually find a working PSU lying around?
Show me one USB power supply that actually outputs 5V at it's rated A for 5$ and I'll show you 10 5V barrel connector PSU's that do the same.
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