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HawaiianPi
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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 11:33 am

tkaiser wrote:
Sun Mar 18, 2018 1:53 am
For the censors/moderators: it's stupid to delete my post :)
...
MOD: Didn't delete it, just removed the offensive comment and banned you for a week. Is that OK?
Image

By the way, I did check out that thread he referenced and I was able to run the test posted their several times in rapid succession with no heatsink or fan, without any power or thermal throttling issues. So once again, µUSB works just fine, provided you have a good PSU on the other end.
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paulslocum
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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 11:40 am

Use a power supply that is up to the job.
I think a big part of the problem is that the majority of micro USB cables can't deliver enough power even if you have a properly rated power supply. We're about to release a Pi product and I bought quite a lot of different USB cables before I finally found a brand that consistently works. Even cables that are rated for "fast charging" are sometimes not consistent enough.

Also many of the cheaper USB power supplies are not consistently made. I've found that 1 in 5 or maybe 1 in 10 of popular 2-2.5 amp power supplies on Amazon don't deliver the rated power. For consistency, you have to shell out $10 for a really good USB power supply from Mouser.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 11:44 am

tkaiser wrote:
Sun Mar 18, 2018 11:32 am
Imperf3kt wrote:
Sun Mar 18, 2018 11:24 am
People focus on the current and not the voltage, because the current matters, not the voltage.
Funny. What was the maximum consumption you've ever seen when using an RPi? More than 9W?

For Micro USB maximum current rating do a simple web search for Micro-USB_1_01.pdf.
Well, I could search for that old document, or I could just search for micro USB current rating where I find that RS do a micro USB 2.0 socket that is rated at 3.0A. I imagine they are not the only ones that don't use an old "standard".

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 11:48 am

HawaiianPi wrote:
Sun Mar 18, 2018 11:33 am
So once again, µUSB works just fine, provided you have a good PSU on the other end.
Adding to 'good PSU' the cable between both cable ends is what matters. So yes, if you use the great power supply RPi sells, then you're not running in issues (BTW: the RPi PSU is my general recommendation for any SBC that uses Micro USB since inexpensive and great quality)

The issue is called 'voltage drop under load' and current ratings above 1.8A are irrelevant since as far as I know and have tested you are not able to feed that high amounts of current to your Pi anyway. Ohm's law exists and is valid even on Raspberry Pis :)

If even most experienced RPi users like Dougie Lawson suffer from this problem (under-voltage --> frequency capping) how can we talk about 'µUSB works just fine'? The whole power circuitry seems to be a try to compensate for the real problem. That's cable and contact resistance, that's the firmware doing frequency capping, that's peripherals getting under-volted.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 11:55 am

rpdom wrote:
Sun Mar 18, 2018 11:44 am
Well, I could search for that old document, or I could just search for micro USB current rating where I find that RS do a micro USB 2.0 socket that is rated at 3.0A. I imagine they are not the only ones that don't use an old "standard".
How should ignorance help solving problems? Please have a look at Ohm's law. Somewhat oversimplifying: you get either 5V or 2.5A but not both at the same time with those tiny contacts in the Micro USB receptacle and insufficient soldering on the PCB. The problem still is under-voltage.

Anyway: what is the maximum consumption you have seen with your RPi so far? Exceeding 9W or not?

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 11:56 am

Also, I just wanted to say that despite the issues with power supplies and cables, I love the micro USB power connector and wouldn't trade it for anything else. The ability to buy separate power supplies and cables in a variety of lengths, colors, and styles is incredible for our applications. It's also great that you can often power them from the USB ports on the back of TVs. I've found that it often works fine if you have a good micro USB cable.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 12:07 pm

tkaiser wrote:
Sun Mar 18, 2018 11:32 am
Imperf3kt wrote:
Sun Mar 18, 2018 11:24 am
People focus on the current and not the voltage, because the current matters, not the voltage.
Funny. What was the maximum consumption you've ever seen when using an RPi? More than 9W?
2.886w from a Pi3B, according to https://www.rapidtables.com/calc/electr ... lator.html
I was pushing the Pi as hard as I possibly could because I was intentionally trying to see at what point it failed when powered by [email protected]
Sadly, it did not fail and my Pi worked just fine, drawing a maximum of 0.56A
I do doubt that the method I was using is the best way to test (setting all four cores to 100% load) so I plan to perform different tests in the future.
tkaiser wrote:
Sun Mar 18, 2018 11:32 am
For Micro USB maximum current rating do a simple web search for Micro-USB_1_01.pdf.
You may note that that document is dated 2007.
Here's one from 2016:
PD Micro-A, PD Micro-AB, and PD Micro-B connectors shall be capable of carrying 3A current as specified in
Section 3.6.5.1
...
3.6.5.1 3A PD Connector Mated Pair (EIA 364-70, Method 2)
When a current of 3.0 A is applied to the VBUS pin and its corresponding GND pin (i.e., pin 1 and pin 5 of the PD Micro-A
Connector, PD Micro-AB Connector, or PD Micro-B Connector), the delta temperature shall not exceed +30°C at any
point on the connectors under test, when measured at an ambient temperature of 25°C.
USB_PD_R2_0 V1.2 -20160325.pdf
the document appears to imply the maximum current for MicroUSB receptacles is actually 5A
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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 12:23 pm

tkaiser wrote:
Sun Mar 18, 2018 11:48 am
If even most experienced RPi users like Dougie Lawson suffer from this problem (under-voltage --> frequency capping) how can we talk about 'µUSB works just fine'?
Because I ran the exact same test without issue. Several times in rapid succession, in fact, with no thermal or power throttling on my 3B+.

viewtopic.php?p=1287753#p1287753

The problem is NOT the µUSB connector. It's the PSU, the µUSB cable, or both. If you have a good PSU and cable, it works.

No one is denying the new 3B+ needs more juice, but saying that it's the fault of the connector is just nonsense. :roll:
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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 12:26 pm

tkaiser,
...have a look at Ohm's law.
OK. Let's do that.

I pulled two USB cables out of my junk box at random. I measure about 0.1 Ohm, each way, along those cables. Admittedly my meter does not resolve well at those values.

So I'd expect a 0.2 voltage drop for a Pi drawing 1A. 0.4V at 2A.

Ergo I expect my supplies putting out 5.2V are just fine.

What do you mean "insufficient soldering on the PCB"? It's fine for its purpose.
Memory in C++ is a leaky abstraction .

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 12:32 pm

Imperf3kt wrote:
Sun Mar 18, 2018 12:07 pm
You may note that that document is dated 2007.
Here's one from 2012
You can't fix a specification by using another totally irrelevant. USB PD (power delivery) is a new and great spec that deals with higher amperage ratings and even defines higher voltages since 5V is a joke with high currents since both cable and contact resistance is too high and the voltage available at the other end of the cable will drop too much (again: the problem is 'voltage-drop under load')

You do not try to push more than a few A through circuitry at 5V since it's a bad idea (again: Ohm's law). The USB PD specs define a maximum of 2A at 5V, for any higher amperage rating the voltage has to be increased too since you do not use 5V with high currents anyway.

See here for some details and the 5 profiles: http://www.electronicdesign.com/interco ... r-delivery

So if a device wants to be compliant to USB PD it needs to implement at least Profile 1 and new receptacles and cables are needed. The maximum current rating of an PD compliant Micro USB receptacle/plug is 3A but this is only allowed with 12V or 20V. So while such a PD compliant Micro USB connection using new cables and connectors is good for 3A no one right in his mind does try to implement this at 5V since... voltage drop too high.

Anyway, this whole spec stuff doesn't really matter since in reality based on my and other tests you can't exceed 9W consumption with the Pi and this is well within the Micro USB specs (5V / 1.8A). Still the problem is usually under-voltage (the lower the voltage the more cable/contact resistance becomes a problem --> voltage drops) but users are usually not aware. Those with a display seeing the yellow lightning bold might get the idea they ran into under-voltage but are told to upgrade to higher amperage ratings. Replacing their PSU usually then fixes the problem by accident (better cable between PSU and board).

Headless users usually don't take notice but if I understood @jamesh right, Pi Foundation wants to fix this: viewtopic.php?f=63&t=208057&p=1287779#p1287779

If you want to test for the limits by CPU utilization you would need to use something heavy. Stress, sysbench is all pretty lightweight stuff. You need to get cpuburn-a53 for example (and with a Pi 3 then run for sure into under-voltage being frequency capped at 600 MHz): viewtopic.php?f=63&t=208057&p=1287349#p1287276

Edit: The Pi is not PD compliant of course and I don't think PD compliance is of any use since only increasing the costs. With USB-C (cables and receptacles made for up to 3A by design while Micro USB receptacles are rated for 1.8A max and 'average' USB cables only made for 500mA --> voltage drop) there exist two true 5V modes with 1.5A and 3A that only require some primitive negotiation. That's the way to go in the future and then this future Pi might also be used to reliably power external disks and such stuff... at the moment with that input circuitry that's gambling :)

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 12:57 pm

Heater wrote:
Sun Mar 18, 2018 12:26 pm
Ergo I expect my supplies putting out 5.2V are just fine.
If you provide 5.2V at the PSU and then try to draw 9W (5V/1.8A) from the RPi (using an external disk for example with CPU loads you can't do this since frequency capping reducing consumption greatly once input voltage drops below 4.65V) which voltage do you measure at pins 4 and 6 of the GPIO connector? 4.5V? 4.4V? Less?

The whole power circuitry seems not to be made for more than ~1.5A anyway and I ask myself why? Maybe since powering through Micro USB is such a mess with all those 'average' cables out there and people using phone or smart chargers so both under-voltage and limited current (e.g. only providing 500 mA from 'smart' chargers or USB2 ports) become a problem.

The under-voltage detection stuff added on the 2nd gen Raspberries greatly mitigates the problem by downclocking everything in such situations but it only masquerades the problem. IMO a real fix would've been a good barrel connector able to reliably provide more than 2A to board plus peripherals avoiding the usual under-voltage drama with the Pi today when overall consumption exceeds 5W.

Anyway, let's hope for the best (USB-C) with next gen Pi and let's hope that more users are aware of their boards running under-volted / frequency capped.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 1:02 pm

I have two Pi projects that I run from 2.1 mm Barrel jack power supplies. I have one of these, https://www.adafruit.com/product/658 5V 10A switching power supplies that I use with my bread board rig. It has a 3B and a Pi foundation 7 inch touch screen. Plus some other odds and ends. It's a portable setup that moves around the house some. 10A is a bit of overkill but it runs nice and cool and I don't have to worry about ever overloading it. Made up my own custom power cables to feed the Pi etc. And Poly fuses where I deemed necessary.
I also have one of these, https://www.adafruit.com/product/1466 5V 4A switching power supply that powers a portable Pi with a battery charger (powerboost 1000c) in it. Its a Pi A+ with Sense Hat and some other sensors connected. I went with 4 A so I can run it and charge the battery at the same time without the power supply getting hot etc..
I find the barrel connector so much easier to plug and unplug, which I do quit frequently with these two setups. Also more robust than the Micro USB port IMHO. No plugging in upside down, or trying to, etc. Quick and easy. For what its worth, I have numerous devices around the house with barrel power connectors and various different voltages. I have yet to ever plug the wrong charger into the wrong device. YMMV of course.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 1:14 pm

tkaiser wrote:
Sun Mar 18, 2018 12:57 pm
Heater wrote:
Sun Mar 18, 2018 12:26 pm
Ergo I expect my supplies putting out 5.2V are just fine.
If you provide 5.2V at the PSU and then try to draw 9W (5V/1.8A) from the RPi (using an external disk for example with CPU loads you can't do this since frequency capping reducing consumption greatly once input voltage drops below 4.65V) which voltage do you measure at pins 4 and 6 of the GPIO connector? 4.5V? 4.4V? Less?

The whole power circuitry seems not to be made for more than ~1.5A anyway and I ask myself why? Maybe since powering through Micro USB is such a mess with all those 'average' cables out there and people using phone or smart chargers so both under-voltage and limited current (e.g. only providing 500 mA from 'smart' chargers or USB2 ports) become a problem.

The under-voltage detection stuff added on the 2nd gen Raspberries greatly mitigates the problem by downclocking everything in such situations but it only masquerades the problem. IMO a real fix would've been a good barrel connector able to reliably provide more than 2A to board plus peripherals avoiding the usual under-voltage drama with the Pi today when overall consumption exceeds 5W.

Anyway, let's hope for the best (USB-C) with next gen Pi and let's hope that more users are aware of their boards running under-volted / frequency capped.
On my bread board Pi setup I mentioned above, I made up my own custom USB cables. On the end that plugs into the Pi's USB port, only the Data + - and Ground wires are connected. On the device end the +5V comes from my power supply though a 500ma Poly fuse. Data comes from the Pi but power comes from my power supply. Completely bypassing any current limitation the Pi might impose.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 3:45 pm

Heater wrote:
Sun Mar 18, 2018 11:05 am
I have here dozens of SBC's, dev boards and other gadgets that get their power from barrel jacks. To go with them I have a box full of power bricks with barrel connectors. They have been collected over many years. I'm pretty sure they are all different. The connectors are different diameters and various lengths. Very similar looking barrel connectors do not fit into the same jack. And of course they are all different voltages. 5, 6, 12, 15, 24 etc, etc.

This chaos has been driving me nuts for years. And here you are suggesting the Pi adopt the same chaos!
IIRC, that problem--just at 5v, or thereabouts, is what drove the EU to try to mandate that *all* cell phones use a standard charging connector. The idea being to stop dumping vast number of unused chargers into land fills. The only holdout has been Apple. As it is, my older PSUs--1A, 2A--are still useful to me. At a recent convention at which I was in charge of Convention Registration, I was charging 5 different devices--3 batteries, a tablet, and a cell phone--over night in my room to be ready to go the next day. I was doing it using Pi PSUs of various vintages. My limit on how many devices I could charge had more to do with how many outlets I could set up than how many PSUs I had on hand.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 3:48 pm

davidcoton wrote:
Sun Mar 18, 2018 9:15 am
Imperf3kt wrote: If someone could please instruct me on which is the "standard", I'll start using it right away!
That's good. None of them are standard, don't use any of them :lol:
Standards are a wonderful thing. There are so many to choose from...

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 3:57 pm

tkaiser wrote:
Sun Mar 18, 2018 11:23 am
Seriously: What is the highest consumption you've seen with a Pi so far? Me not more than 9W drawn from the wall.
Measuring the power "at the wall" is meaningless. You're adding in any lack of efficiency of the PSU itself. You need to measure your total power at the Pi.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 7:43 pm

tkaiser wrote:
Sat Mar 17, 2018 5:12 pm
scruss wrote:
Sat Mar 17, 2018 3:41 pm
mcsk wrote:
Sat Mar 17, 2018 12:04 pm
… the standard DC power connector?
Which one is the standard? There are at least 52 sizes to choose from.
Me not joining discussions about Micro USB for powering so just providing this bit of information related to somewhat 'popular' SBC:
1) Sony PSP used 4.00/1.70 mm and this connector is also used on Cubieboards, Banana Pi, NanoPi and Orange Pi (or Micro USB)
2) All Minnowboard, Wandboard, Olimex and the larger ODROIDs use 5.50/2.10 mm
3) All older ODROIDs (up to and including C2) use 2.50/0.80 mm
4) All Pine64/Rock64 boards except the first one use 3.50/1.35 mm

Always centre positive. Back at the time when I had +40 different SBC laying around I was totally fine with 5 different PSUs (4 x barrel and Micro USB).

Problems:
1) If you don't realize you need the specific PSU with this barrel plug you end up buying on eBay a 'PSP USB power cable', some of them showing a 'nice' voltage drop under load
2) 12V PSU with the same 5.5/2.1 mm connector exist. A good way to fry your board
3) Same as 1) but getting this specific USB cable with an 2.5/08mm connector at the other end is even harder
4) Same as 3)

Unlike Raspberries not a single other SBC around using Micro USB provides some sort of under-voltage protection and/or signaling. And this (frequency capping when input voltage drops below 4.65V as it's implemented on Raspberries starting with the 2nd generation) is IMO the real reason why Micro USB somewhat works here...

BTW: What is the highest amount of current drawn by a RPi when powered through Micro USB so far? Curious since I've never seen this exceeding 1.8A at the wall (PSU included then of course).
Did you actually measure 1.8A "at the wall"? 2.5A @ 5V is 12.5W. Assuming max current draw. 12.5W divided by 120V is 0.104 A at the wall plug. 100ma. A little more than that if you factor in the lose of the power supply. It's half that if your mains are 240 volts.
1.8A times 120 V is 216 watts?

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 7:58 pm

W. H. Heydt wrote:
Sun Mar 18, 2018 3:48 pm
Standards are a wonderful thing. There are so many to choose from...
Image
https://xkcd.com/927/
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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 8:14 pm

I think this one of those, "you can please most of the people most of the time, but not all of the people all of the time" scenarios.
You can however convert Micro USB to barrel if you have a mind to. There are adapter cables out there. https://www.adafruit.com/product/2727 Or you can roll your own with a soldering iron etc, like I did..

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Re: Micro USB for powering PI is no longer OK

Sun Mar 18, 2018 8:46 pm

alphanumeric wrote:
Sun Mar 18, 2018 7:43 pm
Did you actually measure 1.8A "at the wall"? 2.5A @ 5V is 12.5W. Assuming max current draw. 12.5W divided by 120V is 0.104 A at the wall plug. 100ma. A little more than that if you factor in the lose of the power supply. It's half that if your mains are 240 volts.
1.8A times 120 V is 216 watts?
Don't forget the conversion from DC to AC...which involves the square root of 2 to get the RMS value. See my earlier post in this thread about how much power 1.8A at 117 volts actually is.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 25, 2018 3:25 pm

W. H. Heydt wrote:
Sun Mar 18, 2018 3:57 pm
tkaiser wrote:
Sun Mar 18, 2018 11:23 am
Seriously: What is the highest consumption you've seen with a Pi so far? Me not more than 9W drawn from the wall.
Measuring the power "at the wall" is meaningless. You're adding in any lack of efficiency of the PSU itself. You need to measure your total power at the Pi.
When I measure 9W "at the wall" does this mean 1.8A "at the Pi" or less? The latter of course. So not even 1.8A are able to be drawn by a Pi. Which is a problem given that 1.2A should be provided to consumers on the USB bus and the Pi itself also needs some juice.

That's the direct result of powering through Micro USB which is simply insufficient. Problem known since the first Pi but never fixed but only masqueraded instead (the yellow lightning bolt, headless users never see and then wonder why they're running frequency capped all the time, see here or here or there)

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Re: Micro USB for powering PI is no longer OK

Sun Mar 25, 2018 3:46 pm

tkaiser wrote:
Sun Mar 25, 2018 3:25 pm
When I measure 9W "at the wall" does this mean 1.8A "at the Pi" or less? The latter of course. So not even 1.8A are able to be drawn by a Pi. Which is a problem given that 1.2A should be provided to consumers on the USB bus and the Pi itself also needs some juice.
At the wall, 9W is going have a current so low that the accuracy of the reading is suspect. Farther along, yes, the Pi will be getting less than 1.8W (at 5v), but it may not need more than that, depending on what is being done and what is attached. Remember that a device will only draw the power required to run. It won't draw extra power just because it can. Even taking all of that into account, it doesn't make a case that there is a problem with the uUSB connector. Aside from the Pi's own load issues, you may have an inadequate or completely inefficient PSU or a bad cable. Again, the "9W from the wall" tells you essentially nothing about what is going on. What is the power draw at the Pi?

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Re: Micro USB for powering PI is no longer OK

Sun Mar 25, 2018 3:47 pm

tkaiser wrote:
Sun Mar 25, 2018 3:25 pm
That's the direct result of powering through Micro USB which is simply insufficient. Problem known since the first Pi but never fixed but only masqueraded instead (the yellow lightning bolt, headless users never see and then wonder why they're running frequency capped all the time, see here or here or there)
the problems you are quoting are NOT related to contact resistance of the microUSB cable, but are related to the thickness of the wires of the microUSB cable. A thin cable can have several tenths of an Ohm resistance while contact resistance of the gold plated contacts of a microUSB connector is only expressed in micro Ohms (thousands of an Ohm) typically 30mOhm, while its true that these connectors are rated (that is guaranteed to work) for 1.8 Ampere, (to comply with USB 2.0 Specs) there is no solid technical reason to think that at 2.5A they would fail. for at that peak current only 75mW would be dissipated in the contact. Also, if manufacturers would expect microUSB connectors to fail at 2.5A, why would they use microUSB with power supplies that deliver that amount of current, or more. Note that USB 3.0 connectors use even smaller contact pads, and they are rated with even higher currents.

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Re: Micro USB for powering PI is no longer OK

Sun Mar 25, 2018 4:02 pm

mahjongg wrote:
Sun Mar 25, 2018 3:47 pm
the problems you are quoting are NOT related to contact resistance of the microUSB cable, but are related to the thickness of the wires of the microUSB cable.
Even users with official RPi 3 PSU are affected: https://github.com/bamarni/pi64/issues/ ... -374950032 but I agree that's usually the cable that results in the voltage drop.

In general it's really as easy as this: Using Micro USB to power a board is encouraging users to do it wrongly:

1) they use insufficient phone chargers that provide only 500 mA since the Pi is not compliant to any 'quick charging' specs or USB PD and therefore able to tell a 'smart' charger that more than 500 mA are needed
2) they use any average (crappy) Micro USB cable resulting in voltage drops, frequency capping or even brown-outs

As a consequence users should be aware of this problem and should at least buy official PSU. Since buying a 'special' PSU is mandatory to have fun with the Pi (or to prevent the countless under-powering hassles) this PSU could also use a sane barrel plug. As listed in this thread there are a few barrel plugs that are dangerous (the 5.5mm types since almost everywhere there are 12V PSUs lying around using these jacks) so by choosing eg. 4/1.7mm and providing a mandatory PSU with this plug the problem would be solved already.

Then it would also be possible to feed the Pi with 2.5A or even slightly more so host-powered 2.5" disks wouldn't be a problem any more. Currently at least with the Pi 3 it's not possible without a very special PSU (exceeding 5.5V) to feed more than 1.5A anyway (the voltage drop then gets insanely severe so under-voltage protection kicks in)

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Re: Micro USB for powering PI is no longer OK

Sun Mar 25, 2018 4:15 pm

Your "sane barel plug" is completely insane when you are talking about contact resistance, a typical barrel plug uses nickel plating, which means it has much worse contact resistance than a much more modern gold plated solution. The only reason it has a high current rating is because it has a much higher mass than a typical USB connector, that doesn't mean its current rating is useful in this case, as its contact resistance (voltage loss) is still much higher, also it has much higher chance of current interruptions due to movement of the cable, (contact failure). Using a primitive barrel connector is like going back to the middle-ages.

That, and the fact that using a barrel jack invites incidents like plugging in AC or 27V DC carrying power supplies. Its was and is a completely unsuitable power connector for a PI.

No, using a modern gold plated connector like microUSB is perhaps not a perfect, but is a much-much better solution.

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