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weust
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 3:00 pm

Hand mods sound good to me, in my use case.

Thanks for the update.

drgeoff
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 3:33 pm

raspy1 wrote:
Mon Sep 10, 2018 8:03 pm
An extra question: is anyone knows if there is a power priority management if both 5V PSU & PoE are connected?
I can't see that is any different from powering via the micro-USB socket and the GPIO header at the same time.

There is no sensing upwind of the output side of the polyfuse which could be used to know that both micro-USB and GPIO header (PoE HAT if fitted) are powered. And even if there was there is no controllable switch on the micro-USB input to turn off supply of power from there.

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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 5:13 pm

drgeoff wrote:
Tue Sep 11, 2018 3:33 pm
raspy1 wrote:
Mon Sep 10, 2018 8:03 pm
An extra question: is anyone knows if there is a power priority management if both 5V PSU & PoE are connected?
I can't see that is any different from powering via the micro-USB socket and the GPIO header at the same time.

There is no sensing upwind of the output side of the polyfuse which could be used to know that both micro-USB and GPIO header (PoE HAT if fitted) are powered. And even if there was there is no controllable switch on the micro-USB input to turn off supply of power from there.
No there is some prioritisation going on here, though how/what/where will need to be explained by others.

If I power up the Pi with PoE then connect a micro USB power supply, then disconnect the USB, the hat power cycles. Removing the network cable doesn't cause the Pi to power cycle. The network switch shows that as soon as I connect the micro USB Power supply it stops delivering power over Ethernet.
If I power up the Pi with Micro USB power supply and then add the Ethernet Cable, power is only drawn from the Micro USB supply, at least as reported by my PoE Switch.

Martin

Roken
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 5:31 pm

I'm not an electronics guy, and home spun fixes won't work. However, I'd rather replace than refund (at the moment, on the Pi I have it on, it's not the end of the world. No USB - or indeed any connected peripherals at all. Dedicated Plex server reading from an NFS drive). The other PIs, however, would be a different matter, since one has the NFS drives plugged in, and one is Retro - with a full complement of mouse, KB, game controller and HDMI.

My plan is all three will be PoE. So what's the ETA on unencumbered models?
Headless PI. OMG, someone cut it's head off. Oh, hang on. it didn't have one to start with.

hippy
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 5:40 pm

drgeoff wrote:
Tue Sep 11, 2018 3:33 pm
raspy1 wrote:
Mon Sep 10, 2018 8:03 pm
An extra question: is anyone knows if there is a power priority management if both 5V PSU & PoE are connected?
I can't see that is any different from powering via the micro-USB socket and the GPIO header at the same time.
Nor could I which is why I previously asked if it was possible to power the Pi from both micro-USB and PoE amongst other usage scenarios -

https://www.raspberrypi.org/forums/view ... 5&t=220781

On Pi's previous to the 3B+ there was an ideal diode which AIUI protected against being simultaneously powered by micro-USB and GPIO pins. On the Pi 3B+ that's gone so, as with Zeroes, simultaneously powering through micro-USB and GPIO pins is a bad idea.

Because the Pi can be simultaneously powered by micro-USB and PoE I am guessing that ideal diode, or something like it, has been included on the PoE HAT. Unfortunately there are no schematics of the PoE HAT published so I cannot check that is the case.

If there is an ideal diode or similar on the PoE HAT I guess the priority of micro-USB and PoE HAT powering would come down to which was delivering the highest voltage.

^ Actually, no, it cannot be like that.

If power goes in via micro-USB it goes to 'everywhere' on the Pi 3B+. If 5V is present on the Pi then the PoE must not provide any power to the Pi or there can be a voltage imbalance between the two, so the priority would have to be micro-USB if present.
Last edited by hippy on Tue Sep 11, 2018 5:52 pm, edited 1 time in total.

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Burngate
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 5:50 pm

If there's a diode, ideal or not, on the PoE HAT, then a higher voltage on the u-USB would take precedence.

But higher voltage out of the PoE risks putting current back out of the u-USB

Why they decided the ideal diode wasn't required, I don't know, since they intentionally put it in on the 3B and previous

hippy
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 5:54 pm

Burngate wrote:
Tue Sep 11, 2018 5:50 pm
But higher voltage out of the PoE risks putting current back out of the u-USB
Correct. I just realised that and was updating my post to correct that while you were posting.

Power through micro-USB has to take precedence. The post by martinrowan above suggest that it does. If it doesn't that might be something else they might like to fix.

drgeoff
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 6:26 pm

martinrowan wrote:
Tue Sep 11, 2018 5:13 pm
drgeoff wrote:
Tue Sep 11, 2018 3:33 pm
raspy1 wrote:
Mon Sep 10, 2018 8:03 pm
An extra question: is anyone knows if there is a power priority management if both 5V PSU & PoE are connected?
I can't see that is any different from powering via the micro-USB socket and the GPIO header at the same time.

There is no sensing upwind of the output side of the polyfuse which could be used to know that both micro-USB and GPIO header (PoE HAT if fitted) are powered. And even if there was there is no controllable switch on the micro-USB input to turn off supply of power from there.
No there is some prioritisation going on here, though how/what/where will need to be explained by others.
I chose my words carefully and did not say "no prioritisation". Nor am I saying that there is prioritisation. I did explain that there is no way to interrupt the input from the micro-USB socket.

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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 7:16 pm

Roken wrote:
Tue Sep 11, 2018 5:31 pm
I'm not an electronics guy, and home spun fixes won't work. However, I'd rather replace than refund (at the moment, on the Pi I have it on, it's not the end of the world. No USB - or indeed any connected peripherals at all. Dedicated Plex server reading from an NFS drive). The other PIs, however, would be a different matter, since one has the NFS drives plugged in, and one is Retro - with a full complement of mouse, KB, game controller and HDMI.

My plan is all three will be PoE. So what's the ETA on unencumbered models?
I am presuming here, but I doubt we will be making any more until the fix is in! How long that takes toget through the supply chain I do not know.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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raspy1
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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 7:30 pm

Thanks for interesting answers, tests and debate regarding power between the 2 sources.

About the original issue of the PoE HAT, the engineering suggest some RPI 3B+ hardware are not impacted:
one of the two brands of USB current limiting switch
-> Is it possible to identify the component (software test, hw vendor logo?) for our existing RPI 3B+?
-> and maybe ask the dealers to create a specific ref to order the non affected RPI 3B+ that could be compliant with the PoE HAT?

And last point, it will be great to have schematic & component values (which cap to remove / capacitor & coil value and cut + soldering points) for the two suggested workarounds :
- Removing reservoir caps from the main board (an easy, clean mod if you can use a soldering iron, but limits USB hotpluggability).
- Inserting a small amount of series impedance in the current path from the HAT (this one will be a bit fiddly to implement).
We are now on the right way :)

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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 7:43 pm

raspy1 wrote:
Tue Sep 11, 2018 7:30 pm
Thanks for interesting answers, tests and debate regarding power between the 2 sources.

About the original issue of the PoE HAT, the engineering suggest some RPI 3B+ hardware are not impacted:
one of the two brands of USB current limiting switch
-> Is it possible to identify the component (software test, hw vendor logo?) for our existing RPI 3B+?
-> and maybe ask the dealers to create a specific ref to order the non affected RPI 3B+ that could be compliant with the PoE HAT?

And last point, it will be great to have schematic & component values (which cap to remove / capacitor & coil value and cut + soldering points) for the two suggested workarounds :
- Removing reservoir caps from the main board (an easy, clean mod if you can use a soldering iron, but limits USB hotpluggability).
- Inserting a small amount of series impedance in the current path from the HAT (this one will be a bit fiddly to implement).
We are now on the right way :)
Think there is going to be a blog post in the next few days which should have more detail.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

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Re: PoE HAT - USB Ports not working - over-current

Tue Sep 11, 2018 9:37 pm

raspy1 wrote:
Tue Sep 11, 2018 7:30 pm
Thanks for interesting answers, tests and debate regarding power between the 2 sources.

About the original issue of the PoE HAT, the engineering suggest some RPI 3B+ hardware are not impacted:
one of the two brands of USB current limiting switch
-> Is it possible to identify the component (software test, hw vendor logo?) for our existing RPI 3B+?
-> and maybe ask the dealers to create a specific ref to order the non affected RPI 3B+ that could be compliant with the PoE HAT?
The USB power switch is pretty much an industry standard form-factor for package and function, with multiple vendors providing functionally equivalent components. It's why we picked it in the first place - it's not unique to a manufacturer so competition drives the price down.

As we've previously specified the two nominated manufacturers offerings as equivalent, successive batches of Pi 3B+ will have been built with either manufacturer's parts.

There's no obvious visual difference between the two parts. There will be top laser markings on the package that will be "different" between manufacturers but that's hard to translate into which manufacturer this part came from, as they encode batch/lot number and not part number.

And last point, it will be great to have schematic & component values (which cap to remove / capacitor & coil value and cut + soldering points) for the two suggested workarounds :
- Removing reservoir caps from the main board (an easy, clean mod if you can use a soldering iron, but limits USB hotpluggability).
- Inserting a small amount of series impedance in the current path from the HAT (this one will be a bit fiddly to implement).
We are now on the right way :)
The modification debate is still in the air. There are multiple conflicting factors at work that means any user-implemented mod we document needs to be carefully thought through and tested both in the lab and in the field.
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daytona
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 7:17 am

Because the regulator operates at a fairly low frequency, each time it switches it moves quite a large chunk of energy into the three USB reservoir caps via the current limiting switch: this large instantaneous current is fooling the switch into thinking that a genuine over-current event is occurring.
This reads like there is insufficient filtering (capacitance) on the output of the PoE Hat regulator so the ripple on the 5 volt output from the HAT is making its way to the USB reservoir caps which are then also working as filter caps for the 5 volt supply.

So where I, and others have added an additional capacitor to the output on the PoE Hat (bringing it up to, or above the value shown on the MP8007 reference design) the 5 volt supply is then filtered enough before it gets to the Pi and the USB reservoir caps aren't trying to smooth the large ripple on the 5 volt supply.

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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 7:25 am

I'm really pleased to see the comprehensive response to the Register and the repost here. The upcoming blog will hopefully be even more enlightening. With respect to one line segment of the response:
jamesh wrote:
Tue Sep 11, 2018 2:22 pm
We missed it in product testing because (dumb luck) our heavy-load testing was done on boards with the other brand of switch, and most of our field testers were only using the board to power mice and keyboards, which works fine on all the HAT/Pi pairs we've tested.
This sort of makes sense, with the exception that I (and others) have reported the over-current warnings being triggered without any device being attached to the USB ports and my initial report of the problem was experienced with just a Logitech wireless keyboard/mouse adaptor, which I'd expect to be fairly low current (though I don't have a USB power tester to measure it).

So in the release to the field, problems were seen even at zero and low load. Just an observation.

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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 12:28 pm

martinrowan wrote:
Wed Sep 12, 2018 7:25 am
I'm really pleased to see the comprehensive response to the Register and the repost here. The upcoming blog will hopefully be even more enlightening. With respect to one line segment of the response:
jamesh wrote:
Tue Sep 11, 2018 2:22 pm
We missed it in product testing because (dumb luck) our heavy-load testing was done on boards with the other brand of switch, and most of our field testers were only using the board to power mice and keyboards, which works fine on all the HAT/Pi pairs we've tested.
This sort of makes sense, with the exception that I (and others) have reported the over-current warnings being triggered without any device being attached to the USB ports and my initial report of the problem was experienced with just a Logitech wireless keyboard/mouse adaptor, which I'd expect to be fairly low current (though I don't have a USB power tester to measure it).

So in the release to the field, problems were seen even at zero and low load. Just an observation.
Cannot really comment as not part of the investigation, but I suspect there is some variation between different PoE HAT that may explain that. ie some may fail even at the lower loads. We'll be publishing a blog post soon with more details. I can only apologise if this has been a big inconvenience for purchasers. We will be improving our testing procedures to hopefully ensure this doesn't happen again.
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 1:25 pm

martinrowan wrote:
Wed Sep 12, 2018 7:25 am
This sort of makes sense, with the exception that I (and others) have reported the over-current warnings being triggered without any device being attached to the USB ports
I believe the mechanism being described is the USB reservoir caps, on the USB socket side of the limiter, track the supply voltage. When the PoE supply rises or spikes there is an in-rush current into those through the limiter which triggers its over-current warning.

This will likely be worse if there's a negative spike, the reservoir cap voltage drops, before a positive spike.

Fluctuating or noisy supply voltage could also explain the few cases of over-current with no USB devices connected on earlier Pi's.

Behaviour will very much depend on exactly what is connected ( or not ) and it may not always appear to be logically consistent. It depends on how easily the reservoir caps are pulled down or up, how much in-rush there is.

Roken
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 6:42 pm

Except - I see the overvoltage, with literally nothing connected. The one Pi that I have a hat connected to is entirely independent of anything else. All that it relies on is the network. I mean that, inasmuch as even the sdcard does nothing more than boot, and hand over to an NFS boot.

This is, incidentally, why the issue is not currently a problem to me, but for my other PIs will be.
Headless PI. OMG, someone cut it's head off. Oh, hang on. it didn't have one to start with.

shawaj
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 7:44 pm

For anyone who needs a quick fix, here is our PoE HAT (tried and tested for 3+ years) which does not face the same issue and as a plus works with any 40 pin Pi (not just 3B+) - https://uk.pi-supply.com/products/pi-po ... spberry-pi

Will be back in stock in around a week :-)
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weust
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 9:10 pm

That bulky thing on top is the reason I didn't buy yours ;-)
The Raspberry Pi HAT still fits inside a normal case, and doesn't have the ugly passthrough cable.

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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 9:14 pm

shawaj wrote:
Wed Sep 12, 2018 7:44 pm
For anyone who needs a quick fix, here is our PoE HAT (tried and tested for 3+ years) which does not face the same issue and as a plus works with any 40 pin Pi (not just 3B+) - https://uk.pi-supply.com/products/pi-po ... spberry-pi

Will be back in stock in around a week :-)
How can it be 'tried and tested for 3+ years', when the Pi3b+ - the only Pi you can power via POE, has only been out for about half a year?
User experiencing technical difficulties.

piman314
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 9:21 pm

Imperf3kt wrote:
Wed Sep 12, 2018 9:14 pm
How can it be 'tried and tested for 3+ years', when the Pi3b+ - the only Pi you can power via POE, has only been out for about half a year?
Their hat powers other pis, it doesn't rely on the new features of the Pi3B+, so it's not as neat, but it does work, which currently the official hat doesn't. Personally I'll be sticking to the other PoE splitters readily available for now until the RPI team get this slipup sorted out and will get the "fixed" official hat when it's available.

new3pi
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 10:43 pm

This sort of makes sense, with the exception that I (and others) have reported the over-current warnings being triggered without any device being attached to the USB ports and my initial report of the problem was experienced with just a Logitech wireless keyboard/mouse adaptor, which I'd expect to be fairly low current (though I don't have a USB power tester to measure it).

So in the release to the field, problems were seen even at zero and low load. Just an observation.
I'm new to Raspberry Pi but not to computing. I have bought RPi's with POE hats to install Home Assistant to less complicate my server, I'm in the same boat, RPi's are running headless only connected with a powered Ethernet cable, I am also getting 'over-current change' errors on Raspbian making it unworkable. I have overcome this by running the fan using the overlay code as it may be several months before a new hat is released. Disappointed to say the least!

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Imperf3kt
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Re: PoE HAT - USB Ports not working - over-current

Wed Sep 12, 2018 11:46 pm

piman314 wrote:
Wed Sep 12, 2018 9:21 pm
... which currently the official hat doesn't [work]. Personally I'll be sticking to the other PoE splitters readily available for now until the RPI team get this slipup sorted out and will get the "fixed" official hat when it's available.
To me, it sounds more like a problem with the Pi3b+, rather than the POE hat.
I say this because one chip from one vendor works perfect, the same chip from another vendor fails.
User experiencing technical difficulties.

jamesh
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Re: PoE HAT - USB Ports not working - over-current

Thu Sep 13, 2018 8:01 am

Imperf3kt wrote:
Wed Sep 12, 2018 11:46 pm
piman314 wrote:
Wed Sep 12, 2018 9:21 pm
... which currently the official hat doesn't [work]. Personally I'll be sticking to the other PoE splitters readily available for now until the RPI team get this slipup sorted out and will get the "fixed" official hat when it's available.
To me, it sounds more like a problem with the Pi3b+, rather than the POE hat.
I say this because one chip from one vendor works perfect, the same chip from another vendor fails.
No, it's the HAT.

I would expect fixed boards to be available in about a month, but will check.
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drgeoff
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Re: PoE HAT - USB Ports not working - over-current

Thu Sep 13, 2018 8:29 am

Imperf3kt wrote:
Wed Sep 12, 2018 11:46 pm
piman314 wrote:
Wed Sep 12, 2018 9:21 pm
... which currently the official hat doesn't [work]. Personally I'll be sticking to the other PoE splitters readily available for now until the RPI team get this slipup sorted out and will get the "fixed" official hat when it's available.
3

To me, it sounds more like a problem with the Pi3b+, rather than the POE hat.
I say this because one chip from one vendor works perfect, the same chip from another vendor fails.
I disagree. Those large ripple spikes are a bad thing to have on the power rail even if the overcurrent detector is not triggered by them.

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