hippy
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PoE HAT - Usage scenarios

Sun Aug 19, 2018 8:35 am

Is it possible to connect the official PoE HAT to a Pi 3B+ and power the Pi through the micro-USB rather than Power over Ethernet, to allow the PoE HAT to be used purely as a Pi-powered software controlled fan controller ?

Or, to allow a Pi 3B+'s use both when PoE is available and when it isn't.

When the PoE HAT is fitted; is it safe to use PoE while also supplied power via micro-USB or will that cause damage to the Pi etc?

So; will the PoE HAT have to be removed if wanting or needing to power via micro-USB ?

Is it intended that the schematics for the PoE HAT will be published ?

DirkS
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Re: PoE HAT - Usage scenarios

Sun Aug 19, 2018 8:44 am

hippy wrote:
Sun Aug 19, 2018 8:35 am
Is it possible to connect the official PoE HAT to a Pi 3B+ and power the Pi through the micro-USB rather than Power over Ethernet, to allow the PoE HAT to be used purely as a Pi-powered software controlled fan controller ?
£18 for a fan?

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bensimmo
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Re: PoE HAT - Usage scenarios

Sun Aug 19, 2018 11:05 am

DirkS wrote:
Sun Aug 19, 2018 8:44 am
hippy wrote:
Sun Aug 19, 2018 8:35 am
Is it possible to connect the official PoE HAT to a Pi 3B+ and power the Pi through the micro-USB rather than Power over Ethernet, to allow the PoE HAT to be used purely as a Pi-powered software controlled fan controller ?
£18 for a fan?
I think this is more a clarification post. Somebody may want to use it and their PoE setup is down or not yet running and what to plug it in the mains.

hippy
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Re: PoE HAT - Usage scenarios

Sun Aug 19, 2018 12:25 pm

DirkS wrote:
Sun Aug 19, 2018 8:44 am
£18 for a fan?
A speed controlled fan, with speed control already baked into Linux and the firmware. With PoE if one chooses to use it, pre-assembled, tested, with warranty, and with an easy to use HAT fitting, and all the fixtures.

Sure, some people could build the same themselves, but most people wouldn't be able to and many wouldn't want to, not with the challenge of finding a good quality low-profile fan to start with and the faff of programming the HAT EEPROM and a microcontroller to convert I2C control to PWM, plus having to build a PCB to put it on.

Time and effort is money and £18 isn't that expensive for what it is, even if just used as a fan and controller.

Plus, as soon as one adds any home-built contraption to a Pi, and that Pi then fails, the contraption or its assembly will get blamed for that failure. One can think of paying more as buying insurance against "must have been something you did; warranty voided".
bensimmo wrote:
Sun Aug 19, 2018 11:05 am
I think this is more a clarification post. Somebody may want to use it and their PoE setup is down or not yet running and what to plug it in the mains.
That too.

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bensimmo
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Re: PoE HAT - Usage scenarios

Sun Aug 19, 2018 5:11 pm

What is a shame is they didn't use a sensing fan so the speed (and in fact see if it is actually spinning) could be checked.

The ability to check may well have been a bonus to PoE users as they probably cannot see or hear the fan.

There is a reason pretty much every PC/laptop uses sensing fans (and servers?) so they can alert the users of failure.

Anyway back on with the chat.

I think one person who was having problems with them connected up with mains power, so I guess that works.

hippy
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Re: PoE HAT - Usage scenarios

Mon Aug 20, 2018 10:59 am

Some clarification for safe use might also be in order. From -

https://www.raspberrypi.org/products/poe-hat

"Instructions for safe use - To avoid malfunction or damage to your Raspberry Pi product, please observe the following advice: ... Do not expose it to heat from any source; the product is designed for reliable operation at normal room temperatures".

That would seem to be a bit of a conundrum for a product intended to disperse above normal room temperature heat.

ShiftPlusOne
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Re: PoE HAT - Usage scenarios

Mon Aug 20, 2018 11:39 am

hippy wrote: Is it intended that the schematics for the PoE HAT will be published ?
I'm not aware of any plans to do that at this point. Is there any information in particular you're looking for?
hippy wrote: Or, to allow a Pi 3B+'s use both when PoE is available and when it isn't.

When the PoE HAT is fitted; is it safe to use PoE while also supplied power via micro-USB or will that cause damage to the Pi etc?
No issues with having power on both or either end when the HAT is attached.
hippy wrote: Is it possible to connect the official PoE HAT to a Pi 3B+ and power the Pi through the micro-USB rather than Power over Ethernet, to allow the PoE HAT to be used purely as a Pi-powered software controlled fan controller ?
No problem with this either. It could be connected to an older pi to be used as a fan as well. Since older pis run hotter, it's likely the fan will work harder on those models.

hippy
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Re: PoE HAT - Usage scenarios

Mon Aug 20, 2018 12:52 pm

ShiftPlusOne wrote:
Mon Aug 20, 2018 11:39 am
hippy wrote: Is it intended that the schematics for the PoE HAT will be published ?
I'm not aware of any plans to do that at this point. Is there any information in particular you're looking for?
I was really after 'the full power regulation circuit'', but 'the whole lot' would satisfy my curiosity.

I was speculating whether the HAT could be used to provide PoE for Pi boards other than the 3B+, even other products. That would obviously require additional hardware, an additional ethernet jack from which PoE could be extracted at least, and perhaps modifications to the board, but that might be worth it to some.

I was also wondering if it could be used as a step-down regulator for non-5V supplies, what it's operating envelope would be, what limitations there were, whether it could be modified for that use.

Obviously knowing what the actual circuitry is and components used would help answer those questions.

I was hoping the full schematic would be published to save having to purchase a board and reverse engineer it myself, or having to wait for someone else to do that. I would rather have an official schematic than something from a third-party, and would prefer not to have to do the reverse engineering myself.

Many thanks for the other clarifications. One question I hadn't asked ...

If power is supplied over PoE and through the micro-USB; which does the Pi use for its power ?

How the HAT handles voltage mis-matches and prevents damaging an incoming micro-USB supply when both are connected is one thing which intrigues me. The 3B had the 'ideal diode' Q3 but the 3B+ doesn't. Having the circuit diagram could answer that. I'm happy to take a written explanation though.

ShiftPlusOne
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Re: PoE HAT - Usage scenarios

Mon Aug 20, 2018 1:15 pm

I'll have to leave those ones to the hardware folk, since it's mostly black magic to me.

hippy
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Re: PoE HAT - Usage scenarios

Mon Aug 20, 2018 1:27 pm

ShiftPlusOne wrote:
Mon Aug 20, 2018 1:15 pm
I'll have to leave those ones to the hardware folk, since it's mostly black magic to me.
No problem.

You might want to get the Trademark Team to cast their eyes over this ...

https://www.tindie.com/products/canerdu ... i3-model-b

The description "Power Over Ethernet HAT for Raspberry Pi3 Model B+" may be okay but silk-screening the board "RaspberryPi 3 B+ POE HAT" possibly breaches usage guidelines.

I was searching for a photo of the rear of the official PoE HAT board when I came across that. If the RPT/RPF or anyone could put one on-line that would be useful.

Found one - https://www.rasppishop.de/media/image/p ... l-b-~2.jpg

And another question. I guess a JST/whatever connector be added to the unused pads which are marked "5V out" on the top side of the board ? Does that void warranty if one does ?

ShiftPlusOne
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Re: PoE HAT - Usage scenarios

Mon Aug 20, 2018 2:53 pm

hippy wrote:
Mon Aug 20, 2018 1:27 pm
You might want to get the Trademark Team to cast their eyes over this ...
Thanks, I've forwarded it on.

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bensimmo
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Re: PoE HAT - Usage scenarios

Mon Aug 20, 2018 4:57 pm

Thanks for the rear view picture link.

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