Racks and Power Supplies

Hello EmsTatay!

11 Feb 19 10:18, you wrote to Rick Christian:

An elegant solution, I found the horror stories to be true.

That works o.k. but it moves the warts to the vincinity of the RPI. Ethernet speeds are limited to 100Mhz, as the four extra wires are not passed from one side of the splitter to the other.

There could be models, that do.

I did.

Who knows.

Kees

Hi Rick, reading your requirements and wish to eradicate he pesky warts from your life... My first thought was to use R-Pi PoE HAT. However, seems that there is a problem with their function and AFAIK they have been recalled/put on hold. A practical (and may be even cheaper) alternative to the HAT would be to use a PoE splitter with a 5V 2.4A supply (4 pack on amazon < CAD 10 ea). Use the already existing Cat5 cabling, add a suitable PoE supply unit and hook up as many of your Pi's as the PoE adapter allows.

Haven't tried it myself - but that might be one way to solve what you would like to achieve.

Greets/J

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PS: In Case you are into 3D printing or willing to try that (from your own description you are not into HW/building - I know...) There is a nifty design of a 2-3U rack for up to 14 Pi's which may take

30+ hours to print but would be providing you with a rack mount (add the PoE Gigbabit Switch and the PoE splitters and you are done...

I would likely re-design the design posted on thingiverse - but it seems a good starting point...

Greets/J

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Hi Kees!

Thanks for your thoughts. In this setup there would be only ONE Power Supply feeding the PoE Switch (that was the request/wish/idea of the OP)

The splitter I mentioned above eliminates the problem with the HAT... Whilst the splitter will use the extra wires for the PoE function, my PI-2 and PI-3 are limited to 100Mb/s (NOT MHz ;-) - so not a problem or performance limit.

According to 802.3af the data function of the wire AND PoE fucntion "can" coexist. Thus you need a G-Bit Switch with PoE function and if your (future) PI supports G-bit ... the splitter needs to do the same.

I agree that the < CAD 40 4 pack I linked does NOT specify Gigabit compliance and likely only supports 100Mb/s- However, THE following model DOES support G-bit (please note I am not a seller or affiliated with any of the product):

(of course this one is $15 (US) ... I am sure it can be found for a better price...

It should be noted that the Switch must support the power requirements of the number of R-PI's you will connect. It is noteworthy that PoE input is around 48V and would be stepped down by the splitter to provide the 5VDC for the PI.

I think this would be a viable/stable setup. (Only ONE reviewer reports undervoltage on his PI(s) and I suspect that this is likely due to his sizing of the PoE supply rather than the splitter. )

Greets/J

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Hello EmsTatay!

11 Feb 19 16:22, you wrote to me:

Em> Thanks for your thoughts. In this setup there would be only ONE Power Em> Supply feeding the PoE Switch (that was the request/wish/idea of the OP)

Yes, that is also the attraction to me.

Em> The splitter I mentioned above eliminates the problem with the HAT... Em> Whilst the splitter will use the extra wires for the PoE function, my Em> PI-2 and PI-3 are limited to 100Mb/s (NOT MHz ;-) - so not a problem or Em> performance limit.

The POE-Pihat, seems to be limited to 100Mb/s as well. Strange, as it is meant for the Pi3+ wich has a Gb/s interface. It is still limited to USB2 speeds.

Em> According to 802.3af the data function of the wire AND PoE fucntion Em> "can" coexist. Thus you need a G-Bit Switch with PoE function and if Em> your (future) PI supports G-bit ... the splitter needs to do the same.

I use a Netgear Prosafe GS108PE, it supprts POE only on 4 ports. All 8 ports are 1Gb/s.

Em> I agree that the < CAD 40 4 pack I linked does NOT specify Gigabit Em> compliance and likely only supports 100Mb/s- However, THE following Em> model DOES support G-bit (please note I am not a seller or affiliated Em> with any of the product):

Em>

Em> 1 4C

Interestign, up till now I only searced local suppliers and found no splitters with support for 1Gb/s

Em> (of course this one is $15 (US) ... I am sure it can be found for a Em> better price...

Possibly.

Em> I think this would be a viable/stable setup. (Only ONE reviewer reports Em> undervoltage on his PI(s) and I suspect that this is likely due to his Em> sizing of the PoE supply rather than the splitter. )

I only encoundered undervoltage with the Pi-hat POE. I am not sure if it is a version v1 or v2.

Kees

Have you a ref for the 100M restriction? I've done a bit of googling and not found anything that says that for the official pi 3+ poe hat.

Then again I've not found anything that explicitly says it does work at gigabit!

I think it comes with the af-2003 spec. Newer "at-20something" makes gigabit possible.

Hello Jim!

12 Feb 19 19:28, you wrote to me:

JJ> Then again I've not found anything that explicitly says it does work at JJ> gigabit!

No, wrong conclusion from my side. I found a remark to limit the speed speed of the Pi3+ to 100Mb/s if there were problems with connecting. I remember that to be in relation with the pi POE-Hat. As usual when you read something on the web, you cannot find it again.

But anyhow, there is no circuit reason why the POE-Hat could influnece the maximum speed of the ether net port on the Rpi3+ as it is not an in-between-device tah can limit the number of available wires on the ethernet cable.

Anyway here is the real answer to the issues:

Sorry for the possible confusion.

Kees