POE hat

[pyromaniac511]

I'm having a 3u, 12 pi rack mount 3d printed and wanted to use POE hats but am unsure which to get. The official is like 50% more than the rest, is that the normal go to or do yall have good experiences with other brands? I'll be powering with a Cisco 3560 or 3750 switch.

[ejolson]

I'm having a 3u, 12 pi rack mount 3d printed and wanted to use POE hats but am unsure which to get. The official is like 50% more than the rest, is that the normal go to or do yall have good experiences with other brands? I'll be powering with a Cisco 3560 or 3750 switch.

I've heard of some third-party POE hats that destroyed the Pi and others that worked. I can't remember details nor find the posts. It should be possible to connect some jumper wires to test one before connecting the side which delivers 5V to the GPIO connector.

I took a different approach to my 12 Pi in a 2U space and simply used an ATX supply with a sturdy 5V power rail. Note that only very old supplies have 5V in excess of 40 amperes. Details and photographs are available at

viewtopic.php?f=36&t=272660

[6by9]

Also check whether the third party ones support gigabit ethernet or only 100Mbit/s. The Pi PoE HAT supports gigabit.

[pyromaniac511]

I do have some old server PSU's. I'll look into them to see what they are rated for. POE is cleaner looking but at 20-30 a card, I think I can overlook a few wires.

[ejolson]

I do have some old server PSU's. I'll look into them to see what they are rated for. POE is cleaner looking but at 20-30 a card, I think I can overlook a few wires.

Since POE also allows individual power cycling of individual ports (assuming a reasonable switch), the ATX approach requires a separate way to reset a Pi that may have locked up or joined a botnet by accident. My solution was to run a wire from the GPIO of an additional controller Pi to the run pins on each of the Pi's that form the cluster. For economy, I chose a Pi Zero to be the run enable controller, but another 4B would have worked as well.

[ejolson]

In my 2U case, since I am using USB-C to deliver power to the Pi 4B, I decided I might as well leverage the data lines on that cable as well. The result is that each Pi has two network connections: Gigabit Ethernet plus a USB network gadget.

Using a separate lower-speed network for system monitoring and management is common in clouds and clusters. I've verified both connections work but am still planning the software configuration.

[pyromaniac511]

The result is that each Pi has two network connections: Gigabit Ethernet plus a USB network gadget.

This intrigues me, what is the other end of the USB-C connected too? I haven't seen USB hubs that could handle 3a and my assumption that USB power stations don't do data. This is very much along the lines of what we do with our network for monitoring/controlling . Would you mind explaining your set up in more detail or provide a link that you leaned from please.

[plugwash]

Also check whether the third party ones support gigabit ethernet or only 100Mbit/s. The Pi PoE HAT supports gigabit.

I'd expect any HAT that used the 4-pin PoE header to work with gigabit.

A bigger concern I have is that some of the third part PoE hats do not seem to be isolated. If there are faults on the Ethernet wiring of if the maker of the power sourcing equipment also ignores the isolation requirements of the PoE spec then this could lead to unwanted voltages on the Pi's ground which depending on what other equipment is connected to the Pi could lead to damage.

48 volts is reasonably safe for humans in dry conditions but it is a significant threat to microelectronics.

It's usually fairly easy to tell the difference visually between an isolated and a non-isolated converter. All switchmode converters contain at least one (and for simple converters usually exactly one) inductive element. In a non-isolated converter the inductive element will be a simple inductor.in an isolated converter it will be a transformer.

[ejolson]

The result is that each Pi has two network connections: Gigabit Ethernet plus a USB network gadget.

This intrigues me, what is the other end of the USB-C connected too? I haven't seen USB hubs that could handle 3a and my assumption that USB power stations don't do data. This is very much along the lines of what we do with our network for monitoring/controlling . Would you mind explaining your set up in more detail or provide a link that you leaned from please.

The hubs are connected to internal USB headers of an mATX PC motherboard.

I sort of made the hubs myself: Not the way a cook makes food from scratch but more like someone in quarantine adding rolled oats to a brownie mix and calling the result a breakfast bar.

Specifically, I pried apart an unpowered USB2 hub, cut and lifted the 5V power pin from the sockets with a razor blade, soldered the lifted pins to a length of 18 guage wire, connected the wire to an automotive fuse of suitable amperage and that to the 40 amp 5V rail of the ATX supply. I ran an additional ground wire for good luck, but did not cut anything because ground is common inside the server chassis.

Everything would have gone well except the first hub I ruined by opening it with a saw before I learned how to pry them apart. There was also that late-night stupidity where I wired the third and fourth hubs backwards.

In all, the hubs were cheap and the 5V modifications not difficult. However, if I were filling a rack and needed to modify 100 of them, the price of a POE hat would start to look pretty attractive.

[6by9]

Also check whether the third party ones support gigabit ethernet or only 100Mbit/s. The Pi PoE HAT supports gigabit.

I'd expect any HAT that used the 4-pin PoE header to work with gigabit.

A large number of the PoE solutions I've seen do NOT use the 4-pin header, and have loop through RJ45 connectors. eg https://uk.pi-supply.com/products/pi-po ... spberry-pi or https://www.amazon.co.uk/DSLRKIT-Active ... B01H37XQP8 (although there's a near identical one which does do gigabit https://www.amazon.co.uk/dp/B074Y6M67F/ref=dp_cerb_2)
There is no guarantee that these work with gigabit, so read the specs carefully, and buyer beware.

[ejolson]

I've heard of some third-party POE hats that destroyed the Pi and others that worked. I can't remember details nor find the posts. It should be possible to connect some jumper wires to test one before connecting the side which delivers 5V to the GPIO connector.

The thread on POE hats that might have caused problems is

viewtopic.php?t=272698

The fact that I wanted to include an x86 file server inside the same 2U chassis led me to the hardware that I'm currently working with. In my opinion, being able to remotely power cycle and reset an individual Pi is important when they are rack mounted, even if not collocated at a high-security data center. Speaking of which, I now have a quote for a half rack at the Switch Citadel. This means

• The minimum deployment there would be eight to ten 2U servers.
• Given a density of 24 Pi per box, I would need 48 to 60 modified hubs.

Most likely my socially-distanced face-mask-wearing teaching job will restart before then. Truthfully, I'm more than a little concerned what will happen in a room of college students with bandanas over their faces. One of my colleagues--an expert in the spread of epidemics--said he thinks reclosing operations due to a breakout is a matter of when not if.

In my opinion, an official standard and certification process what constitutes a face mask for socially distancing would be as useful as a similar certification program for the quality and compatibility of third-party POE hats.

[ejolson]

This intrigues me, what is the other end of the USB-C connected too?

I just posted an annotated photograph of the hardware setup at

viewtopic.php?p=1695936#p1695936

I'll be fleshing out the software side of things in the same thread soon.

[pyromaniac511]

Thats pretty sweet, I hope I see your post whenever you make it.

[ejolson]

Thats pretty sweet, I hope I see your post whenever you make it.

The hardware is up and running now for a couple weeks. It seems pretty stable. Right now I'm now tidying up the configuration scripts for creating the boot images and trying decide whether I want to include an additional option to create root filesystems which are not encrypted. In the crazy security direction I'm also thinking about enabling Dropbear ssh for the initial RAM filesystem in case a person wants to store the secret keys offline.

It's curioius that we both ended up with twelve Pi 4B computers. Do you have a particular application in mind for your cluster?

[pyromaniac511]

It's curioius that we both ended up with twelve Pi 4B computers. Do you have a particular application in mind for your cluster?

I'm working with a bunch of kids on stem stuff and got tired of having a pile of pies lying around with a crap load of power bricks and daisy chaining power strips. I found a rack on thingaverse and had a local person 3D print it for me. It had 12 slots so 12 is my magic number I guess.

I would like to look into making a cluster as a web server or something just because . We will be getting into web development so a cluster might be easier to manage than individual pies (although 1 is probably way more than enough for 10-30 kids and nearly no visitor traffic)... ok ok, I just want to make a rack with cool lights an stuff

[ejolson]

It's curioius that we both ended up with twelve Pi 4B computers. Do you have a particular application in mind for your cluster?

I'm working with a bunch of kids on stem stuff and got tired of having a pile of pies lying around with a crap load of power bricks and daisy chaining power strips. I found a rack on thingaverse and had a local person 3D print it for me. It had 12 slots so 12 is my magic number I guess.

I would like to look into making a cluster as a web server or something just because . We will be getting into web development so a cluster might be easier to manage than individual pies (although 1 is probably way more than enough for 10-30 kids and nearly no visitor traffic)... ok ok, I just want to make a rack with cool lights an stuff

Are you planning to connect monitors and keyboards to the Pi computers or will the children in the STEM group access them some other way?

[andydavies]

I'm having a 3u, 12 pi rack mount 3d printed and wanted to use POE hats but am unsure which to get. The official is like 50% more than the rest, is that the normal go to or do yall have good experiences with other brands? I'll be powering with a Cisco 3560 or 3750 switch.

I've just ordered a few of the WaveShare POE hats to try - https://www.waveshare.com/wiki/PoE_HAT_(B) - as I'm rather disappointed by the official PoE HAT

The coil on the official PoE HAT whistles when the Pi is powered off, and the fan is woefully small so it's noisy