Question [SOLVED] Basic LAN/PoE type question.

[chuffedas]

I am new to playing with a LAN. Also new to PoE.
I picked up a NetgearGS110TP V3. Well, it has a 400 page manual
I am using it to power a CM4 PoE board. I have also used it to run a Pi4 using an ethernet splitter.
I tried to use it for my desktop Pi5, but realised I need something that can cope with more power.

So, as I understand it, it 'knows' whether something is PoE or not. Because it 'asks' it, right?

So, I get that my PC will have no problem telling the switch that it doesn't want PoE, too big.
BUT, currently, I am powering my Pi5 with mains adapter, I just want to make sure I am thinking this right.
I can leave it powered by mains and use the switch to just provide data. My thinking is that the Pi5 can be run by PoE, but it needs a board, so does the Pi5 say that it doesn't want PoEand to only send data, and it would be the PoE board that tells the switch that it wants Power as well? I suppose I am confused because I know the Pi5 CAN be PoE, how does the switch know it doesn't want PoE at this time?
I just trust the switch to know the right thing to do?

Can I trust it with all devices? Or are there some that don't work with it and will fry?
I also have a CM3 carrier board that is audio orientated which is powered separately and I would want it to just be data only.

Thanks.

 

[kanewolf]

I am new to playing with a LAN. Also new to PoE.
I picked up a NetgearGS110TP V3. Well, it has a 400 page manual
I am using it to power a CM4 PoE board. I have also used it to run a Pi4 using an ethernet splitter.
I tried to use it for my desktop Pi5, but realised I need something that can cope with more power.

So, as I understand it, it 'knows' whether something is PoE or not. Because it 'asks' it, right?

So, I get that my PC will have no problem telling the switch that it doesn't want PoE, too big.
BUT, currently, I am powering my Pi5 with mains adapter, I just want to make sure I am thinking this right.
I can leave it powered by mains and use the switch to just provide data. My thinking is that the Pi5 can be run by PoE, but it needs a board, so does the Pi5 say that it doesn't want PoEand to only send data, and it would be the PoE board that tells the switch that it wants Power as well? I suppose I am confused because I know the Pi5 CAN be PoE, how does the switch know it doesn't want PoE at this time?
I just trust the switch to know the right thing to do?

Can I trust it with all devices? Or are there some that don't work with it and will fry?
I also have a CM3 carrier board that is audio orientated which is powered separately and I would want it to just be data only.

Thanks.

There are (unfortunately) multiple versions of power over ethernet. Your switch is "PoE+" -- there is a standard for that IEEE802. 3at. You can supply up to 30W on an ethernet port with POE+. With a proper USB-C adapter or POE HAT, you should be able to power your PI5.
There is a handshake that happens on the port for the device to have power provided. Plugging a non-POE device into a POE port is safe. If you desire more security you can disable POE on a per-port basis in the web based GUI for the switch. See page 95 in the users manual -- https://www.downloads.netgear.com/files/GDC/GS108Tv3/GS108Tv3_GS110TPv3_GS110TPP_UM_EN.pdf

 

[lantis3]

You need an add-on board to power Pi 5

https://www.amazon.com/s?k=Power+Over+Ethernet+HAT+(F)+Compatible+with+Raspberry+Pi+5

 

[chuffedas]

Wow, wonderful help, thank you very much.
Yes, I intend to PoE my Pi5 with a hat or better adapter.
I think I will disable the POE, as you say, a bit more peace of mind. I hadn't thought that might be a thing.
My concern was that, because the Pi5 is POE-able, it IS a POE device, I just don't want it to be right now.
Or, is the Pi5 NOT a POE device when it is stand alone, but the hat that you attach to it is the POE device that the switch recognises?
Incredibly nice of you to look up the page for me as well, I really appreciate that.

 

[chuffedas]

You need an add-on board for Pi 5

https://www.amazon.com/s?k=Power+Over+EtherWith the Pi5, I idenet+HAT+(F)+Compatible+with+Raspberry+Pi+5

Yes, thank you.
I need to be having a bit of a think of what to do re the poe side of things.
This is just an 'in the mean time' sort of thing while I work things out a bit.
I want to free up a socket on my router as I want to run an ethernet extension to upstairs.

Just an a bit of an explanation, I want to build a vertical (So that it can slide behind a unit nicely out of sight) wooden board/case and ideally silent (preferably passive) cooling. Probably with a back up Noctua fan at the top with the case funneling the air directly over the heatsiink. So I might be using the Poe hat via jumpers. I also have a CM4 POE board that i use as my PVR.
I am also throwing into the mix that I want to make a better DAC and Amp for the PVR and Pi5.
I am needing to take each step at a time.
Learning stuff though, which is fun.

 

[kanewolf]

Wow, wonderful help, thank you very much.
Yes, I intend to PoE my Pi5 with a hat or better adapter.
I think I will disable the POE, as you say, a bit more peace of mind. I hadn't thought that might be a thing.
My concern was that, because the Pi5 is POE-able, it IS a POE device, I just don't want it to be right now.
Or, is the Pi5 NOT a POE device when it is stand alone, but the hat that you attach to it is the POE device that the switch recognises?
Incredibly nice of you to look up the page for me as well, I really appreciate that.

The PI5 is not a POE device without the POE HAT.

 

[chuffedas]

The PI5 is not a POE device without the POE HAT.

Perfect, thank you so much for your help.
It now makes more sense in my head.
Plugged it into switch (slight breath hold while I did it I have to admit, lol).

 

[bill001g]

802.3ax/at is a active form of PoE. A device that uses this form of PoE must request the amount of power it wants by telling the switch how many watts or class it wants. The switch know how much total power budget it has so it know the total amount of power it can deliver to all the PoE connected devices. So a device might actually be told no if other devices already used it up.

The part I am not sure of is since this is active protocol how does the end device get enough power to even be able to request the needed power. Kinda the chicken and egg issue it has to have power to request power.

I think the switch constantly puts out a very low voltage low amp power all the time. It is not enough to damage non poe equipment but enough to boot the poe ethernet chip in the end device. Only after the device request the power does it switch to 48 volts. It is this high voltage that would damage non poe equipment but it never puts it out until it is requested. The 48 volts though is what allows it to deliever a lot of power at the full 100 meter ethernet cable limit.

What is called passive PoE puts out power constantly. This is all non standard proprietary stuff. In many cases it is fairly low voltage like 5-12 volts. Although there is no guarantee this should not hurt non poe devices. Some 24 volts systems you ahve to be very careful with. What tends to be the largest issue with a lot of forms of this non standard poe is the port only run 100mbps because unlike the standard 802.3 form of poe they may not transfer data and power over the same pairs of wires.


So if you are still awake the short answer is your switch is smart enough to not put power out to devices that can not use it.

 

[chuffedas]

802.3ax/at is a active form of PoE. A device that uses this form of PoE must request the amount of power it wants by telling the switch how many watts or class it wants. The switch know how much total power budget it has so it know the total amount of power it can deliver to all the PoE connected devices. So a device might actually be told no if other devices already used it up.

The part I am not sure of is since this is active protocol how does the end device get enough power to even be able to request the needed power. Kinda the chicken and egg issue it has to have power to request power.

I think the switch constantly puts out a very low voltage low amp power all the time. It is not enough to damage non poe equipment but enough to boot the poe ethernet chip in the end device. Only after the device request the power does it switch to 48 volts. It is this high voltage that would damage non poe equipment but it never puts it out until it is requested. The 48 volts though is what allows it to deliever a lot of power at the full 100 meter ethernet cable limit.

What is called passive PoE puts out power constantly. This is all non standard proprietary stuff. In many cases it is fairly low voltage like 5-12 volts. Although there is no guarantee this should not hurt non poe devices. Some 24 volts systems you ahve to be very careful with. What tends to be the largest issue with a lot of forms of this non standard poe is the port only run 100mbps because unlike the standard 802.3 form of poe they may not transfer data and power over the same pairs of wires.


So if you are still awake the short answer is your switch is smart enough to not put power out to devices that can not use it.

Interesting stuff. Thank you for this.
That all makes sense.