Zilch0
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Re: A DIY PoE solution

Sun Feb 12, 2012 7:38 pm

To start off: I assume no responsibility what-so-ever, of what might result of following any advice in the text below!

I've been thinking about the PoE thingy, and remember years ago trying to set up LAN over a phone cable ( RJ11 ) and remember it actually working! I did expect a speed loss, tough. So I thought, could I actually use some of the wires inside a normal network cable to send power to RasPI?

Well the answer is YES!

Some googling around and - voila!

http://tech2.in.com/how-to/wif.....ter/223062

Now actually 100BASE-TX (100mb nominal speed network) uses only two pairs, so you wont even get a speed penalty! Four pairs is only needed for a gigabit network, but RasPI doesn't suppor that, for now.

[Re]sources

http://en.wikipedia.org/wiki/E.....isted_pair [section Variants]

http://en.wikipedia.org/wiki/1.....100BASE-TX [section 100BASE-TX]

"Like 10BASE-T the active pairs in a standard connection are terminated on pins 1, 2, 3 and 6." The table with colors tells us that we got blue, white/blue, brown and white/brown available for power (or any other use).

Have a nice pi,

Mika

Zilch0
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Re: A DIY PoE solution

Sun Feb 12, 2012 7:48 pm

Here's a much nicer application, the theory is still the same:

http://www.instructables.com/i.....r-For-Rou/

Mika

Lynbarn
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Re: A DIY PoE solution

Sun Feb 12, 2012 8:10 pm

If you don't want to make your own, there is also THIS available, and it's only about a fiver.

plugwash
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Re: A DIY PoE solution

Sun Feb 12, 2012 11:31 pm

Lynbarn said:


If you don't want to make your own, there is also THIS available, and it's only about a fiver.


And doesn't have the right connector for the pi. Selling that as a Pi accessory is seriously stretching the truth (they admit you will need an adaptor but say they are still looking for one.....) If you are going to have to cut up the adaptors to splice in a USB cable you may as well just cut up the network cable and splice in a USB cable.

But there is a bigger issue with running the Pi directly off a ghetto POE* system. The Pi is intended for a regulated 5V supply and this means you are likely to have volt drop problems running it though a long cable.

According to wikipedia cat5 is 24AWG and 24AWG wire has a resistance of 84.22 milliohms per meter. In a typical ghetto POE setup you would use two cores for positive and two cores for negative. So the resistance in the positive line will be 42.11 milliohms per meter and the resistance in the negative line will also be 42.11 milliohms per meter. That means at a load of 1A you would be losing 84.22 millivolts for every meter of cable. Doesn't sound like much but it means by 10m you will have lost 0.844 volts. At 20m you will have lost 1.688 volts. I dunno how low the Pis 5V line can go before things start to flake out but I wouldn't reccomend a 5V ghetto POE system for anything more than a few meters.

If you do want to power the Pi using a "ghetto POE" system over long runs then my advice would be to run 24V down the ethernet cable and use a DC-DC converter module to power the Pi. With a 24V PSU and a wide input DC-DC converter (e.g. http://uk.farnell.com/powerpax...../2060987  and http://uk.farnell.com/tracopow.....dp/1696320 ) you should be able to do 100m (the limit of normal twisted pair ethernet) easily.

* That is a system that runs power down an ethernet cable but does not implement IEEE standard POE.

Docteh
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Re: A DIY PoE solution

Mon Feb 13, 2012 4:49 am

I also assume no responsibility for anything.

My thoughts on PoE:

The Proper standard stuff with the negotiation (802.af ?) is da bomb. If you plug a laptop in somewhere it shouldn't be, you don't fry an ethernet adaptor. Keep other people away from your PoE stuff.

Don't apply a higher voltage eg 6 or 7 to a line to make up for line losses. That whole v=ir equation is for a specific load level, change it and you end up changing the voltage. Also doing this would prevent you from taking the whole rig inside and running it off of a 3 foot ethernet cord for bench testing.

Short circuit protection is a really really good thing. PacWireless/Laird makes PoE injectors that have this, the light goes off or blinks at you when you short circuit the power pins. Or maybe use some properly sized fuses. 1amp of power at 24 volts should give you around 4 amps of 5volt power after line loses and inefficiency.

Most people doing PoE non standard, standardized on using pins 4,5 (blue pair) as positive, and the brown pair as negative.

For ethernet over untwisted wires, don't do it. Ethernet doesn't handle signal problems with any sort of grace. Forcing one side to talk at 10mbps is the only thing you can do in that case. The link will work, or it won't. If the interference is making it between working and not working you'll have a heck of a time posting on the forums asking for help

stormy1
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Re: A DIY PoE solution

Mon Feb 13, 2012 5:20 am

I will be making one of these for my own use.

6ft total power cable length is the max for 5V.

This includes any wire to the adapter and from the Ethernet cable to the PI power connector.

Anything over 6 feet as stated above use 12V and a switching voltage regulator.

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cnxsoft
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Re: A DIY PoE solution

Mon Feb 13, 2012 8:55 am

Maybe I don't understand what you are trying to do.

If you want to power your board with PoE, I understand you'd have to make some kind of RJ-45 to micro-USB cable.

stormy1
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Re: A DIY PoE solution

Mon Feb 13, 2012 5:41 pm

cnxsoft said:


Maybe I don't understand what you are trying to do.

If you want to power your board with PoE, I understand you'd have to make some kind of RJ-45 to micro-USB cable.


yes that is exactly what I plan on doing.

crimp 4 wires from a cat5 or higher cable into rj45 ends and solder the other 4 to a micro-usb connector on one end and a usb A connector on the other. (bought a 1 foot mircro-usb cable that I will cut in half)

stormy1
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Re: A DIY PoE solution

Mon Feb 13, 2012 5:46 pm

If you dont want to solder you can user a cat5 box like this one.

http://www.monoprice.com/produ.....8;format=2

Or a keystone jack like this one depending:

http://www.monoprice.com/produ.....8;format=2

pjac
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Re: A DIY PoE solution

Wed Oct 03, 2012 1:06 pm

plugwash wrote:But there is a bigger issue with running the Pi directly off a ghetto POE* system. The Pi is intended for a regulated 5V supply and this means you are likely to have volt drop problems running it though a long cable. ... I dunno how low the Pis 5V line can go before things start to flake out but I wouldn't reccomend a 5V ghetto POE system for anything more than a few meters.

If you do want to power the Pi using a "ghetto POE" system over long runs then my advice would be to run 24V down the ethernet cable and use a DC-DC converter module to power the Pi. With a 24V PSU and a wide input DC-DC converter (e.g. http://uk.farnell.com/powerpax...../2060987  and http://uk.farnell.com/tracopow.....dp/1696320 ) you should be able to do 100m (the limit of normal twisted pair ethernet) easily.

* That is a system that runs power down an ethernet cable but does not implement IEEE standard POE.
Having tried this, your advice was spot on :)

The 24V DC step-down approach worked for passive POE at 40m, exceeding my previous limit of 30m passive POE (using up to 12.2V, with or without a step-down). Links are to my blog.
Last edited by pjac on Thu Apr 17, 2014 10:08 am, edited 2 times in total.

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malakai
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Re: A DIY PoE solution

Wed Oct 03, 2012 1:17 pm

Your project is so nice are you planning on doing any tutorials on astronomy with the Pi I just saw what others are doing by putting the camera's into telescopes astonishing. Would love to get into the hobby but need advice on where and how people are doing this especially with the Pi.
http://www.raspians.com - always looking for content feel free to ask to have it posted. Or sign up and message me to become a contributor to the site. Raspians is not affiliated with the Raspberry Pi Foundation. (RPi's + You = Raspians)

pjac
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Re: A DIY PoE solution

Wed Oct 03, 2012 2:39 pm

malakai wrote:Your project is so nice are you planning on doing any tutorials on astronomy with the Pi I just saw what others are doing by putting the camera's into telescopes astonishing. Would love to get into the hobby but need advice on where and how people are doing this especially with the Pi.
I've not actually tried combining my Raspberry Pi with my telescope yet (I've only used the telescope with a laptop). That's probably off topic for this thread though.

My Raspberry Pi with power-over-ethernet was for another project (monitoring a webcam in a birdbox).

TheNthDr
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Re: A DIY PoE solution

Tue Nov 13, 2012 1:53 am

pjac wrote:
malakai wrote:Your project is so nice are you planning on doing any tutorials on astronomy with the Pi I just saw what others are doing by putting the camera's into telescopes astonishing. Would love to get into the hobby but need advice on where and how people are doing this especially with the Pi.
I've not actually tried combining my Raspberry Pi with my telescope yet (I've only used the telescope with a laptop). That's probably off topic for this thread though.

My Raspberry Pi with power-over-ethernet was for another project (monitoring a webcam in a birdbox).
Hi there malakai
i did a search for astronomy related posts and yours caught my eye , might be off topic here but i have an idea for a project hopefully using the Pi to power a lifecam for my scope

have you had any luck in this area yet

TheNthDr

plugwash
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Re: A DIY PoE solution

Thu Nov 15, 2012 2:27 am

cnxsoft wrote:If you want to power your board with PoE, I understand you'd have to make some kind of RJ-45 to micro-USB cable.
As I already said it's not that simple unless your distance requirements are very low. Whatever you do you need a soloution that can deliver damn near 5V to the Pi despite varying loads.

Basically there are four main possibilities

1: True PoE, this is the least risky soloution because it's got a load of protection systems built in but it requires relatively complex (and therefore relatively expensive) hardware at both ends to inject the power and to extract and convert it.
2: 5V ghetto PoE, this sounds like a good idea at first but due to cable resistance it simply will not work properly over nontrivial cable lengths. The voltage drop will just be too much.
3: 12V ghetto PoE with a switched mode converter (you DO NOT want to try and use a linear regular, it will waste a lot of power and get bloody hot) at the Pi end. With the right DC-DC converter and all wires used in the cable it should be possible to get up to 50-60M with such a setup. I wonder why the astronomy guy failed, my guess is his ebay adaptors were using using two wires rather than four.
4: 24V ghetto PoE with a step down converter at the Pi end. This should work fine out to the 100M maximum distance of ethernet (and probablly beyond), main downside is that you will likely have to buy the 24V PSU specifically (whereas a 12V PSU you are likely to have lying around).

I also notice the astronomy guy tried to use higher voltages to compensate for cable loss without using a DC-DC converter. I strongly reccomend against this practice because it will make the voltage delivered to the Pi swing wildly depending on what is currently drawing current and carries a high risk of damaging the Pi.

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TWAWLW
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Re: A DIY PoE solution

Tue Nov 20, 2012 8:25 am

I have just found another POE Injector/Splitter for less than a pound:

http://cgi.ebay.de/ws/eBayISAPI.dll?Vie ... 3071196698

What do you think of this?

plugwash
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Re: A DIY PoE solution

Tue Nov 20, 2012 11:41 am

With adaptors like that you don't know how they are wired. In particular you don't know if they have used all four spare wires or only two of them. Personally i'd much rather splice things into the ethernet cable myself so I knew exactly how they were wired and potentially also to remove the risk of misconnection by avoiding taking power through ethernet connectors that could be plugged into other devices.

Also as I have said many times passive adaptors alone will be pretty useless for running the Pi. You need a higher voltage supply at the source and a DC-DC converter at the Pi for reliable operation over any significant cable length (and if it's only a meter or two why bother running over an ethernet cable at all).

pjac
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Re: A DIY PoE solution

Tue Jan 01, 2013 1:08 am

plugwash wrote:Basically there are four main possibilities

1: True PoE, this is the least risky soloution because it's got a load of protection systems built in but it requires relatively complex (and therefore relatively expensive) hardware at both ends to inject the power and to extract and convert it.
Not tried that.
plugwash wrote:2: 5V ghetto PoE, this sounds like a good idea at first but due to cable resistance it simply will not work properly over nontrivial cable lengths. The voltage drop will just be too much.
Yep, works fine for modest cable lengths (blog post).
plugwash wrote:3: 12V ghetto PoE with a switched mode converter (you DO NOT want to try and use a linear regular, it will waste a lot of power and get bloody hot) at the Pi end. With the right DC-DC converter and all wires used in the cable it should be possible to get up to 50-60M with such a setup. I wonder why the astronomy guy failed, my guess is his ebay adaptors were using using two wires rather than four.
I assume by astronomy guy you mean me, and yes, even with 12V and a DC-DC convert I only got this to work at 30m not 40m (blog post). Your hunch about the passive PoE adaptors not using as many wires as possibly is intriguing.
plugwash wrote:4: 24V ghetto PoE with a step down converter at the Pi end. This should work fine out to the 100M maximum distance of ethernet (and probablly beyond), main downside is that you will likely have to buy the 24V PSU specifically (whereas a 12V PSU you are likely to have lying around).
This has worked for me at 40m (I don't currently have a longer ethernet cable or need to try any longer distances) (24V PoE blog post).
plugwash wrote:I also notice the astronomy guy tried to use higher voltages to compensate for cable loss without using a DC-DC converter. I strongly reccomend against this practice because it will make the voltage delivered to the Pi swing wildly depending on what is currently drawing current and carries a high risk of damaging the Pi.
Again I presume that was me you were talking about - that was a one off experiment (blog post), and I was monitoring the voltage at the Raspberry Pi via the test points while doing this (rather than ramping up the voltage blindly). One of the nice things about the low cost of the Raspberry Pi is I feel a bit less worried about damaging it ;)

I had the 40m 24V PoE setup running indoors for a few weeks (filming mice invading the house), and noticed every so often the Pi would lock up. The webserver stopped responding, I couldn't SSH in. After rebooting I could see it had also stopped recording images. I didn't establish if this was an intermittent power issue, some other hardware issue (overheating in the closed case I was trying perhaps) or a software problem.

I'm intending to use the 40m 24V PoE setup in my garden this spring (for monitoring bird nesting boxes rather than telescope usage).

ant_thomas
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Re: A DIY PoE solution

Tue Jan 01, 2013 3:28 pm

I've made a homemade POE system for an RPi that lives outside.

It uses an old 24V (I think 550mA) power supply and both of the spare pairs. The ethernet cable is 50M CAT5E.

I had a spare 2 pair ethernet cable lying around so cut that in half and spliced it in to save me putting connectors on.

At the Pi end I've got a 5V UBEC to change the 24V down to 5V. In reality it's not 24V when it gets to the UBEC because of the loss down the 50M cable, especially under load. It didn't seem to work with a 12V supply, probably too much loss.

A small page with a short guide for my outside RPi webcam

coyotebush
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Re: A DIY PoE solution

Fri Mar 01, 2013 8:16 pm

Here is a $25 POE solution for the Raspberry PI. There may be cheaper solutions, but this one works “out of the box”.

1) Cisco POES5 5V power over Ethernet splitter
Available from Newegg for $22.

2) Cable adapter
USB 2.0 Female To DC 5.5x2.1mm Female Power Supply Extension Cable Adapter
Available on E-Bay for $2.84

plugwash
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Re: A DIY PoE solution

Fri Mar 01, 2013 11:40 pm

Yeah that seems like a reasonable deal if you want to go the "IEEE standard POE" route. Note that price is only for the extractor, you will also need either an injector or a switch with PoE.

HairyPaul
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Re: A DIY PoE solution

Thu Mar 07, 2013 8:54 pm

Anothe alternative for 802.3af powerin a RPi
http://www.cclonline.com/product/44601/ ... r/NET1473/

I havn't tried it yet, but looking to use it to power it for some Pi progects at work

Paul

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Cancelor
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Re: A DIY PoE solution

Tue Sep 03, 2013 2:52 pm

I know most of the above do not deliver the power into the Ethernet plug of the RPi but If pins 4 and 5 were joined to each other and pins 7 and 8 were joined to each other and lets say 24volts applied would this damage anything on the RPi? Are these unused pins connected to anything?

If the above on it's own is safe I'm then thinking ahead to something more dangerous, e.g. soldering to the RJ45 pins on the back of the RPi. ( I know, bye bye warranty!)
Can't find the thread you want? Try googling : YourSearchHere site:raspberrypi.org

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Burngate
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Re: A DIY PoE solution

Tue Sep 03, 2013 4:06 pm

From the schematic http://www.raspberrypi.org/wp-content/u ... .2_027.pdf
The ethernet socket is like this:
RJ45.png
RJ45.png (13.48 KiB) Viewed 66172 times
As you can see, the unused pairs don't appear on the back of the socket, so you won't be able to access them on the board.

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Cancelor
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Re: A DIY PoE solution

Tue Sep 03, 2013 9:04 pm

humph!

very good link though, thnx for that :)
Can't find the thread you want? Try googling : YourSearchHere site:raspberrypi.org

dpenezic
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Re: A DIY PoE solution

Sat Sep 28, 2013 9:27 pm

Hi all,

you may look on follow link for POE module :

http://www.ebay.com/itm/271281967791

Reagrds,
Dubravko Penezic

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