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Power from ethernet? — Parallax Forums

Power from ethernet?

Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
edited 2011-02-23 19:21 in Accessories
I suspect I already know the answer, but any chance we can grab enough power from the Ethernet connection to power this thing? It' would be a hack for sure, but would be interesting to just drop it next to my router on a short piece of CAT5 and see it simply take off.

OBC

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-11-10 22:08
    OBC,
    Do a little research first ... hmmm ... all it takes is a web search.

    You'll need a switching regulator with a high enough voltage rating, but it's certainly doable.

    See here
  • W9GFOW9GFO Posts: 4,010
    edited 2010-11-10 22:15
    Just skimming the documents but it seems like PoE requires injecting power into the line whereas I think OBC was talking about harvesting the power that is already there in the data signals.

    Rich H
  • Mike GreenMike Green Posts: 23,101
    edited 2010-11-10 22:30
    Ethernet doesn't normally provide power. The data signals don't provide any significant amount of power. You have to deliberately provide it and this is called PoE (Power over Ethernet). There are routers that provide this and you can buy adapters that "inject" power upstream. This is often used for wireless Ethernet links that get mounted outside or inside in remote places in a building without power close at hand.
  • schillschill Posts: 741
    edited 2010-11-11 05:09
    You can always add fake POE over the unused lines of an cat 5/6 cable. Typically 4 of them are not used for data. There are some injectors you can buy that do this but you can also do it yourself. Doing POE based on the real standard is usually quite a bit more expensive. Also, the POE standard uses 48 VDC which requires fancier hardware at the receiving end than a simple voltage regulator. I assume the 48 V is to allow for voltage drops over long runs but I haven't looked into it.

    If you fake it and inject whatever you want you can work with lower voltage levels. Just build a cable adapter at one end that allows you to pass through the 4 data lines and input your power to the other 4 lines. At the receiving end, you build an adapter that does the opposite. I have run 9 volts over several hundred feet of cat5 and still had enough headroom at the far end to feed a 5V regulator. I tested with 1000 feet but I forget what the results were.

    I don't think it will be easy to build this directly into the Spinneret board, however. You would need a simple adapter (this can really just be a modified cable) at the Spinneret end to break out the power instead. Looking at the schematic for the RJ45 magjack, it doesn't look like it's easy to connect to the 4 unused pins to pull the power out directly from there. You'd have to do it slightly upstream.

    This is one of the first things I looked at when the Spinneret was officially released (right after I ordered mine (which arrived yesterday :) )).
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2010-11-11 05:33
    It's been a while since I did any interesting networking...

    Yes, I was referring to grabbing some of the power that is there.
    I've noticed that there is generally enough power to light a couple LEDs on the jack on a NIC without having power applied to a PC. From your answers, it looks like this isn't enough juice to make things interesting.

    Thanks
    OBC
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2010-11-11 08:23
    So I guess you weren't the one that picked up the PoE power supply/injector that I had sitting on the freebie table at the last UPENE show? That was one of the many treasures I donated to the freebie table.....

    Robert
  • BradCBradC Posts: 2,601
    edited 2010-11-12 04:50
    Oldbitcollector wrote: »
    Yes, I was referring to grabbing some of the power that is there.
    I've noticed that there is generally enough power to light a couple LEDs on the jack on a NIC without having power applied to a PC. From your answers, it looks like this isn't enough juice to make things interesting.

    No _way_. Ethernet is transformer isolated. I'll lay a carton of beer and 2 bottles of scotch that you can't get the lights on a NIC to light up with only an ethernet cable attached. In fact, I'll wager another bottle of scotch on the ethernet card being powered from the +5V stby line on the PSU (5 volts, on all the time the PC has a plug in the back of it) to allow the NIC to detect a WOL packet and wake the PC up.
  • Beau SchwabeBeau Schwabe Posts: 6,559
    edited 2010-11-14 00:17
    BradC is correct...

    There are 4 differential pairs of wire on Ethernet that are isolated with a transformer that form the total of 8 wires that you see. In order to get POE you need to break that code and have at least two devices ... one designed to send power while the other is designed to receive power. ... in most cases other devices on the Ethernet line that are not POE capable will not be affected if there is power present or not.
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2010-11-14 10:52
    BradC wrote: »
    No _way_. Ethernet is transformer isolated. I'll lay a carton of beer and 2 bottles of scotch that you can't get the lights on a NIC to light up with only an ethernet cable attached. In fact, I'll wager another bottle of scotch on the ethernet card being powered from the +5V stby line on the PSU (5 volts, on all the time the PC has a plug in the back of it) to allow the NIC to detect a WOL packet and wake the PC up.

    I don't drink beer or scotch, but I know that I have witnessed this on more than one occasion. It actually caught my eye because it was so strange. Being in the PC repair business I get all sorts of different PC configurations pushed across my desk for repair. Next time I get one that does this I'll grab my video camera and lay proof that I've seen it. :)

    OBC
  • FranklinFranklin Posts: 4,747
    edited 2010-11-14 13:16
    Next time I get one that does this I'll grab my video camera and lay proof that I've seen it. :)
    Just make sure the computer isn't plugged in when you test this.
  • Beau SchwabeBeau Schwabe Posts: 6,559
    edited 2010-11-14 14:40
    This is a standard POE connection ...

    supply_diagram.png

    Here is a link showing the above configuration and other possibilities.

    http://hw-server.com/docs/power_over_ethernet-PoE.html

    The maximum allowable amount of power that you can transfer is about 31 Watts (62 Watts if you double up and use the spare pair), but in order to transfer any power at manageable DC voltages, you must use DC-DC converters.

    The maximum voltage allowed is about 57V
    The maximum current allowed is about 550 mA

    57V X 550mA = 31.35 Watts <-- however, read the conclusion at the bottom of the link I posted, about
    the amount of true available power due to I/R drop
  • EricxEricx Posts: 2
    edited 2011-02-19 04:55
    Most corporate IP phones are POE, they usually have an embeded browser as well.
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2011-02-19 22:35
    PoE and the Spinneret is an excellent match up. The problem is cost of injectors/power modules. You can fudge PoE quite a bit for your needs even if it to put the Spinneret in a location that you only want to run Cat5. I have a few PoE power modules that output 12v and 5v, but haven't played with them yet. My plan for LED Christmas lights is to run Cat5 to breakout boxes using a PoE style setup to a light controller.
  • Ding-BattyDing-Batty Posts: 301
    edited 2011-02-20 08:23
    Very interesting.. I just searched for PoE devices, and found the Cisco POES5, which provides 5V to the attached device (like the Spinnernet). This is available several places for about US$20 to $25. All you'd need in addition is another device to inject the 36V to 57V (48V nominal) onto the Cat5 cable, and Spinnernet could be operated over a single wire -- convenient.

    I'm sure there are cheaper ways to get the Spinnernet power from Cat5, but this is much easier in small quantities.
  • pthartmannpthartmann Posts: 27
    edited 2011-02-22 19:18
    This looks like an affordable option: LINK $34.99

    Newegg.com, Walmart.com, and Amazon.com carry the D-Link, but Amazon has free shipping and no tax.
    Product Features

    • Transmit power and data over 1 cable up to 328 feet (100 meters)
    • Eliminates the need to place an Ethernet-enabled device near a power outlet, giving you more freedom in placement
    • Easy plug-and-play installation requiring no tools and no software
    • Gives you greater flexibility in your Ethernet-enabled device installation
    • Adjustable 5V or 12V power output

    Technical Details

    • Brand Name: D-Link
    • Model: DWL-P200
    • Width: 8.19 inches
    • Height: 2.59 inches
    • Weight: 1.26 pounds
  • kuismakuisma Posts: 134
    edited 2011-02-22 22:25
    pthartmann wrote: »
    • Brand Name: D-Link
    • Model: DWL-P200
    • Width: 8.19 inches
    • Height: 2.59 inches
    • Weight: 1.26 pounds

    Please note that many cheep "Power over Ethernet" are not Power over Ethernet (802.3af) compliant, but only acts as a connector transmitting power over spare pairs in the tp cable. Those units will not work with other PoE equipments, e.g. switches etc. This D-link is such an example of a non standard unit.

    http://en.wikipedia.org/wiki/Power_over_Ethernet
  • pthartmannpthartmann Posts: 27
    edited 2011-02-23 18:34
    That's a good observation.

    If one is trying to power more Spinnerets or Network equipment, I suppose they would have more money for a compliant unit.

    In the meantime, for those who simply want to power up their Spinneret, it might be hard to find a cheaper commercial alternative.

    I also noticed that Amazon is probably providing "shipping specifications" or else, this unit may be pretty heavy.
  • schillschill Posts: 741
    edited 2011-02-23 19:21
    Switches which output POE power are quite a bit more expensive than those that don't. The cheapest I see at www.newegg.com is $64 - an 8 port switch with 4 ports supporting POE.

    You would still need something at the other end to extract the power.

    The D-Link "fake POE" is useful if you only have one device you need to connect.
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