Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 9 of 9

Thread: [4.1] Power-over-Ethernet solution?

  1. #1
    Senior Member
    Join Date
    Jul 2020
    Posts
    174

    [4.1] Power-over-Ethernet solution?

    I'm assuming that the Ethernet solution sold in the PJRC store doesn't handle PoE. Can anyone recommend an alternate solution that will connect to the Teensy 4.1 in the same way as that, but also provide power?

    This one feature would make deploying multiple Teensies far easier. All you'd need is a PoE switch, and you could forget about buying/wiring multiple power supplies. Power and data over one cable!

  2. #2
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    12,398
    That seems a valid assumption.

    It would take a capable magjack and appropriate additions to the PCB to get usable power out and also getting the same six pins ready to attach to the T_4.1 - not seen that done yet.

  3. #3
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    I assume it would be the same six-wire cable, plus another two for GND/VCC.

    I saw some cheap-ish passthrough solutions on Amazon, but they're too large to comfortably use in a small enclosure.

  4. #4
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    12,398
    Quote Originally Posted by Pilot View Post
    I assume it would be the same six-wire cable, plus another two for GND/VCC.

    I saw some cheap-ish passthrough solutions on Amazon, but they're too large to comfortably use in a small enclosure.
    Actually searched and read this : planetechusa.com/what-is-gigabit-ethernet/

    Seems that 60Hz power can go over two unused pairs as it was first done with 100 Mbit - but that link says it also works with 1 Gbit and the power can be placed on all four pairs and still deliver 1 Gbit. So it takes a paired setup for how the power is injected at the source - then the end magjack that pulls power off the the right powered pairs.

    The power and signal on POE is AC AFAIK and that is why the magjacks have transformers in them to get the signal off - then it takes alternate means to bleed off the power inserted - then the voltage needs to be made DC and stepped down for use.

  5. #5
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    Looks like this would do the trick: https://www.mouser.com/Search/Refine?Keyword=MAX5995B

  6. #6
    Junior Member
    Join Date
    Jul 2020
    Posts
    6
    There are two versions of the module for the Teensy 4.1 Ethernet, and I am not sure if either one is valid. For POE both will not work. The PHY is DP83825 by TI for the Teensy 4.1. This PHY has a few recommendations in the datasheet under application information. Page 93 for Magnetics information. There is also a evaluation board made by TI for this part. TI discloses its schematic which makes recommendations for certain things.

    I would recommend NCP109x series for basic POE this will work for the first revision only which means up to 12.95 watts at the device side. You will need a high voltage switch mode regulator. (Modules are available for around 20 dollars which do this for you at around 85 percent efficiency.) There is a evaluation board for either the NCP1090 or NCP1094, with full schematic.

    POE changes the wire side termination and uses the center taps for power extraction. Most of the work is on the wire side of the magnetics. You can buy magnetics which include most of the recommended logic but it is time consuming and much more expensive.

    I am not sure the center taps on the device side should be wired together. I have not found any documentation for this configuration, but my search is limited. I do not know if the wire length is an issue for the PHY or not connecting to the module. However reworking to fix this and add POE should be straightforward.

  7. #7
    Junior Member
    Join Date
    Jul 2020
    Posts
    6
    Quote Originally Posted by Pilot View Post
    I assume it would be the same six-wire cable, plus another two for GND/VCC.

    I saw some cheap-ish passthrough solutions on Amazon, but they're too large to comfortably use in a small enclosure.
    This will work for retrofitting POE into the existing device. However it is not IEEE POE. Many times this is done to cut cost. High voltage switch regulators are a little more pricy and can have efficiency issues depending on the target voltage. The reason for high voltage is to avoid wire loses and/or damage. If you need small amount of power this may work. Note this will only work on 10/100 since those only use 2 of the 4 ethernet pairs. (This PHY is 10/100.) Passive adapters put power on the unused pairs. (One pair for positive and one pair for negative.)

    You will lose voltage with wire length. High current will heat up the wire. So use cation when doing this. 12 or 24 volts is pretty common, which will likely still mean switch mode regulator.

    I do not recall if IEEE POE uses active signaling or not on the lower version of the protocol. However support of IEEE POE injectors is not likely and they will send power over 58 to 35 volts DC depending on revision. Also Ethernet cabling category matters somewhat. Point being it will technically be power over ethernet but it will not be proper power over ethernet.

  8. #8
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    I would want to use the highest power delivery possible, which I think is 90 watts at the source and ~70 watts guaranteed at the powered equipment. Some of the newer source equipment will sense how much power is needed, and send only that much, so you are not wasting too much energy.

    If 70 watts seems like a lot, just consider driving some combination of LEDs and servos/steppers, or a touch-screen. Or all three of those things.

    I am not too worried about the wire. They are using high voltage so they can stay away from high amperage.

  9. #9
    Junior Member
    Join Date
    Jul 2020
    Posts
    6
    Quote Originally Posted by Pilot View Post
    I would want to use the highest power delivery possible, which I think is 90 watts at the source and ~70 watts guaranteed at the powered equipment. Some of the newer source equipment will sense how much power is needed, and send only that much, so you are not wasting too much energy.

    If 70 watts seems like a lot, just consider driving some combination of LEDs and servos/steppers, or a touch-screen. Or all three of those things.

    I am not too worried about the wire. They are using high voltage so they can stay away from high amperage.
    This is probably worth a glance:
    https://en.wikipedia.org/wiki/Power_...implementation

    You can buy prebuilt modules which extract the power from the wire. They are PD controller evaluation boards and some are a little pricy, but it would work. These may not have the switch mode regulator. You can find switch mode regulators as module, some of which are intended for use with POE. Many are available on digikey/mouser/etc. Networking vendors may also make ready to use models.

    A while back there was proprietary POE extensions before the latest POE standards were released. Both cap at ~70 watts. Some switch mode regulators did not like going for 56 to 3.3 volts. They took to going to 12 volts better. It depends.

    As for the power, there are many usages for POE. Especially under IoT/automation. However for LEDs there are lots of games you play to get the power down.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •