Author Topic: SBC66EC PoE compliance  (Read 3045 times)

MaurizioB

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SBC66EC PoE compliance
« on: November 04, 2011, 01:09:36 AM »

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Hello,
I've seen that the new SBC66EC board supports PoE. Looking at the schematic it's possible to see D6 and D7 that take power both from the ethernet spair cable (4+5 and 6+7 RJ45 PIN) and from the central point of the line trasformers.
Does it means that if I connect the board to a PoE PSE it will power up?
I know that 802.3af (the PoE standard) it's more complex but I wonder if the SBC66EC PoE implementation can work on PoE PSE thanks to some "recovery" specification in the standard.

best regards,
Maurizio bertero
« Last Edit: May 31, 2012, 05:30:36 PM by modtro2 »

modtro2

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Re: SBC66EC PoE compliance
« Reply #1 on: November 04, 2011, 12:11:18 PM »
Hi, the SBC66EC is not a 802.3af PoE device. It uses a very cheap method of PoE by supplying power over the spare Ethernet pairs. You can buy power injectors from many different sources that will put power on the spare Ethernet pairs. Just do a Google search for "passive poe injector". Seems like it is quite common calling the non 802.3.af compliant injectors "passive".

Ensure the injector supplies positive power to Ethernet pair 7 and 8, and ground to 4 and 5. If it has + and - the other way round (unfortunately most seem to), simply reverse the polarity of the DC power plug. The SBC66EC has a protection diode on the 7,8 pair, so will not get damaged if the PoE voltage polarity is reversed.

sbell

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Re: SBC66EC PoE compliance
« Reply #2 on: November 15, 2011, 06:02:13 AM »
I would just like to say that proper 802.3af compliance is very cheap and very easy... essentially you just have to add a LTC4257-1, a few resistors, and a diode bridge.  I for one would like to see the SBC line get proper PoE support -- right now we are intercepting the ethernet connection, adding the PoE support, and then feeding the ethernet signal back to the SBC ourselves.

modtro2

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Re: SBC66EC PoE compliance
« Reply #3 on: November 15, 2011, 09:20:22 PM »
Thanks for tip! Want to create a device with proper 802.3af in the future. It does however add a couple of $ to total cost, and current solution is very cheap and just as reliable (maybe even more = less components) as standard. It can not provide as much power, but for many applications this is not issue, and cost is more important.

PLEASE NOTE that currently PoE is disabled on all SBC66EC boards at delivery. Can be enabled by making solder jumpers S3 and S4 on bottom of board. Next revision of SBC66EC (early next year) will have the polarity of the PoE pins swapped to the standard used by nearly all "Passive PoE Injector" manufacturers. That is positive power to Ethernet pair 4 and 5, and ground to 7 and 8. For current revision 1 boards this is reversed, and can be seen as a hardware bug. For this reason PoE has been disabled by default on all SBC66EC boards.
« Last Edit: November 15, 2011, 09:22:15 PM by modtro2 »