hEX PoE + 48v = 802.3af/at only B ?

vovanfz · February 19, 2019, 7:50am

Good day!

I have a question. Can hEX PoE with 48V 1.46A 70W adapter power equipment with 802.3af/at A mode ( like UniFi AC LITE - 802.3af Alternative A (1, 2+; 3, 6 -)) ?

https://mikrotik.com/product/RB960PGS says “It can power at/af mode B (4,5+)(7, compatible devices, if 48-57 input voltage is used.”

I thought that 802.3af/at it is standart, but it has two mode unexpectedly (A and B).

Thank you.

marekm · February 19, 2019, 10:22am

The two modes A and B are not unexpected, they are fully specified in the 802.3af/at standards.
Mode A is over the 10100 data pairs (12/36) and mode B is over the spare pairs (45/78) which are data pairs in gigabit too.
Compliant PD (powered device) must accept power in any one of the two modes (in practice, two bridge rectifiers in front of the PoE controller and DC/DC converter).
Compliant PSE (power sourcing equipment) is free to choose any one of the two modes (not both at the same time).
Latest PoE standards (802.3bt and some earlier proprietary solutions) extend this to support use of all 4 pairs for even higher power, but few devices support that yet.
PoE standards also specify detection (does the connected device support PoE), classifications (how much power does it ask for), disconnect detection (remove power after device is unplugged) and overload/short-circuit protection, passive PoE lacks these features so you must be careful to not cause damage by connecting incompatible devices.

vovanfz · February 19, 2019, 2:55pm

The two modes A and B are not unexpected, they are fully specified in the 802.3af/at standards.
Mode A is over the 10100 data pairs (12/36) and mode B is over the spare pairs (45/78) which are data pairs in gigabit too.
Compliant PD (powered device) must accept power in any one of the two modes (in practice, two bridge rectifiers in front of the PoE controller and DC/DC converter).
Compliant PSE (power sourcing equipment) is free to choose any one of the two modes (not both at the same time).
Latest PoE standards (802.3bt and some earlier proprietary solutions) extend this to support use of all 4 pairs for even higher power, but few devices support that yet.
PoE standards also specify detection (does the connected device support PoE), classifications (how much power does it ask for), disconnect detection (remove power after device is unplugged) and overload/short-circuit protection, passive PoE lacks these features so you must be careful to not cause damage by connecting incompatible devices.

Do you mean that hEX PoE with 48V 1.46A 70W adapter power doesn’t power a UniFi AC LITE ?