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TikYAN
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PoE Modes on CRS354-48P-4S+2Q+RM

Sat Aug 27, 2022 11:16 pm

Hi Mikrotik Community,

on a CRS354-48P-4S+2Q+RM (48 Port PoE Switch), two devices didn't get power from the switch. (no log entry or something else)
i replaced an Cisco Catalyst 3750 and there the devices are up. Double-checked everything, seems the Mikrotik Switch force to have PoE Mode-B on the Ports, but my Device is a PoE Mode-A (Doorbird, https://www.doorbird.com/poe )... the old Cisco power all devices up, no matter if Mode A or Mode B.

The Mikrotik Help https://help.mikrotik.com/docs/display/ ... utpolarity
however other vendors can use opposite or Mode A pinout on PD. Reverse polarity would require using a crossover cable but Mode A PD would require Mode B to Mode A converter.
Are the Cisco's and some other "cheaper" PoE Switch Manufacturer are here more "tolerant" to accept both Modes?
Do someone know a "converter" for Gigabit? I have some PoE Injectors here, but my heart is bleeding to use an PoE Injector behind a PoE Switch...

Best Regards,
YAN
 
TikYAN
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Re: PoE Modes on CRS354-48P-4S+2Q+RM

Tue Aug 30, 2022 10:04 am

The Doorbird Mode A Devices are only 100M, can i rewire or change Pins for this ports on the Patchpanel to "convert" Mode A from the PD to Mode B to the Switch?

my thoughts are to change following Pins on the Patchpanel

Mode B (PSE) Pin 4 to Pin 1 Mode A PD
Mode B (PSE) Pin 5 to Pin 2 Mode A PD
Mode B (PSE) Pin 7 to Pin 3 Mode A PD
Mode B (PSE) Pin 8 to Pin 6 Mode A PD

"but Mode A PD would require Mode B to Mode A converter" is against my repinning :shock:

i found an Digitus DN-95130, but this is nowhere available (looks like an end of life product)
 
sindy
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Re: PoE Modes on CRS354-48P-4S+2Q+RM  [SOLVED]

Tue Aug 30, 2022 11:28 am

If you swap the pairs the way above (4,5 <-> 1,2; 7,8<->3,6), the FastEthernet devices will get power but not the Ethernet connection; while GigabitEthernet supports any arrangement of pairs, FastEthernet can only use pairs 1,2 and 3,6 and only their direction can change (MDI/MDI-X).

The whole thing is that connecting power to the data pairs requires a more complicated circuitry than connecting it to the unused pairs. So if you cannot find an off-the-shelf Mode B to Mode A converter, you can take the FE passive PoE extractor to get the power from (4,5; 7,8) to a barrel connector, connect a GE passive PoE injector to it with swapped pairs as above, and swap pairs back at the output of the GE injector. This way, you won't need an external power source, so you'll be able to control the PoE on the switch and thus power-cycle the connected devices.
 
TikYAN
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Re: PoE Modes on CRS354-48P-4S+2Q+RM

Tue Sep 06, 2022 10:06 pm

Thank you sindy, i'll try that!

i contacted also the vendor doorbird, they say, there is no option for re-wire and they didn't know a converter. I should use the Power Supply or an dedicated injector...

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