For a very long time, Ubiquiti has been using 24v passive PoE in a lot of its devices, apart from the original NanoStation2 which used 12v passive PoE. The IEEE standard for active PoE has been around since 2003, which pre-dates Ubiquiti as a company - so why did they use any form of passive PoE?

Why passive PoE?

It might not be that obvious anymore to a lot of people, but Ubiquiti got its start in the WISP and wireless industry with the original NanoStation2 being its most notable. A device launched in the first few years of the company. This device was later replaced by the NanoStation M2 and other 'M' series devices starting in 2010. The NanoStation2 used 12v passive PoE and could handle a maximum throughput of 25mbps over 15km, or more using an external RP-SMA antenna.

At the time the active PoE standards were still finding their feet and it must be said that at the same time, the entire WISP industry was using passive PoE with the likes of Cambium (née Motorola) and Mikrotik. Ubiquiti wasn't the huge and notable company it is today so adopting the most common standard at the time was in its best interest, so customers would be interested and it would work with existing PoE setups.

The other argument for passive PoE vs active PoE in WISP environments is the communication that happens between devices. WISP towers are often in remote locations, in extreme temperatures and operators need to be 100% sure that power to uplink and downlink devices is going to remain on. Not that active PoE is unreliable, but the last thing operators want is devices to go offline.

Lastly is solar, which uses 12v batteries and are typically doubled up to produce 24v power for devices such as the NanoStation AC for providing network connectivity and cameras for various applications such as wildlife watching and traffic cameras.

Which Ubiquiti devices use passive PoE today?

Ubiquiti has a fair few amount of devices available which use 24v passive PoE today, apart from one device the entire UISP device lineup, including airMAX, UISP Routing & Switching, EdgeMAX and LTU use 24v passive PoE. The only device emitted from this list is the NanoStation 5AC which is somewhat of a unicorn as it can be powered by both 24v passive PoE as well as 802.3af active PoE.

The UISP Routing & Switching devices use 27v passive PoE, but retains full compatibility with 24v passive PoE devices. The extra few volts is there to help cope with extreme temperates, voltage drop over long cable runs and generally help keep devices more stably powered.

In the UniFi side of Ubiquiti, the company stopped adding in 24v passive PoE into its current line of switches and APs a while back, in around 2016. The AC-Lite and AC-LR were first sold as 24v only devices but a new refreshed model was later added which supported both 24v passive and 802.3af. Elsewhere in the UniFi lineup is the UAP-AC-Mesh which also supports both 24v and 802.3af.

Conclusion

Generally speaking, the enterprise world of PoE devices has pretty much moved away from passive PoE and into using active PoE. This means devices talk to each other and negotiate how much power they need and the device providing the power will supply it. As for passive PoE in the WISP world, it is pretty much here to stay it seems. There is a legacy world of 24v passive PoE devices out there and as mentioned, it has better support and efficency when it comes to solar applications.

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