MikroTik RB960PGS hEX PoE powering PoE devices: ensure you get a 48V power supply
Posted by jpluimers on 2021/08/24
By default, the [WayBack] MikroTik RB960PGS hEX PoE comes with a 24V power supply.
Most PoE capable devices cannot be powered by 24V but need 48V. I wrote about this before in the midst of the long post Linus Torvalds – Google+: Working gadgets: Ubiquiti UniFi collection (and a whole bunch of Unifi/Ubiquiti/Ubtn links)
- Mikrotik needs to make up their mind, as they ship a 24V power supply which cannot power any 802.3af/802.3at devices. The 48POW power supply enables 802.3af for the RB960PGS hEX PoE: [WayBack] hEX PoE (RB960PGS) – Need 48V Power Supply – MikroTik
So now I re-mention it in a much smaller post so it easier to find back, and a few links to Power over Ethernet – Wikipedia, where especially these bits are relevant:
- The PoE Standard implementation for 802.3af (802.3at Type 1) “PoE” requires DC 44.0–57.0 V.
- Of the PoE Non-standard_implementations, some common Passive specifications include:
- 24VDC 0.5A 100 Mbit/s or 1 Gbit/s
- 24VDC 1.0A 100 Mbit/s or 1 Gbit/s
- 48VDC 1.0A 100 Mbit/s or 1 Gbit/s
- 56VDC 1.0A and 2.0A 1 Gbit/s (used for 45W+ load point to point microwave and millimeter band radios
The 24V is what MikroTik sticks to with their default power supply.
48V enables real 802.3af (802.3at Type 1) PoE.
Realising this helped me to remote control the power to:
- a Ring Stick-Up Camera (2018 model)
- a Raspberry Pi from a RB960PGS hEX PoE device using a UCTRONICS Gigabit PoE Splitter for Raspberry Pi 3B+.
Likely, the same holds for similar splitters, so I included some links:
- [Archive.is] AmazonSmile: UCTRONICS PoE Splitter Gigabit 5V – Micro USB Power and Ethernet to Raspberry Pi 3B+, Work with Echo Dot, Most Micro USB Security Camera and Tablet – IEEE 802.3af Compliant: Computers & Accessories
1pcs 48V to 5V Active PoE Splitters Micro USB Power Plug
- [Archive.is] UCTRONICS Gigabit PoE Splitter für Raspberry Pi 3B+, kompatibel mit PoE HAT, IEEE 802.3af auf 5V Micro USB: AmazonSmile: Computer & Zubehör
Power over Ethernet 802.3af kompatibel, Gigabit-Ethernet-Port, 10/100/1000M, 44-56V DC-Eingangsspannung, 5V 2A DC-Ausgang, liefert bis zu 2,5 A
- [Archive.is] SODIAL POE Netzteilmodul Standard isoliert Splitter 48V: AmazonSmile: Elektronik
12 W Micro-USB Power over Ethernet PoE bis zu Remote 328 – 492 ft (100 – 150 m) ueber Ethernet-Kabel, 802.3af PoE-Switch oder 48 V-Injektor wird benoetigt
- [WayBack] UCTRONICS – Wholesale for Electronics, Arduino and Raspberry Pi Modules, Robot Parts and IoT – UCTRONICS PoE Splitter Gigabit 5V – Micro USB Power and Ethernet to Raspberry Pi 3B+, Work with Echo Dot, most Micro USB Security Cameras and Tablets – IEEE 802.3af Compliant
Specifications:
Compliant with IEEE 802.3af
Isolation: 2.5kV
Input: 802.3af 44-56V Mode A&B 300mA
Power Output: DC 5V/2A(up to 2.5A) 10W
Data Transfer rate: 10/100/1000 Mbps
Devices will be detected before poe input
Power Pin: support both 1/2(+/-),3/6(-/+) or 4/5(+),7/8(-)Package Including
1pcs 48V to 5V Active PoE Splitters Micro USB Power PlugThe gigabit version update of UCTRONICS U5159 PoE splitter(ASIN:B01MDLUSE7)
You can read more about PoE splitters for Pi on our blog: https://www.uctronics.com/index.php/blog/uctronics-poe-hat-splitter-raspberry-pi-4-blog/
- [Archive.is] AmazonSmile: UCTRONICS PoE Splitter Gigabit 5V – Micro USB Power and Ethernet to Raspberry Pi 3B+, Work with Echo Dot, Most Micro USB Security Camera and Tablet – IEEE 802.3af Compliant: Computers & Accessories
PoE distances
I had a hard time finding out maximum distances for PoE cable length, as the information is disparate.
From the links below, I think the conclusion is that the maximum PoE length (or reach) is not limited by PoE, but by the network standard.
This reach seems 100 meters or 328 feet for active PoE:
- Ethernet: Varieties – Wikipedia
- Ethernet physical layer: Physical layers – Wikipedia
- Category 5 cable: Comparison with later standards – Wikipedia
- Ethernet over twisted pair: Cabling – Wikipedia
- [WayBack] PoE Calculator – POE Texas: Calculate Your PoE Power Budget and Troubleshoot Your Installation Free
- [WayBack] PoE calculator for Power over Ethernet:
- PoE calculator for Power over Ethernet, calculates required and delivered power and voltage drop for voltages from 5 to 56 volts
- [WayBack] Poe max distance? – Networking – Linus Tech Tips
- Q: Short and sweet. If I run a Poe camera on a 300 foot long Ethernet run. Will it function?
- A: If all devices conform to the 802.3x standards involves, yes, 328 feet max.
- [WayBack] Is there a length limit to PoE cable runs? – Help Center | EnGenius
- [WayBack] Ring Stick Up Cam Wired (2018) review: Ring finally has an indoor security camera | TechHive
The PoE option will also require you to run ethernet cable (up to 330 feet or 100 meters) to the camera.
Note that passive PoE has much shorter distances: Power over Ethernet: Passive – Wikipedia mentions 15 feet (4.6 meters) 5V because of the voltage drop.
Furthermore, for long cables, prefer CAT 5/E over CAT 6/6A:
[WayBack] Unexpected PoE / Cable length limitations with UniFi Switch-16-150W & UniFi AC-LR Access Points | Ubiquiti Community
What you are likely seeing here is something that will become more of a problem down the road – CAT6/6A cables are being made with 26 gauge cable.
The biggest problem with 10Gb ethernet is crosstalk between the wires/pairs in the cable. THere’s just one way to lessen this – move the wires physically farther apart. One way the cable mfgrs have found to accomplish this while not making the cable too large – there is actually a spec for the maximum diameter of ethernet cable – is to make the copper wire itself smaller, so the insulation is thicker, so there’s more space between conductors. This actually works ( and they love it because there’s less copper which saves them money, but they can charge more for the cable because, well, it’s spec’d higher, right?) , but it causes the problem you are seeing – the smaller conductor has higher resistance and therefore more voltage drop than the standard cat5e 24 gauge wire. So with longer cat6 cables ther PoE limitation needs to be accounted for. This is why I never use Cat6/6A cables except for very specific things, and never ever for PoE.
Change out your cable to cat5e and the problems will go away. And at gigabit speeds it will work just fine up to 100 meters, even at 24V PoE.
Permanent “on”
You might think plugging in a 48V power supply is enough, but that might not cut it.
The autonegation of PoE does not always work, which in this case did not.
Setting the “PoE Out” option of a MikroTik network interface from the default “auto on” to “forced on” then gets going.
At start-up, in text mode, the RaspBerry Pi+ with an attached Chromecast first generation draws about 3.8 Watt:
With a full blown graphic UI at 1920×1200 with moving graphics in Firefox draws slightly more, somewhere between 5.2 and 5.9 Watt (usually closer to 5.2):
–jeroen
The Wiert Corner - irregular stream of stuff 
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