varying PoE mA/W output

Hardware MikroTik hardware general
1

Hello,

I have my first routerboard product, an RB750UP. I’m not doing anything terribly complicated, it’s basically acting as an ethernet/PoE repeater on a long run. We have about 200 feet of cable from the PoE injector to the RB (port 1), and then another 250 to a Ubiquiti Rocket M5 (off of port 2). There was no problem getting power that far without the RB, but at that distance we couldn’t get more than 10Mb/s on the ethernet.

The RB750 was installed today and it seems to be working, but with a few caveats that I wanted to check on:

-With PoE set to “auto” this wasn’t working. The RB had no issues powering itself, but the Ubiquiti on port 2 was going up and down every minute or so. When I got into the RB remotely I saw PoE and the link to the Ubiquiti were in fact dropping. I set PoE to “forced on” and so far there have been no further issues. Is it supposed to be necessary to have “forced on” set? Any issues with leaving it like that?

-When monitoring port 2 from the web UI or the cli, I see the power output, both mA and watts varies wildly. Is this normal behavior? The Ubiquiti seems to be not having any issues, so I’m assuming it’s some odd measurement glitch. Is this indicating any sort of problem?

Here’s some info…

A sample of the power output:

[admin@568-roof-switch] > interface ethernet poe monitor 0 without-paging
             name: ether2-master-local
  poe-out-voltage: 21.2V
  poe-out-current: 816mA
    poe-out-power: 17.2W

             name: ether2-master-local
  poe-out-voltage: 21.2V
  poe-out-current: 0mA
    poe-out-power: 0W

             name: ether2-master-local
  poe-out-voltage: 21.2V
  poe-out-current: 856mA
    poe-out-power: 18.1W

             name: ether2-master-local
  poe-out-voltage: 21.2V
  poe-out-current: 732mA
    poe-out-power: 15.5W

             name: ether2-master-local
  poe-out-voltage: 21.2V
  poe-out-current: 0mA
    poe-out-power: 0W

             name: ether2-master-local
  poe-out-voltage: 21.2V
  poe-out-current: 96mA
    poe-out-power: 2W

             name: ether2-master-local
  poe-out-voltage: 21.3V
  poe-out-current: 48mA
    poe-out-power: 1W

             name: ether2-master-local
  poe-out-voltage: 21.3V
  poe-out-current: 776mA
    poe-out-power: 16.5W

And info about what I’m running:

[admin@568-roof-switch] > system resource print
                   uptime: 5h31m29s
                  version: 5.24
              free-memory: 19228KiB
             total-memory: 29696KiB
                      cpu: MIPS 24Kc V7.4
                cpu-count: 1
            cpu-frequency: 400MHz
                 cpu-load: 1%
           free-hdd-space: 89580KiB
          total-hdd-space: 126976KiB
  write-sect-since-reboot: 873
         write-sect-total: 34159
               bad-blocks: 0%
        architecture-name: mipsbe
               board-name: RB750UP
                 platform: MikroTik
2

please note that this is not a measuring device and voltage reading may flow a bit. However precision is decent enough to see if there are some PSU issues coming or similar.

3

Is there a way to calculate a rough average? I mean, it’s swinging from almost a full amp, which seems a bit crazy, all the way back to 0…

4

Yes that’s the way PoE works.
Radios are NOT transmiting a “flat line RF power”
They transmit in digital form with a LOT of ups and downs so their current that they are drawing, will be shown in the monitor with ups and downs - don’t worry, this is normal.

“Forced On” instead of “Auto” >
In “Auto” mode when RB750UP shuts down or restarts, it will give you output voltage to Ethernet ports and STAYS there.
In “Forced On” mode when RB750UP shuts down or restarts, it will give you output voltage to Ethernet ports BUT it gives it ONCE, then it CUTS it down and then it gives it AGAIN - This way when the other divices gets this voltage, they will start booting BUT they will stop booting after 1sec and then they will boot again.

5

I should probably point out the radio has no subs on it yet, it’s idle.

I also really don’t follow the “force on” vs. “auto” - in my case “force on” is the only thing that works. “auto” seems to just randomly cut power to the radio…

6

Yes in your case, leave it to “Forced On”.