Hi guys, i noticed two rectifier bridges in the input side of the psu circuit of that board, and i wonder if it is possible that i feed 24v trough POE and the original 12v from the built in AC adapter at the same time, and since they will be isolated by the bridges, the 12v psu will take over in case of failure of the 24v supply?
(I assume that each power input enters one of the bridges, and they are muxed at the inductor );
is this setup possible, or i misinterpreted the implementation of those rectifier bridges?
I know on earlier versions of the RouterBoards it was not possible, however, I would like to know the answer to that as well. How about we test it with yours first
Somewhere on the forum, Normis posted that at least one model device was able to use two power supplies for the purpose of failover so long as the difference in voltage between the two power supplies was greater than 2v DC. It would run on the higher voltage and use the lower voltage supply if the higher voltage supply went away.
I do not remember if his comment included the RB1100AHx2 or not. It should be possible to find the post in the forum search.
We are using this productively on a number of 1100Hx2 and 1100AHx2 and had no problems so far.
24V power is fed through PoE, and 12V through the internal AC adapter - you can happily plug each one out or in without any service disruption
@guipoletto, thank you for starting this thread. I actually read about this new feature as it wasn’t available in their previous versions and was a bit confused. I wasn’t actually in a mood to experiment because it’s not easy for me to get a delivery here. Thank you guys again guys for trying it out first and giving confidence to guys like me who can’t really afford burn outs.
We had a problem with this a year ago, but I believe it was due to a faulty PoE (Ubnt).
The unit powered normally VIA PoE, and when we attempted to do a test failover, the capacitors on the board exploded. (Violently lol!)
We noticed however, after testing the same PoE, it would not power anything. All we had done was disconnect it from the RB. So it probably was broken before and we didn’t know it. First and last time we saw this happen. No other problems since, but it was a surprising (And smokey) experience lol.
Here’s something odd I’ve found with using Ubiquiti passive PoE injectors to power RB1100AHx2: with a newer-style injector [with the white LED] you can power up the unit and run it fine. You can move to internal PSU fine [ie, apply power to internal PSU, remove power from injector/port 13]. However, when you try to move back to the PoE after running on internal PSU, the unit reboots! One way you can tell it’s not going to work when you reconnect the injector, the LED on the injector pulses about once a second, and the fans don’t speed up [I assume fan speed is linked to voltage - injector voltage is 22.9v, internal PSU is 12.2v].
The older models of Ubiquiti injector [with the green LED, and no reset pinhole on the back] work fine. Fail back and forth 20 times with no issue. Input voltage shows as 22.4v.
So I guess someone’s going to tell me, the moral of the story is don’t use use Ubiquiti PoE injectors
What is the amp rating of the new UBNT PoE units? What is the amp rating of the old PoE units?
I really expect the amp rating to make more difference than half a volt between 22 and 23 VDC.
Unfortunately, I do not see power requirements for the RB1100AHx2 on routerboard.com.
My RB1100AHx2 running 5.26 doesn’t show current draw in /system health output. I do see other posts with RB1100AHx2s where they seem to draw around 1 amp at 12vdc for 11 to 12 watts power consumption. Your PoE injector would need to be at least 0.5 amps at 24vdc. I would want to have at least another 0.1 amp to allow for in-rush current. UBNT uses 0.5 amp at 24vdc injectors for their 6 - 8 watt devices.
I have an 1100AH and do exactly the same.
I also do the same thing on rb750UP
Indeed as someone else stated, normis told me once that ALL boards that can have both power supplies do work with both. Off course the voltages have to be within the limit of specs…
Confirming here another AHx2 user - I plug the PoE injector on the front and have normal power in the back, can unplug either of them without disruption, use it quite a bit for re-organising rack cables.
The old and new ubnt injectors will redundantly power a CRS125-24G-1S-RM back and forth no problem. So I guess it a current draw problem with the new-style injectors as the CRS125-24G-1S-RM presumably draws much less than the RB1100AHx2.
