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TomjNorthIdaho
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48-Volt POE-Out switches

Thu Dec 31, 2020 11:38 pm

48-Volt POE-Out switches

I'm looking for some 48-Volt 24-port-Ethernet POE-Out switches that also have one-to-four SFP+ ports.

At most of my towers I already have the 48-Volt telco-grade power-supplies. I am trying to figure out what Mikrotik products can run on 48-Volts and have 12 or 24 or 48 Ethernet POE-Out ports and also has some SFP+ ports.

Does the Mikrotik PW48V-12V85W for ±48 V power supply work in any POE-Out switches ?
Does the Mikrotik PW48V-12V150W for -48V power supply work in any POE-Out switches ?
 
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Re: 48-Volt POE-Out switches

Fri Jan 01, 2021 12:45 am

The only Mikrotik switch with 24 PoE out ports and SFP cages is CRS328-24P-4S+. However it comes with built-in power adapter. Which means you'd have to replace it with ... hmm ... DC-DC bridge. The problem is that Telco-grade DC power is -48V, but Mikrotik takes +48V. If you directly applied Telco power, you'd likely experience some shortcuts because Telco gear uses chasis as positive pole while Mikrotik uses chasis as negative pole.
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Re: 48-Volt POE-Out switches

Fri Jan 01, 2021 1:42 am

 
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Re: 48-Volt POE-Out switches

Fri Jan 01, 2021 3:52 am

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Re: 48-Volt POE-Out switches

Fri Jan 01, 2021 12:59 pm

Which means you'd have to replace it with ... hmm ... DC-DC bridge. The problem is that Telco-grade DC power is -48V, but Mikrotik takes +48V. If you directly applied Telco power, you'd likely experience some shortcuts because Telco gear uses chasis as positive pole while Mikrotik uses chasis as negative pole.
In situations like this, you should always use an isolated power supply, just like you would when powering from the mains.
So a switchmode supply that takes 48V, converts it to 25kHz (or so) AC, transforms it about 1:1, then rectifies the output to make 48V DC again to power the equipment.
 
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Re: 48-Volt POE-Out switches

Mon Jan 04, 2021 10:48 pm

In looking through my inventory , I found a Mikrotik netPower 16P
It appears to be just what I was looking for :)
- two SFP+ ports
- 16 Gig POE Ethernet ports
- 48 Volt DC input and also a 24 Volt DC input.

So , by tomorrow , I will have this:
SFP+ #1 1-Gig fiber
SFP+ #2 10-Gig fiber
16 POE ethernets to run my APs.
24-Volts DC from an AC wall transformer power supply
48-Volts DC from my commercial grade 48-Volt DC system.
I will then use SNMP to alert me when the AC utility power goes out because the 24-Volts will drop , and the system will still continue running on the 48-Volts battery system.
I already pre-tested it on my desk to verify it will do what I want/needed.

Note - the Mikrotik netPower 16P only draws 24 & 48 power - it is NOT a battery charger also. However the POE ethernet ports will still supply POE over ethernet.

North Idaho Tom Jones
 
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Re: 48-Volt POE-Out switches

Tue Jan 05, 2021 3:07 am

Well - maybe the Mikrotik netPower 16P might not be what I want.

The netPower 16P has two DC connectors.
- A 24-Volt DC connector
- A 48-Volt DC connector

From what I am discovering:
- If you want to run 24-Volt POE devices , then you need the 24-Volt DC powered up using an external 24-Volt DC system.
- If you want to run 48-Volt POE devices , then you need the 48-Volt DC powered up using an external 48-Volt DC system.
- If you want to run both 24-Volt POE devices and also 48-Volt devices , then you need both the 24-Volt and 48-Volt DC connectors both powered up at the same time.
*** It appears that there is no built-in 48-Volt to 24-Volt voltage regulator inside the netPower-16. Thus If you have a an external 48-Volt DC system , then you are limited to only powering 48-Volt POE devices.

Another much more potential serious issue is the following:
- When powering the netPower-16P from my -48 telco-grade DC system, I measure 48 Volts between my rack-mount chassis ( my equipment shelter ground ) and anything metal on the Mikrotik netPower-16P. This includes the ground screw on the Mikrotik netPower-16P !!!
Thus , I suspect if I connect a ground wire from the Mikrotik netPower-16P to my NOC equipment ground or chassis ground , the results will be smoke and fuses will blow !!!
Also , I assume that if I connect any data cables which have a grounded-shield , that smoke and fuses will blow !!!

Soooo, in summary , the netPower-16P can never be connected to normal standard -48 telco power ( or you risk smoke and blowing fuses ). Note, normal telco 48-Volt systems are positive ground. The Mikrotik netPower-16+ is negative ground.
What in the heck were the Mikrotik hardware designers thinking when they designed the power input electronics on the netPower-16P ???

So, IMO, the Mikrotik netPower-16P is almost a useless devices because of the following:
A) - The netPower-16P should be DC power input leads isolated from ground/chassis-ground.
With isolated DC inputs, the user can then use the netPower-16P on standard-telco neg 48 DC power systems ( positive ground ).
With isolated DC inputs, the user can then use the netPower-16P on +48 volt DC power systems ( negative ground )
With isolated DC inputs, the user can elect to use no ground and just power with 48 Volts , and optionally ground the chassis.

B), The netPower-16P should be able to be powered using a single 24 or a 48 volt DC power system - NOT BOTH AT THE SAME TIME.

C), IMO - the Mikrotik netPower-16P should never be used with any normal standard telco neg-48-volt devices ( neg-48 volt routers or switches ) , because there is a serious potential to smoke and blow fuses if you connect any cables with a shield or ground between the two devices.

Will somebody please confirm my findings or correct me if I am wrong.

North Idaho Tom Jones
 
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Re: 48-Volt POE-Out switches

Wed Jan 06, 2021 12:38 am

The fact that MT devices don't have voltage regulators for PoE-out is well known.
The fact that MT devices taking 48V are not suitable for telco -48V is mentioned in my post #2 above.
The fact is that any shielded cables should have shield connected single-sided ... not only due to systematic voltage differences (such as +48 VS -48V devices) but due to usual stray currents (which can "only" disturb data transfers or cause excessive corrosion) as well.

MT devices with dual power input can be connected to different voltages at the same time. Usual devices (with only passive PoE-out or none PoE-out) will run off the power source with higher voltage (simple diodes used on power inputs). Devices with selectable PoE-out voltages need both voltages connected and PoE-out is then selected between two sources. Device itself still falls-back to the available power source in case one fails, PoE-out can not however.
Last edited by mkx on Wed Jan 06, 2021 12:47 am, edited 1 time in total.
BR,
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Re: 48-Volt POE-Out switches

Wed Jan 06, 2021 12:45 am

The fact that MT devices don't have voltage regulators for PoE-out is well known.
The fact that MT devices taking 48V are not suitable for telco -48V is mentioned in my post #2 above.
As much as I like the thousands of Mikrotiks I have in my WISP/ISP, I can't help but feel guilty that I'm going to have to purchase a dozen switches from somebody else. It would be nice if Mikrotik has a product similar to this: https://netonix.com/wisp-switch/ws-26-400-idc.html
 
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Re: 48-Volt POE-Out switches

Wed Jan 06, 2021 12:49 am

The device you linked is a highly-specialized device with apropriate price tag. Not every vendor has similar device in their offering, neither has Mikrotik. But yes, I can feel your pain, brother.
BR,
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Re: 48-Volt POE-Out switches

Wed Jan 06, 2021 12:55 am

mkx ... Hey if everything was easy and everything was available , there would be no need for Network Engineers ... so ... in that sense ... I guess I am pretty lucky

I will give it to Mikrotik, most of their products are pretty awesome to the to the experienced admins who need to build advanced ( wireless ) networks.

North Idaho Tom Jones
 
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Re: 48-Volt POE-Out switches

Wed Jan 06, 2021 1:11 am

You could use a Meanwell DC-DC converter like - https://www.meanwell-web.com/en-gb/dcdc ... sd-200c-48 for the 48VDC and a similar one for the 24VDC with the netPower 16P. Note this particular DC-DC is only 200W and the netPower 16P can require more if fully loaded.
 
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Re: 48-Volt POE-Out switches

Thu Jan 28, 2021 12:28 am

Best bet is to power netpower 16P with 48v and injecting Poe for 24v and isolating the switch from other DC racks by using fiber to connect between rack mounted equipment and netpower 16P.

Good luck
 
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Re: 48-Volt POE-Out switches

Thu Jan 28, 2021 3:17 am

Best bet is to power netpower 16P with 48v and injecting Poe for 24v and isolating the switch from other DC racks by using fiber to connect between rack mounted equipment and netpower 16P.

Good luck
re: isolating the switch

IMO , all DC power inputs ( both positive and negative ) should not be bonded to ground. ( aka internal DC isolated power supply ). Only the physical chassis should be bonded to ground - and all grounds should be bonded together as a common earth ground.
With isolated DC power supply and isolated devices using internal isolated power supply , there is no ground-loop problems.

however ....
When you have a telco neg 48 DC ( -48 ) with a positive ground connected to a 48-volt device that has a negative ground , then you have one potential serious hell of a ground-loop problem - as sparks will fly and smoke spewing out of something and fuses popping and things quickly turning black and brown.
 
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Re: 48-Volt POE-Out switches

Thu Jan 28, 2021 3:24 am

Ground loops can be a problem . I came across this many years ago with telex printers at a limestone quarry where the local ground potential was about 1000v different from the local telephone exchange. tread carefully
 
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Re: 48-Volt POE-Out switches

Thu Jan 28, 2021 3:37 am

Ground loops can be a problem . I came across this many years ago with telex printers at a limestone quarry where the local ground potential was about 1000v different from the local telephone exchange. tread carefully
If you ever encounter voltage between any to earth spots or any two ground rods ( outside of a few milla-volts ) , then there is something really really wrong. That's when you do the i-inch shuffle with your shoes and get the hell outta there.

This dangerous situation can happen when :
- something looses the common lead/connection/ground , which results in earth ground ( ground rods ) carrying the voltage/load.
- telephone/power poles not having bonded guy wires to earth-ground and to neutral/common/carrier-wire ( never touch any two guy wires at the same time that are on a power pole ).

A few times I have attended some week-long utility power company grounding training classes. You would be surprised what can happen if a home does not have any ground-rods - and the only common ground back to the utility power company is the cable tv coax back to the power pole !!!

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