I’m trying to decide between the RB5009UPr+S+IN and the RB5009GUG+S+IN, and my main doubt revolves around temperature.
I like my network equipment to run cool, so once I have a significant number of devices to power over ethernet, I plan to get a dedicated PoE switch that will act as power source for all of them. That’s because, even if I get the PoE version, I’d rather reserve the “heat budget” of the RB5009 for its own processing, routing and marking tasks, rather than heat it up unnecessarily by powering 6 or 7 devices.
However, considering the small price difference, I’d prefer to get the PoE version anyway just for the convenience of having that option. For instance, in my initial setup I may only have 1 or 2 APs to power up at first, so I may be able to delay buying a PoE switch at all until the rest of devices are installed. It could also come in handy for sporadic ad-hoc testing of other devices.
BUT… this only makes sense if the PoE version (RB5009UPr+S+IN) will run as cool as the non-PoE version (RB5009GUG+S+IN) when NOT used as power source for other devices.
So my question is: Can I expect the PoE version to run just as cool as the non-PoE version when not using its PoE-out capabilities? Or will it always run hotter anyway due to the extra circuitry and components it accomodates?
Specs state a 2 W “base” difference:
RB5009UG+S+IN Max power consumption without attachments 14 W
RB5009UPr+S+IN Max power consumption without attachments 16 W
It doesn’t sound as a lot, even if it can be read as “an increase of almost 15%” it remains 2 W.
How would the power adapter behave?
The first comes with a 24V1.5A power supply suitable for the stated max consumption of 25 W, the second comes with a 48v2A (PoE) power supply that can evidently bear the (unstated) 25/27? W max and has some 70 W available for other devices (but some excess heat production, if any, is moved to where the mains outlet is and in that the PoE power supply is more flexible in placement).
The math is strange, in the second, if max power is 150W and 130 of them can be used for PoE out only 20 W remain (in theory) for the device itself, which is coherent with the 20W of “reserved power” stated for cases of not enough power for the PoE devices and their shutdown based on priority.
So, short of an official response from MikroTik staff, I think it’s safe to assume that the PoE version should be just as cool and efficient as the non-PoE version when not used to power other devices.
Yes, the 2W won’t make a difference in practice, I am more perplexed by the power supply.
The non-Poe one, 24V 1.5A makes 36 Watts, so the 14-25W represent respectively 39% and 70% of the max power the PSU delivers, which should be adequate.
The Poe one, 48V 2A makes 96 Watts, so the 16-27W represent respectively 17% and 28% which are pretty much low values.
It is clear that Mikrotik has chosen a compromise in the second (enough to power a few PoE devices, but not capable to deliver the whole 150W the device can bear) probably because a beefier PSU would be much less efficient with even lower pencentages of load.
On the other hand, generally speaking, it should be preferrable to use higher voltage (which means automatically less current) as dispersion and generated heat should be less.
Probably, but it will have to be seen, a 48V 0.8 or 1 A would be a better choice in the long run if you don’t use the PoE option.
So from a PSU perspective, it would probably be more efficient to run maybe 1 or 2 PoE devices off the RB5009, so that the PSU is running closer to 50% load, and leave the rest to feed off a separate PoE switch. Assuming, of course, that the switch’s PSU is also operating at around 50% load when powering those remaining devices.
But from a router perspective, though, it is of course better to avoid feeding any PoE devices off it at all. Because that puts extra heat on the router itself, which might limit its actual performance under high load. So like you said, it would probably be best to get a different PSU and avoid using it as PoE source in the long run.
I assume something like this would be suitable for the task?
Yes, though personally I prefer the “other” style for PSU’s with the “brick” connected to mains through a cable as it gives more freedom to place it where you want instead of having it sticking out of the mains outlet.
Mikrotik used to have a POW48 with 48V 0.8A that would be IMHO ideal (I think it still can be found online in some shops), the new one is 48POW 1.5A which is already too much.
But there is no need for it to be necessarily Mikrotik, it’s a simple (passive) power supply.
Yep, agreed. Also prefer the other format, as I would keep this in a closet with other equipment and the power strip sockets will get easily blocked by this kind of PSUs.
When one uses power adapter only to power router (i.e. no PoE-out), then it’s better to use PA which outputs lower voltage (but still equal or higher than lowest acceptable input voltage). The reason: router’s electronic parts require pretty low voltages (probably anything between 1.8V and 5V), so there is one (or multipke, even multi-stage) DC-DC downconverters. Efficiency of typical DC-DC downconverters is inversely proportional to difference between input and output voltage, so down-converter to e.g. 3.3V will operate more efficiently if input voltage is 18V than if input voltage is 48V.
The (in)efficiency is overwhelmed by cable loss when using PoE with lower voltages (over long cable sections), so when using same PA for PoE-out, it’s better to use higher voltages (if it’ selectable at all, 802.3 af/at requires 48+V power adapter).
Yes, in theory you are right, but it depends on a number of factors, load characteristics, amperes needed, the way the DC-DC converter has been designed, the frequency it operates and what not, typically, in practice, in a properly designed converter the difference in efficiency may be in a few % over the proper range, like (say) from 94% peak to 88% or so.
The fact that the good Mikrotik engineers gave prevalence/priority to the higher voltage may (or may not) be connected.
Anyway using the 24V 1.5A power supply that comes with the “normal” RB5009 is a very good idea.
Very good, so we have a real life data point, thanks .
So, it is (approximately) the 2W difference stated in specs between the non-Poe and the PoE one?
Or is it a coincidence?
I mean, also the non-PoE version can be powered with 24-57V, so the 2W difference could be due to the non-PoE version being tested @24V?
The way I read post by @andkar … it’s the same device (PoE version) powered either by 24V or 48V. So the difference is efficiency in downconverters … and possibly some 802.3af/at specific PoE circuitry which may get switched off when device is powered with 24V (and can thus not provide 802.3af/at PoE). This possibility would be ruled out (or confirmed) if same test was done using the non-PoE version.
And I doubt that MT engineers opted for higher supply voltage considering internal reasons, I strongly believe it’s due to PoE out (either passive or even 82.3af/at which requires 48V or higher).
But you’re right about range in efficiency of downconverters, most really do operate between around 85% and 97%. Now whether the difference is insignificant or not can be pretty subjective, but if there aren’t any other constraints regarding supply voltage, I’d say this consideration can (and should) be relevant as to PA selection.
If the PoE version is powered with its stock 48V PSU, it uses 2-2,5W more idle power than the non-PoE version.
If the PoE version is powered with the 24V PSU, it probably uses the same power as the non-PoE version.
We would need to test them side by side to confirm. But I assume it’s also likely that, using the 24V PSU, the operating temperature of PoE version will largely be the same as that of the non-PoE version, except maybe for any reduced airflow that may be caused by whatever extra PoE components it’s housing inside its case.
@VMX
Until this is confirmed by further tests, either:
the PoE and not PoE versions are essentially the same BUT the power declared in the specs is for the first relative to 48V (or so) and for the second relative to 24V (and it is the 2W difference)
or:
the PoE and not PoE versions are different internally and the PoE version does consume 2W more at the same 24V
If a) the total difference is 2W
If b) the total difference could be 4W
In both cases, I don’t think it would make much of a difference from the point of view of thermal management, 4W is a lot in percentage, but it remains 4W in absolute terms.
I put in my first RB5009UP last week and got my ass handed to me.
The POE on the RB5009UP is cutting on and off serving 3 Access Points that TOP out at 13 watts each. https://mikrotik.com/product/48v2a96w is the included Power Supply
SO lets assume MAX POWER 13x3= 39 watts.
Mikrotik says that each port can do 20 watts. Tech support even confirmed this.
However… I am now having to buy a CSS610-8P to drive these guys. Didn’t plan for that $220
Wow, not good! If those 3 APs are too much for the RB5009, my 2 APs might be as well… might have to reconsider and get the non-PoE version + a PoE switch from the start.
Out of curiosity, why the CSS610-8P and not, say, the RB260GSP? Were you planning to power half of the devices with the RB5009’s and the other half with a smaller switch, and now you need a bigger switch that can feed 8 PoE devices?
Only to keep things as together as possible, gotspring’s misadventure with a RB5009 is posted here: http://forum.mikrotik.com/t/rb5009upr-s-in-power-problems/174073/11
though it is not (yet) clear whether the power supply or the RB5009 unit he tested can be defective.
Even if Mikrotik’s way to deal with PoE specifications appears more often then not “vague”, I don’t think that when they declare 150W for the router and 96W for the power supply a setup with only 40W+25W=65W can fail, if all the devices involved function correctly, it would be - more than deceiving advertising - a fraud.
It seems that the declared 802.3at support by Mikrotik is not fully-fully compliant with the standard, but at least in theory the 13W or so access points are well within the 15.4W of the 802.3af specs, so it cannot be an issue with negotiation between 802.3af and 802.3at power requirements.
Since the RB5009 model that supports PoE is a relatively new device there are not many reports on the field, let’s wait and see if there are new similar reports of the standard setup being so much underpowered.
.