I would like to kindly ask you about RB4011 router and cAP ac.
I would use the standard, non WiFi version of RB4011 as a router in the small server room and use the cAP ac access point in like 50m away, the cat6 ethernet cable is already prepared.
My question is: Is it possible to use the passive PoE output on RB4011 to power the cAP ac access point? I would use just a PoE for the access point and if it works, I do not want to use an extra PoE injector, just the RB4011 PoE output.
It would be connected like:
internet input into the RB4011 on SFP port - optical 1gbps
output from the router RB4011 in the passive PoE port - nr. 10
Powering
The device accepts power from the Ethernet port, so you must either use the included passive PoE injector, or
make sure your switch supports passive or 802.3af/at PoE output.
Ethernet port accepts 12-57 V DC 802.3af/at or Passive PoE).
The power consumption under maximum load can reach 13 W.
Connecting to a POE Adapter:
1.Connect the Ethernet cable from the device to the POE port of the POE adapter.
2.Connect an Ethernet cable from your LAN to the LAN port of the POE adapter, please mind arrows for data
and power flow.
3.Connect the power cord to the adapter, and then plug the power cord into a power outlet.
To tell the truth, I did not check the quick guide, just the user manual, which showed just some mounting details. I supposed, that the quick manual has less info, than the user manual, but they both have different details…
The confusing bit for me is that most switches talk Watts not Volts and most are af standard but not af/at?
Cap AC
PoE in 802.3af/at PoE in input Voltage 17-57 V
TP-Link 105PE
Working with IEEE 802.3af compliant PDs, expands home and office network
802.1p/DSCP QoS enable smooth latency-sensitive traffic
Supports PoE Power up to 15.4W for each PoE port
Netgear GS305PE (802.3af) up to 15.4W per port
Dlink GS1005P support the IEEE 802.3af PoE and IEEE 802.3at PoE+ standards, supplying up to 30 W on each PoE port
Also, standard POE doesn’t need to talk about Volts, because it’s always “around 50V” (it differs slightly for each revision). If you see something significantly lower, it’s probably non-standard passive POE. MikroTik devices often combine both.
Edit Disregard (As expected the answers made little practical sense with which to make decisions.
I will have to go elsewhere for information)
Note to dufus self, ensure looking at right switch models (they all have 48vdc power adapters)
To summarize answers by other users (for you only ):
802.3af and 802.3at are similar standards. Both define voltage (nominally that’s 48V) so no need to talk about voltages in this case. And when voltage is fixed, then talking about power (wattage) is same as talking about current (amperes) since relation between the two is linear. However, we’re all used to power consumption expressed in watts, so 802.3af/at device vendors provide this number.
When talking about Mikrotik’s passive PoE things get slightly complicated because devices can take wide range of voltages. The complication comes from the fact that most power supply components are limited according to current (it’s amperes that heat connector, not watts) and in that case it’s technically correct to state maximum current (besides it’s easier to put one number, e.g. 1000mA, instead of a whole table, e.g. 12W@12V, 18W@18V, 24W@24V…).
But then one has to look at supply voltage actually used and multiply that with current limit to calculate allowed PoE out wattage … to be compared to 802.3af/at numbers.
@anav, it’d be interesting if you posted the simplified explanation when you find it elsewhere.
Short answer - yes, your described setup will work just fine.
I agree that it could be a bit challenging if you have to take in account multiple parameters, multiple numbers instead of just one parameter - Power expressed in Watts, but actually it is not a rocket science. As others explained earlier, vendors that write in their datasheets that their, for example, access point supports powering via PoE 802.3af/at, does not write anything about voltages because that means that these devices are purely af/at compliant and that fact speaks about the voltages, maximum power output itself. There is a great table showing the numbers which could not be found in the datasheets I mentioned earlier: https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_implementation
This is the table where the 15.4W comes from which you mentioned for 802.3af device.
I will explain the RB4011iGS+ + cAP ac setup in multiple steps:
Powering of RB4011iGS+.
As stated in the manual:
It could be powered through PoE in (Passive 18-57V) or through DC jack (12-57V).
PoE out capabilities of RB4011iGS+.
Passive PoE (uses the same voltage for output which is received in input - power it with 24V, it will have 24V in output);
Maximum output current 400 mA if input voltage is higher than 30V (max. output power for 48V would be 48x0.4=19.2W), or 600 mA if input voltage is lower than 30V (max. output power for 24V - 24x0.6=14.4W)
Powering of cAP ac.
PoE in 802.3af/at (PoE in voltage range 17-57V). What this says is - if you have a device with 802.3af/at PoE out support, you do not have to think anything. Connect it to your 802.3af/at device and it will power up. The voltage range becomes important if you do not have an 802.3af/at device, as in this case with RB4011iGS+, or if you have only passive PoE injector. So, if you would attach this cAP ac to an 802.3af/at device it will work and everything would be fine. In case of RB4011iGS+ there are some calculations to be done:
a) cAP ac itself (without any load on its ether2 PoE out) could consume up to 13W, or even more if you would use cAP ac to power other devices.
b) As the output power of RB4011iGS+ is already calculated earlier, we need to compare maximum consumption with output power - 13W is less than both 14.4W if RB4011iGS+ is powered with 24V and 19.4W if it is powered with 48V, so this is how you understand that RB4011iGS+ could power cAP ac itself, but this also shows that there could be troubles when trying to power another device from the cAP ac as the power consumption of cAP ac would increase and become higher than maximum power which could be provided by the RB4011iGS+.
So, to sum up, if you are willing to power any of our devices which supports 802.3af/at PoE in and there is also mentioned supported voltage range like 17-57V, you could power it from any 802.3af/at device without any thinking or you should make some calculations similarly like above to understand if you could power this device from any passive PoE out product. But if you have to power some devices from other vendors whose datasheets states that it only supports 802.3af/at or 802.3af, from the wiki page I shared above, you will know that the supported input voltage by these standards would be somewhere between 37-57V (probably some vendors supports a little bit lower voltages, but it should be asked to that vendor directly) and the maximum power consumption should not be higher than ~13W for af or 25.5W for af/at, and again, if you would be willing to power these devices from device supporting PoE out 802.3af/at, you could do it without any thinking, if you would like to power these devices from RB4011iGS+, for example, you would definitely have to use 48V or 57V power supply for the RB4011iGS+ and do the calculations again. As 19.2W@48V is more than 12.95W in case of af, then 802.3af camera, for example, should work just fine when powered from RB4011iGS+. 25.5W in case of 802.3af/at is higher than maximum output power of RB4011iGS+, there could be issues when powering 802.3af/at only device from RB4011iGS+, but in this case also it would be necessary to ask the vendor for maximum power consumption of the device, as it probably consumes less than maximum of 25.5W defined in the standard.
Okay,
I should be clearer, I do not understand how any of the switches can output that kind of voltage on ports??
The standard I get - if it states af it should be able to provide the required output but… how?
Take the TP Link 105PE for example.
Its power supply takes the 60Hz 120V from the wall and converts it for the switch to 9V, 0.6Amps output. (the netgear is 5V, 0.7A)
How does one that magically create 50V outputs on ports??
There is no way it can produce 15W on any port (9V x 0.6amps) = 5.4Watts ???
Hopefully, one can fill in the missing knowledge ( Lost too many brain cells on New Years)!!
I am sure you have mistaken. I did not find, TP Link 105PE datasheet, only PE less version which obviously is not consuming more than 3W. In the datasheet of your mentioned Netgear device, there is information about 48V / 1.25A Power supply. Of course, you cannot get more than 3.5W from a device powered by 5V/0.7A power supply.
Sorry Girts, meant the SG1005P from TP LInk.
You are quite correct its power supply is 48VDC at 1.25amps!!
Which makes much more sense. Same for the Netgear 305P.
I must have been looking at wrong models.
Thanks for your patience!
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