I’m looking to redo the networking in my new home. I was fortunate enough to find that all of the phone lines had been run as CAT5e, so my plan is to re-terminate them as RJ45, place a modem/router in the basement where they all originate from, and use wireless APs on each of 3 floors. I think I have a plan in place, but I do not feel comfortable enough in my assessment of PoE to be sure it will work/not be a fire hazard.
So, I plan to use a hex PoE as the router, and use PoE to run three hAP ac² devices from it. The reason I chose the ac² is that I would like to have both wireless and wired capabilities in the locations where they will be (living room entertainment center/office). I do not plan to power any PoE devices from the ac², it will exclusively be devices/PCs with their own power supplies. I am trying to avoid supplying supplemental power to the ac²s, as it will require some ugly power runs or cutting into drywall.
Now, the tricky bit is that I am not sure if am properly understanding PoE/the device specs. Here is the napkin math I have done to validate, but I would very much appreciate if someone can tell me if this is correct/poke holes in my plan:
The hex PoE is powered with the included 24V adapter, which means each PoE output port can supply up to 1A, but a maximum of 2A across all ports. The ac² requires a maximum of 16W with no attachments (I assume “no attachments” means PoE devices, but I am not sure). The ac² can take 18-28V over PoE, so at 24V (assuming it’s the same as supplied by the hex PoE) it will draw 500 mA at the maximum power draw of 16W. This means the hex PoE will be supplying 1.5A total, well within its maximum.
Any flawed assumptions here? I’m especially concerned with the maximum power draw, as the hex PoE would not be able to push 21W to 3 ac² at even 28V. Really trying to avoid making an expensive and/or potentially dangerous mistake. Thanks for any insight you can provide, and I’m also open to any other suggestions regarding my plan.
No attachments in case of hAP ac2 means no usb devices.
The device itself consumes 16W which is 0.666A at 24V (not 0,5A).
So 3 of them will give exactly 48W which is 2A at 24V.
So theoretically this is as much as hEX PoE can provide.
But that doesn’t account for losses on the cables on one hand, and the fact that it is quite unlikely that all 3 hAP ac2 will draw their max at the same time on the other hand.
I think that using 28V power supply (like the one that comes with CRS112-8P-4S) instead of 24V as a precaution is not a bad idea.
Wow, that’s an embarrassing math error, thank you for catching that.
I agree that it would be nice to have a bit of a buffer, but I can’t seem to find that 28V 3.4A supply while browsing MikroTik products. I think it may be a one-off accessory for that specific switch. Do you happen to know if it is sold anywhere? I’m not finding similar products offered elsewhere either,
I am not too worried about maximum power draw/loss, the longest cable run (from the basement to the third floor) shouldn’t be more than 75ft (23m) at most, and it will just be for light Wi-Fi usage from cell phones. Could it be hazardous if there is a power overdraw or will the devices just perform poorly?
Yes, they don’t sell it separately.
There are some 28V ones sold at aliexpress, and also there are options with variable output.
In case of overload it will shut off the power to one of the ports (there is a poe-priority setting to define which one).
I think with a light load and not very long cables you should be good with a default power supply.
At least you can try and see how it goes.
Ok cool, I dug a little deeper and I found a 28V power supply.
I also found MikroTik RBGPOE power injectors, with these I think I should be able to use the power supply that comes with the ac²s to supply PoE. This way, all of my APs should be able to pull up to 0.8A*24V=19.2W in ideal conditions. Besides the extra wiring and cabling in the basement, that should work right? Now, if only I could find them at their recommended price of $8, rather than $20.
Well, of course the injectors will work, but the whole idea of using hEX PoE instead of them is to drop extra power supply bricks, power outlets, cabling, and have an overall cleaner setup (and as a bonus get the ability to power cycle hAP’s remotely if needed).
On the other hand injectors will be cheaper.
So it’s up to you.