Power Adapter Barrel Size for PoE

ahpsi wrote:

I would note I have had great success powering many different devices from POE / High POE using an appropriate injector at the head end and splitter at the device end. In the case of the ReadyNAS Ultra/2 the power requirements as listed here -> http://www.readynas.com/?page_id=3962#TechnicalSpecifications note 35W typical with two 2TB drives. If you use a 4 pair high POE injector -> http://www2.microsemi.com/PowerDsine/Documentation/DataSheets/PD-9501G.pdf and a high power 4 pair splitter providing 12V -> http://www2.microsemi.com/PowerDsine/Documentation/Datasheets/PoE_951_Splitters.pdf you still have 19W (allowing for heat dissipation in the cable) of headroom (in case drive and fan spinup or boot draw more). By the numbers that setup should work- the supplied PS is rated at 2.5A@12V and the 4 pair splitter is rated at 2.5A@12V. The eBay item listed is a passive device that I could not recommend as low DC voltages do not survive long cable runs as well as higher voltages, hence the active splitter taking 50V-57V down to 12V. Of course from a cost perspective the active POE devices I've linked are much higher and probably not worth the expense - unless you already had a multiport injector and really needed the closet to be POE powered only.

My concern here is that the 35W is typical, not worst-case - and as you indicate you need to account for cable losses. I think there is some risk that there might not be enough available power at times, and I am not sure how the NAS would deal with that. So I wouldn't personally use it for the NAS, particularly since without more people else saying that they have successfully the power system with their ReadyNAS.