AP 55 POE Question

Question

I am looking to rollout some AP55s and have come across a strange situation. 
 Our CISCO (2960S) switches are rated sufficient to support the power requirements of the AP. 
 Sure enough, when patched in, I got a green blinking light. 
 I then left it unplugged for a couple of days and when I patched this in again in the same location, I got no light. 
 Once I attached a POE injector, the AP came to life. 
 After a few hours, I removed the injector and patched it back to the same cable and now all is well. 
 It is almost as if need a charge boost of some sort. 
 Just wanted to know if anyone has come accross this before and if anyone can recommend a 12volt power supply that will work for the AP55 as Sophos does not sell any directly.

Aditya Patel · Answer

HI Chris, 
 You may as well install POE- compliant Switches in your network is you have several AP and wish to use them without using POE adapter on each site. or you may use a POE adapter when required . 
 It would occur that the device would consume 11W to 13 W of power and practically this is possible on POE compliant switches. But there is a Downside, Power Dissipates by using a Long Cable and the loss in between say 10% approx on Copper . To be a specific check the loss you may calculate P (rated)=VI(Rated)-VI(loss) , where P(rated) is the power output from the Switch and P(actual) is the power output from the other end of the cable. 
 I would advise POE+ Compliant Switches which would deliver 24W output and as POE would deliver 14.5W. (Without loss (rated value)).