Input Power supply Mikrotik rb133c

Hi sorry for probably not new question, but i use a 20mt abt lan cable with POE to power rb133c and with the power supply furnished by aerial.net (i believe 12v) the board do not boot.
Probably a too long cable ? may i try to use a 18vdc input voltage? is there a DC regulator? what is maximum input voltage that i can power at beginning of lan cable?
many thanks.
Maurizio

http://www.routerboard.com/comparison.html

Hi Equis, many tks for Infos! all OK thanks ciao