Here's some links:

Overview:

http://www.cisco.com/en/US/prod/collateral/wireless/ps5679/ps8368/product_data_sheet0900aecd8066a16c.html

Installation:

http://www.cisco.com/en/US/docs/wireless/access_point/1520/installation/guide/1520_ch1.html

The following document says 25 Watts typical (~2 amps @ 12VDC) with a Max of 50 Watts (~4 amps @ 12 VDC)

(Quote)

Q. What is the power draw from the Cisco Aironet 1520 Series?

A. The power draw varies with the type of options specified with the Cisco Aironet 1520 Series. Typical power draw is less than 25 watts. Maximum power draw can be up to 50 watts.

(End Quote)

From here:

http://www.cisco.com/en/US/prod/collateral/wireless/ps5679/ps8368/prod_qas0900aecd8066a17b_ns756_Networking_Solutions_Q_and_A.html

Good Luck

Scott