Bob and Gilly have you headed in the right direction with a separate DC supply to operate the relays . Bob also has the right idea with the relay selection. Those are rated for 10A and will work well for this application. I am using two 8 bank relay sets as I am powering 9 roundhouse bays and 7 whisker tracks around my turntable. My setup differs a bit as I also incorporated some additional 555 relays to activate the watch dog signal for DCS. Here a pic of my setup.