dcc locomtives

I have small double loop n scale layout with turnouts connecting the two loops. I just finished wiring the layout for DCC, and when i run one locomotive, everything works flawlessly, but when i add a second locomotive, they work briefly, then the entire layout loses power. Any insight as to...

Has anyone any experience converting an Athearn F7 to DCC? I have a full passenger set with a pair of Athearn F7s (one powered, one dummy) and I'd like to use it with the DCC setup we're using now.