I just tried to install Antergos on an old laptop (anyway it was on AC power), the process was slower than usual due to bad connection. I let the process go on, and when I came back to check if it was finished, the PC was in sleep mode, which of course broke the install process. When I restarted the PC on live Antergos, I had a look at gnome-shell energy settings, and it was indeed set to go into sleep mode after 20 minutes. I guess this is not the expected behavior.
Maybe this should be fixed for the next install media?