Yes this is not only possible, but very easy. Just parallel the outputs of your three charge controllers into the battery bank input. This means tie all the positive (+) outputs of your controllers together and connect to battery bank positive (+) input, then tie all the negative (-) outputs of your controllers together and connect to battery bank negative (-) input. Each controller input is then hooked up to a separate solar panel. Hope this helps
I also found some links which may be of some interest:
www.wind-sun.com/ForumVB/showthread.php?t=2858
oupower.com/phpBB2/viewtopic.php?t=1325&...1be633e9169fe723212c