concurrent writing

I have always had bits of new books appearing in my head when I am a long way short of finishing a current work. In the past I've either done nothing about them or started up notes in little exercise books that now litter my desk. Lately I'm starting to create files with rough chapters in them coinciding with what's coming to me. It would be great to write 2 or 3 books simultaneously but I'm not sure I'm capable of doing so. I think I would end up with the same voice in all three works and would probably mix up the names. At the moment I have a stand alone hammering at me; bits of a new series; I am working on my first ebook duology and my angel series is languishing at 1 and 3/4 books or 3 and 3/4 books if I split them for epublications. Of course, getting bits of a story is by no means the whole lot - so heaps of work to do.