I'm having trouble getting proper tension on a BB30 eccentric bottom bracket with a 1/8 x 1/2 inch chain running to an Alfine IGH. First I left enough slack to rotate the BB shell as far forward as possible (if the shell were a clock, this would be 3:00).

A little slack, but that was fine until winter hit; now I'm riding over some pretty rough terrain at times, and twice today I bounced the chain off the ring while riding over really bumpy ice.

So I try to remove a link and tighten up. But when I remove a link, the chain tightens so far so as to create an unrideable amount of tension/friction, even when the BB shell is rotated as far back as it will go (9:00).

This seems like some BS (why would someone design a tensioning system that won't accommodate a 1/2 inch chain?), but I think that maybe I can fix it by changing the chainring/cog combo. So I switch out the chainring from 40t to 38t (cog is 19t).

No change. I mean, now the chain has gone super slack with the BB in the 9:00 position. So I rotate to 3:00, and I've got the same amount of slack as when I first started. Remove a link, and again it's too tight to run even with the BB at 9:00.

*sigh* I miss my sliding dropouts. But I want the frame with the EBB to work with the IGH. Am I missing something? Any ideas?

I don't know the spec of your EBB, but some of that stuff ALSO require a half-link to do the job.

You need to remove one link and add a half-link.
1 1/8 half links are pretty easy to find, they are std BMX parts.

Thanks, I'll give that a try.