I can do about 30-35 in a row, 50 max with 1 or 2 breaks (couple seconds).
I have no idea how my form is and I have to be pretty well warmed up first.
I did thai boxing and jiu-jitsu for a while before I could do this also.
I also find it easier to count in 5's. If I try to count regular I start to think I'm doing a lot and my mind wants to stop because its a lot. But if i count in 5's (1,2,3,4,5,2,2,3,4,5,3,2,3,4,5...) I mentally don't think I've done as many and can keep going.