Death's Hand - Not generating power charges?

Not sure how that mechanic works. 30% chance to get a power charge on stun, but I'm not getting any whatsoever. Maybe I'm not doing enough damage per hit, but I can't see that happening as I kill things in like 2 hits with my crit Bino's reave build. Maybe they die too fast to be stunned? I'm using reave and my dps is about 30k

Edit: If I run Dried Lake, it works... so maybe I don't do enough per hit for higher level maps, because the map I was trying it on was a T5