Sorry at everyone! I've connected the U3 at my pc gaming and the hash rate was 62Ghash/s and very stable for all time! The problem was the notebook that went very slow because it has got only 2 Gb of RAM and a dual-core processor. But the current is more than 800 watt!!! So I'll try to build a new computer quad-core with 4-8 Gb of RAM, a power supply of 300 watt max and to connect more antminers U3 with a very big USB hub. This may is the best solution but only during the day because I've the solar panels and I can save much current.