3 pins connector voltage ...
 

Voltage we get from the fan connector on a motherboard ( 3 pins ) = 12 v

Am I right ?

Yea, the plus the Rpm signal in the middle en the neg wire.

Although its better to use an molex then hooking your fans up to the mobo.
Some wont boot with a fan connected to the mobo becuase the mobo thinks there isnt a cooler on the cpu.
U can disable this in the bios...