Voltage drops when turn on electric fan

My voltage drops from 14-15 to 12 when I turn on my newly installed elec. fan. I did not use the thermocoupler with relays due to confined space. I ran my power source straight off the battery to starter post using 12 gauge wire with 30 amp fuses and 30 amp switches on both speeds. Both speeds pull 11 amps at the fuse. I am using a 140 amp powermaster alt with upgraded to 8 gauge wire back to the solenoid and a 10 gauge ground from alt to frame. With both speeds on I get 12 volts at the alt. I did the total rpm speed at the alt using powermasters calculations and get 16,700 not to exceed max of 18,000. Is it a must that I use the thermocoupler with relays? It does use 30 amp fuses also but much bigger in size. Thoughts appricated!