and it has two fans on it i want to add a third in the middle so it will have 3 little fans i was wonding if i would be able to have all three fans under one control of the sentry 2. each channel can handle 10 watts max im not sure of the output.
Also how many watts does a 120mm blue led fan use?
As pyro stated W=IV. Every fan has a voltage and amps written behind it, just multiply the two and you are set (watts= amps*volts; watts = amps^2*resistance). Note that there are fans out there that can consume almost 30-50watts (Delta fans) so be careful not to use those. I have had fans burning out fan controllers because of high wattage but fear not many many consumer fans are well below 5watts. Try to get fans that have good static pressure and cfm, remember most 38mm fans will be higher wattage.