The maximum number of fans that can be connected to the NA-FC1 is limited by the total combined power draw of all fans, which must not exceed 3A for 5V and 12V fans. In addition, please keep in mind that there may be lower limits imposed by the power source (e.g. 1A max. for most motherboard fan headers, max. 0.5A max. for USB 2 ports, etc.). However, as the NA-FC1 only passes through the power and regulates fan speed via PWM rather than voltage control, these limits are not related to the NA-FC1 as such.