So if I were to undervolt a Gentle Typhoon AP-15 to 9V using a resistor:
One of them draws 0.083A at 12V (confirmed), so its resistance should be ~145Ω. Using a DMM I measured 0.033A at 5V (molex cables swapped), which shows a resistance of ~150Ω. So I'll assume the fan's resistance is between 145-150Ω.
Using a simple voltage divider, I found out that to get 9V to the AP-15 through the 12V rail I would have to put a ~50Ω resistor in series to the fan.
Through measuring with the DMM I also found out that the current draw of the fan also goes down linearly with the voltage, so at 9V the current draw should be around 0.062A, giving us ~0.56W power consumption on the fan.
The power consumption of the resistor would be different though. If I'm correct it should be 3V (the voltage drop) * 0.062A ~= 0.19W. So the ideal resistor should be a 50Ω resistor rated at 1/4W, right?
If I were to connect multiple AP-15s to a single molex connector, I would actually be connecting them in parallel, right? In this case should I use a 50Ω 1/4W resistor in series with each fan, or could I use a single resistor on the 12V node? If the latter is possible/advisable how would I go about calculating what resistor is needed?
Thanks for reading.