I've searched the web for some sort of resistor calculator, and have not been able to help my self. Simply put, I'd like to add resistors to some of my fans, using 3 pin mobo connections (for cable management). I need to know what size resistor would I need to run a 12V fan at 7V. I'm not sure what other figures are neccesarry for this calculation, but if someone would help me with a formula, I would greatly appreciate it.
Google Ohm's law. I always forget the correct formula. I want to say 56ohm 2 to 5 watt, but I'm not doing the math, just pulling vague numbers out of my memory hole.
Don't lie, we all know V=IR, that one is easy... right? The correct resistor depends on the resistance of the fan, so you'd want to know accurate specs of the fan to be able to figure out what value resistor you'd need. A 56ohm may run one fan at 7v, but another fan may run at 10v, etc.. I like to just whack a couple of diodes if i want to slow a fan down. Each diode will drop about .7 volt, or use germanium for ~.3v drop, but that's getting really fussy! You can use a zener diode aswell for larger drops, like from 12 down to 7, just make sure the wattage of the zener is plenty for the job.
Quite simple. The fan may tell you outright how much current it draws, but if not use Ohm's law (mentioned above) to calculate the current draw using the DC resistance across the coil of the fan and the voltage applied from the 3-pin connector. From there you take that same value for current, plug in 7 volts, and then solve for the value of the resistor to put in series with the fan. The value you get will be the resistor value alone, not the series combination of the fan coil and the resistor.
Try words like 'fan speed resistor calculator' in your search. First link. It's not an accurate way to slow fans down. Better ways.
Rheostats, and any sort of bay bus presents some cable management issues (unnecessarrily). I like the simple, permanent method of adding a resistor to get the desired speed, wich would be directly influenced by noise. I've ordered some new fans that will be in next week. So, if they are any bit as noisy as the Lian Li fans, I'm book marking the pages you guys helped with and will refer to them. Thanks. cpemma, guess google only helps you find it, if you know what you're looking for!
