Thinking about going to Radio Shack...or "The Shack" as it is now going to be called, to get some resistors, and make some of my case fans a bit quieter. Which resistor should I use? Also do I just place it inline with the red power wire from the case fan right? I'm good at soldering, so I'll probably just solder it after I test out the resistor.
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Using inline resistor to quiet fans
- Thread starter PS3
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i know you used to get adapters that would kick fans down to 5v and 7v which were nothing but resistor and shrink tube but keep in mind they get freaking HOT, im assuming the more they are resisting the hotter they get but i had some 5v adapters and i wouldn't want them up against anything that could melt 
Fans normally run on 12V (yellow + black), you can often get the desired result running them either on 7V (yellow + red) or 5V (red + black), without needing to burn extra power in a resistor. If you do end up needing a resistor, you'll probably just have to experiment since it depends on your needs and your fans. Probably you'd want something in the 50-500 ohm range, you'll have to experiment. Don't get anything smaller than 1W resistor, especially if you're dropping a lot of voltage on them - they will get hot and could be a fire hazard if you get small 1/4 or 1/8W ones - you could easily need to drop a couple W.
There's no such thing.
Voltage loss to resistor depends on current going through it (U=IR) and current depends also on fan which isn't exactly linear, plain resistive load.
(but zeners could be used for dropping voltage known amount)
Totalchaos
Limp Gawd
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google is your friend
Arcygenical
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Those adapters drop *normal* specced fans down to *about* 5-9v, depending on the manufacturer's resistor rating.
So... they very much do exist, but the actual output voltage the fan sees is different for every fan.
Wouldn't wrapping electrical tape around the resistors negate such a hazard? I mean they can't get that hot could they? The extra power burned in a few resistors to slow down fans should be negligible I would guess. Well I'll post the resistors I end up using.
Just advising against using 1/4W (basically the 'standard' size for through hole) or smaller resistors for this. At a guess you're going to be dumping at least 0.5W, probably closer to 1W into the resistor (if you have a multimeter you can measure the voltage drop across it and the current through it to calculate P=IV). If you use a 1/4W resistor here it will probably get hot enough to burn you pretty badly, though maybe not start a fire. I wouldn't put tape around it, that'll just insulate it and make it get even hotter.
FWIW it's easy to literally explode resistors by applying too much power, and I've seen them glow red hot when misused. They can certainly start a fire (consider that an electric heater, toaster, stove etc. is basically just a big power resistor), though obviously this isn't going to happen if you use values useful for what you're trying to do.
electrical tape will just turn to mush from the heat, best bet is to solder it in and shrink tube it and make sure it isnt on anything that can melt, i don't know how hot they get but i know the one i had used ages ago i couldn't touch
i've used these resisitors in the past with 120mm fans and have never noticed ay heat issues. be aware, some fans are touchy at startup and the blades may not begin spinning at a voltage less than 7-9v. the fan LED will light, but the blades won't spin. you will need to test this.
Gorankar
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That, and as fans get older, that problem only increases.
krameriffic
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It seems unlikely that he would want to exercise his degree in EE designing a more complex circuit for power control while he could buy a fan controller for $20.
im no electrical guru but i have a hand full of these in my drawer
Yes I had a number of these "ready-made" resistor cables as well. Had 7v and 5v versions and switched between them depending on the speed I wanted. These might be better if you want to avoid soldering.
Very useful if you're building a small mini-ATX system and space is at a premium and you want to avoid a traditional fan controller.
Used a 1/2 watt 47-ohm resistor at THE SHACK: Part # 271-1105. Cost .99 for a 5 pack. I let it run for a while and the resistor didn't get hot...just a tad warm I guess, nothing to be concerned about. Reduced noise drastically on the yate loon ds12sl. PC is finally next to silent. I must say, usually the yate loon low rpm fans are quiet, but for some reason, the one I was using was a bit loud for the low rpm model. Fan still pushed adequate air after putting the resistor in. If you are using the low rpm yate loons, take note, this works great, and you can quiet 5 fans for a buck.
Running resistors in parallel will reduce the current going through each one so they don't get as hot. It lets you use the common 1/4W ones. You would need higher value resistors though. For each one added you multiple the value you needed. To get 47 ohms you would need 4 of whatever standard is close to 188 ohms. Last week I bought a handful of 2W resistors for $1 each, they're probably less bulk than many resistors in parallel. Not sure what I'll use most of them for, I just like buying components. Maybe I can make some adapters for fans and sell them on these forums.
You mean serial.
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you can do either. running two in parrallel means you have to get two that are twice as resistive as the actual resistance you need.
running two in serial means you have to get two that are half as resistive as the resistance you need. Either way the load will be split on two
I've done this mod on two standard 80mm case fans, spread across three resistors parrallel . I don't remember the actual resistance or voltage drop i had, but i can tell you the resistors all got pretty hot.
edit: from my general knowledge of how hot heatsinks and cpu's are, to the touch i'd say they felt around 60 celcius.