SilverStone SST-ST1200 PSU whistling sound - Page 1
Forum section: electronics / repair

author: m4rtin
author_rank: Regular Contributor
timestamp: May 13, 2016, 09:59:14 pm
content: I have aSilverStone SST-ST1200PSU which seems to control fan rotations according to PSU load/temperature. Usually the fan does not rotate at all and PSU is completely silent. Sometimes the fan rotates slowly and PSU is again almost completely silent. However, quite often it looks like PSU fan has not enough power to start rotating and then the PSU makes an annoyingwhistling sound. When I very gently push the fan, it starts rotating slowly and then the PSU is again almost completely silent. What might cause this behavior?

author: TheMG
author_rank: Frequent Contributor
timestamp: May 14, 2016, 12:31:16 am
content: They're probably using PWM to control the fan speed. At very low duty cycles the available torque to the fan motor is not enough to overcome the initial friction and get it actually spinning. The sound you're hearing is the PWM frequency as it causes the motor to vibrate a bit.As the PSU warms up a bit more and the PWM duty cycle increases eventually it will get spinning, so its nothing to be overly concerned about.This is why some designers have the fan controller initially turn the fan on at 100% speed for a second, and then ramp it down to the desired lower speed. This is to ensure there is enough initial torque to get the motor spinning. Obviously SilverStone must not have used this technique in their PSU design, probably to try to keep noise to a minimum.

author: m4rtin
author_rank: Regular Contributor
timestamp: May 14, 2016, 02:25:03 pm
content: Quote from: TheMG on May 14, 2016, 12:31:16 amAs this is a two-wire(12V DC and GND)Young Lin DFS132512Hfan, then I guess, that PWM is done in PSU PCB while modern 4-wire fans support PWD input signal and thus control the rotation speed itself?Quote from: TheMG on May 14, 2016, 12:31:16 amSo the whistling sound is made by vibrating fan?Quote from: TheMG on May 14, 2016, 12:31:16 amThe problem is, that sometimes this takes a very long period of time and as this high-frequency whistling sound is very annoying, I usually end up helping the fan with a hand. However, after some time the fan stops and then tries to spin again and the whole thing repeats. I guess one option is to swap the current fan for a smaller one. Then the fan would rotate more often, but at least it's probably able to overcome the initial friction when it wants to rotate. Are there any other options?

author: TheMG
author_rank: Frequent Contributor
timestamp: May 14, 2016, 04:32:02 pm
content: Quote from: m4rtin on May 14, 2016, 02:25:03 pmThat's probably what is going on.Couple of options, you could try adding a simple R-C circuit to try to smooth out the power going to the fan.Or even simpler, wire the fan directly to the output of the power supply so it's always running.

author: m4rtin
author_rank: Regular Contributor
timestamp: May 23, 2016, 09:53:05 pm
content: Quote from: TheMG on May 14, 2016, 04:32:02 pmI uploaded avideowhere one can clearly hear this noise. Did I understand correctly that this is caused by motor inside the fan moving very quickly back and forth, i.e vibrating?I tried thisYoung Lin DFS132512Hfan with both 5V and 3.3V. With 5V the fan was a bit too noisy, but with 3.3V it was almost silent while there was I would say decent amount of airflow. However, if possible, then for learning purposes I would like to try to build the RC circuit at first. Maybe it will help. Am I correct that capacitor essentially smoothens the current to the fan? I mean instead of current with the following characteristics(because of PWM):..the fan receives current with following characteristics:Last but not least, why is the resistor needed?