PWM fan speed controller killed my PC - Page 1
Forum section: electronics / beginners

author: OutbackBob
author_rank: Contributor
timestamp: April 19, 2015, 04:54:20 am
content: Hey All,I just built up a PWM fan spped controller for my PCs GPU fan and it worked just fine for about 8 hours, until one of my HDDs failed and corrupted all data on the other 2.I'm pretty sure its the controller thats the culprit because as soon as I unplugged it the failed drive detected again and started working.I built it up as per this:http://img.techpowerup.org/100617/fancontroller.pngInstead of driving the transistor, I put the PWM output straight in to the PWM line of my fan. I also used a 74HC14 instead of the 74AC14 as it was all I could get at Jaycar.My question is, why would this cause my HDD to fail? I hooked it up using the PCs +5v and +12V rails, so could it be causing ground issues or causing those rails to drop out of spec somehow?Want to learn from this mistake as it's been a costly one (in time anyway).Thanks.

author: poot36
author_rank: Frequent Contributor
timestamp: April 19, 2015, 06:55:37 am
content: If you have a oscilloscope take a look at the 5V line on the hard drive with and with out the fan controler connected as well as the output to the fan. You can also try your multimeter on ac to see if there is increased ripple when the circuit is connected. I would try building the circuit as described and see if there are any problems. I suspect that high frequency noise is been coupled into the power rails by that circuit. Also without the transistor the output could potentialey be swinging below ground and creating more problems and potential damage to the fan circuit board as well. I have measured with a 100 Mhz scope on the 12V cpu power connector switching spikes of 25V or so so if that somehow coupled into the 5V line through your modifyed circuit that could explain the problem. You could also try placing a 100µF 10V minimum rated cap across the fan controlers logic chip as well as a 100nF cap for the high frequencys and see if that fixes the problem. The cap values are approximate.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 19, 2015, 07:15:39 am
content: clamp the fan cable with votage suppression diode, inductance spike during switch off is 90% the cause of the trouble.

author: Ian.M
author_rank: Super Contributor
timestamp: April 19, 2015, 07:34:03 am
content: The fan is designed to be PWMed and the 74HC14 should have been an insignificant load on the PSU 5V rail so it points to either a PSU that was running right on the edge of overload before the controller was added, or a PSU that is failing, or moving cables around during fitting partially blocked airflow to the drive bay resulting in an overheated drive.

author: OutbackBob
author_rank: Contributor
timestamp: April 19, 2015, 07:57:36 am
content: See attached screenshots of 5 and 12 volt rails both before and after I plugged my device in.It was no where near as clean as I was expecting. At one stage without my device plugged in I was seeing almost 4Vpp. Nothing conclusive in there to point the finger at the speed controller (to my untrained eye anyway).Quote from: Mechatrommer on April 19, 2015, 07:15:39 amWould this not be built in to the fan already? It is a 4 wire fan designed to be PWM controlled.

author: Seekonk
author_rank: Super Contributor
timestamp: April 19, 2015, 08:19:08 am
content: I've never seen a four wire fan before. Could you point to some data on this? I see no temperature control on this. Do you just adjust it to a pleasing sound level and let the electronics burn up? Looks like you selected a fan controller at random off the net that wasn't even designed for your fan.

author: Monkeh
author_rank: Super Contributor
timestamp: April 19, 2015, 08:25:35 am
content: Quote from: Seekonk on April 19, 2015, 08:19:08 amhttp://formfactors.org/developer%5Cspecs%5C4_Wire_PWM_Spec.pdfYou really should open a PC every now and then..

author: OutbackBob
author_rank: Contributor
timestamp: April 19, 2015, 08:32:56 am
content: I'm using a standard intel 4 wire CPU cooling fan on my GPU as the stock fan died.You are correct, no temp sensor. I just have the knob out the front of the case and turn it down when browsing the web and up when playing gamesI thought a fan controller would be a quick fun little project to build up as I am still very new to the world of electronics, didn't realise I was risking my computer!Good news is, just finished re-installing with Windows 10 and all data on my other drive looks to be okay.

author: wraper
author_rank: Unknown
timestamp: April 19, 2015, 08:42:21 am
content: Quote from: Ian.M on April 19, 2015, 07:34:03 amNo it is not designed to be PWMed.(4 wire fan can be driven directly, but schematic attached is incorrect). Usually there is also internal electrolytic capacitor across the power wires. You can only make a linear regulator or DC/DC converter with an inductor to regulate the speed of it. Those stupid schematics with PWMing the fan directly is a way for trouble.EDIT: Didn't read thoroughly. Of course 4 wire fan can be PWMed directly. But schematic taken as reference is still stupid.

author: Zero999
author_rank: Super Contributor
timestamp: April 19, 2015, 08:49:23 am
content: He said it's a four wire fan which is designed to be controlled via PWM. The output of the oscillator is connected to the fan's PWM input, rather than the power supply.The only problem I can see is the PWM frequency is too low. I calculate, it'll be in the region of 2.5kHz but the document linked to above says it should be between 21kHz and 28kHz but that shouldn't cause problems with the hard drive.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 19, 2015, 09:11:02 am
content: Quote from: Monkeh on April 19, 2015, 08:25:35 ambut the sch in OP shows 2 wires and a good fat low side switching NPN. does that mean output3 of 74ac14 is driving 4 NPNs?

author: Ian.M
author_rank: Super Contributor
timestamp: April 19, 2015, 09:48:13 am
content: Quote from: OutbackBob on April 19, 2015, 07:57:36 amThat's pointing at a failing PSU. If the PSU is the same age as the rest of the machine (which we know is old enough to be on its second GPU fan), its quite likely that its output smoothing caps are pretty tired and have less capacitance and a higher ESR than they are supposed to.Fitting a new, good quality PSU would be a good idea, as although PSUs normally die quietly, I have seen several that fried the motherboard and all drives and cards by catastrophic loss of regulation when they died.

author: Zero999
author_rank: Super Contributor
timestamp: April 19, 2015, 10:07:18 am
content: Quote from: Mechatrommer on April 19, 2015, 09:11:02 amBut he then said:Quote from: OutbackBob on April 19, 2015, 04:54:20 amQuote from: OutbackBob on April 19, 2015, 07:57:36 amFor clarity he should've changed the schematic.Quote from: Ian.M on April 19, 2015, 09:48:13 amYes, it's most likely a bad PSU and this was a coincidence.

author: Seekonk
author_rank: Super Contributor
timestamp: April 19, 2015, 01:51:00 pm
content: I open up plenty of PC's, but only to destroy them for parts. 4 wire units haven't hit the skids yet.

author: BradC
author_rank: Super Contributor
timestamp: April 19, 2015, 02:57:53 pm
content: Quote from: Seekonk on April 19, 2015, 01:51:00 pmI can send you one. I had a "coolermaster" 4 wire CPU fan seize a bearing a week ago and tried very hard to destroy the remainder of the machine. Has been replaced with a fixed speed Sunon with real bearings.

author: Monkeh
author_rank: Super Contributor
timestamp: April 19, 2015, 05:58:10 pm
content: Quote from: Seekonk on April 19, 2015, 01:51:00 pmYou haven't scrapped any crappy P4s? Things must be desperate in your area.