audioguru Posted May 31, 2006 Report Share Posted May 31, 2006 I have a permanent magnet electric motor operating its PWM at about 3kHz and it whines loudly.If your motor has a high inductance then a low frequency should be used. It takes time for current to build up in an inductor. Quote Link to comment Share on other sites More sharing options...
allvol Posted June 1, 2006 Report Share Posted June 1, 2006 Hi All,I'm back, and humbly apolegetic. Quote Link to comment Share on other sites More sharing options...
Virus Posted June 1, 2006 Author Report Share Posted June 1, 2006 AllvolHow was your golf day?Thanks for the links, interesting info.The best I can describe for you what I want to do is, if it is at all possible for you to build the circuit in Rely 14, 3 components only.You can adjust the trim pot for the fans to come to a dead stop when your PC is cold, just switched on, with the thermistor in place close to the CPU heatsink, ( by playing around until you get a good position for the thermistor) it will easily control the fans from 0 % to Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 1, 2006 Report Share Posted June 1, 2006 The circuit with only 3 parts has the Mosfet as a resistor and it gets hot. The Mosfet in a PWM circuit doesn't get hot. The difference in the cost of the parts is nearly nothing, but the simple circuit needs a big expensive heatsink. Quote Link to comment Share on other sites More sharing options...
allvol Posted June 1, 2006 Report Share Posted June 1, 2006 So . . .. Quote Link to comment Share on other sites More sharing options...
Virus Posted June 1, 2006 Author Report Share Posted June 1, 2006 audioguru / allvolI have built (bread boarded) about Quote Link to comment Share on other sites More sharing options...
allvol Posted June 1, 2006 Report Share Posted June 1, 2006 Well, Virus, I don't know what to say. Quote Link to comment Share on other sites More sharing options...
Virus Posted June 2, 2006 Author Report Share Posted June 2, 2006 allvolImagine working on your PC and you have this constant whispering in your ears.Not practical. Is there a solution ? Much higher frequency mabe.?HELP MAN HELP !Virus Quote Link to comment Share on other sites More sharing options...
allvol Posted June 2, 2006 Report Share Posted June 2, 2006 GM, VirusFrom the 4QD website: In a practical low voltage controller the switch opens and closes at 20kHz (20 thousand times per second). This is far too fast for the poor old motor to even realise it is being switched on and off: it thinks it is being fed from a pure d.c. voltage. It is also a frequency above the audible range so any noise emitted by the motor will be inaudible. It is also slow enough that MOSFETs can easily switch at this frequency. Measure the frequency at pin 3 of your 555 without the thermistor in circuit. Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 2, 2006 Report Share Posted June 2, 2006 In a practical low voltage controller the switch opens and closes at 20kHz (20 thousand times per second). This is far too fast for the poor old motor to even realise it is being switched on and off: it thinks it is being fed from a pure d.c. voltage.Doesn't the inductance of the motor reduce its max current at the higher frequency? Quote Link to comment Share on other sites More sharing options...
allvol Posted June 3, 2006 Report Share Posted June 3, 2006 Hello Virus, with Audioguru and others,I've looked into this noise matter even to the extent of doing several breadboard versions. Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 3, 2006 Report Share Posted June 3, 2006 If your fan sounds like a dentist's drill then the frequency of the 555 is too low and is audible. Reduce the value of its timing capacitor.Electric golf carts and wheelchairs don't make a whining noise because their PWM operates at a frequency above what you can hear. Quote Link to comment Share on other sites More sharing options...
allvol Posted June 4, 2006 Report Share Posted June 4, 2006 Virus,Re: your reply #62Could you be expecting too much? Quote Link to comment Share on other sites More sharing options...
Virus Posted June 4, 2006 Author Report Share Posted June 4, 2006 GuysBy whisper I meant irritable, nagging, down warring sound, doesn’t mater how soft it is it will catch on to you. I will accept a whisper any day.What the use of trying to get rid of the fan noise, and replacing it with electronic noises.Can PWM on a 12v case fan’s, be quiet enough, to be used in this task, or should I stick with the original diagram (reply no 14).There’s got to be a way.Virus Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 4, 2006 Report Share Posted June 4, 2006 You can use the fan's driving transistor as a completely quiet variable resistor, then it gets hot.You can use PWM at a frequency above 20kHz so it is completely quiet, and it doesn't get hot.You can use a bigger fan that can turn slower to move as much air as a smaller fan running faster, and the noise will be much less. Quote Link to comment Share on other sites More sharing options...
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