HELP - resistors and dip-switch

[audioguru2]

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?

 

[allvol]

Hello Virus, with Audioguru and others,

I've looked into this noise matter even to the extent of doing several breadboard versions.

 

[audioguru2]

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.

 

[allvol]

Virus,

Re: your reply #62

Could you be expecting too much?

 

[Virus]

Guys

By 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

 

[audioguru2]

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.