Question about PWM Controller for some brushless DC fans.

[xReM1x]

Hi! I need a PWM Controller to control some PWM computer fans. (my most powerful fan need around 4.80A at the start and 4A normal.) So i tought about this one : **broken link removed** will this one work? I put 12VDC and i can control the duty cycle with the pontiometer?

 

[chuckey]

" PWM computer fans. ", I do not understand this. Most BLDC motors have a chip inside them and sensors to control when the current is switched into which coil. When the fan is actuated, the oscillator starts up to "catch" the rotor it then speeds up to accelerate the motor to its operating speed. This unit switches the 12V on and off at a high frequency, the on/off ratio can be varied to give a different mean DC output. I cannot see it working.
Frank

 

[xReM1x]

" PWM computer fans. ", I do not understand this. Most BLDC motors have a chip inside them and sensors to control when the current is switched into which coil. When the fan is actuated, the oscillator starts up to "catch" the rotor it then speeds up to accelerate the motor to its operating speed. This unit switches the 12V on and off at a high frequency, the on/off ratio can be varied to give a different mean DC output. I cannot see it working.
Frank

I just asked if the controller will work. thats PWM.
the fan is pwm fan.
So i guess this controller will work.

 

[KlausST]

Hi,

oh it works...

The BLDC controller inside the PC fans commutate in a way that the RPM is dependent of applied voltage.

Some PC board work with a very low PWM frequency of some 10 Hz and it still works...

But i take no guarantee that it works with your fan and this controller. Maybe they must fit to each other....

Take a try.

Hope this helps
Klaus

 

[FvM]

I have designed PWM control of BLDC fans for a number of instruments. I turned out that the fans usually have an input capacitor of at least several µF. So it's no good idea to apply a high frequent switched voltage to it as you do with a brushed DC motor. We solved the problem by using an external storage inductor, switching at relative low frequency with slow edges should work too.

 

[xReM1x]

I have designed PWM control of BLDC fans for a number of instruments. I turned out that the fans usually have an input capacitor of at least several µF. So it's no good idea to apply a high frequent switched voltage to it as you do with a brushed DC motor. We solved the problem by using an external storage inductor, switching at relative low frequency with slow edges should work too.

My fan is PFC1212DE. it pwm freq is 25kHz
Will this work ? **broken link removed**

 

[FvM]

I think, the converter should use an inductor series connected with the fan.

 

[xReM1x]

I think, the converter should use an inductor series connected with the fan.

What does it mean inductor series?
and why?
I never saw a pwm controller with inductor..

 

[chuckey]

So with the inductor and the internal capacitor, the "DC" ramps up slowly, the internal chip starts working at some voltage, the fan starts to rotate, the "DC" goes, the fan windmills down in speed. So it is "PWM" controlled its just not PWM as I understand it. Its just on/off DC with a long time constant.
The only way to truly control the speed of a BLDC motor (which is exactly analogous to a three phase AC motor), is to change the commutation speed and supplying the output stage so it is able to deliver sufficient power to actually move the rotor sufficiently from coil to coil at the commutation speed and at the low speed end for the rotor to have sufficient mass so it does not cog from coil to coil in a series of steps ( automatically done with sine wave drive).
Frank

 

[weblinks]

I think, the converter should use an inductor series connected with the fan.

 

[xReM1x]

I think, the converter should use an inductor series connected with the fan.

thats not what someone just said.

 

[FvM]

The inductor suggestion is based on assumptions. It's your job to check if they apply to the present problem.

1. The "PWM controller" as shown in post #6 outputs a squre wave by switching the output between positive and negative supply. It works as a buck converter in combination with the motor's armature inductance. The on/off switching method can be also used to control resistive loads, e.g. filament lamps or LEDs with current limiting series resistor.

2. Some BLDC motors may work with a pulsating voltage, others won't. It depends on the characteristic of the built-in electronics. I already mentioned that many BLDC driven fans have an input filter capacitor. It would generate large peak curents and losses when connected to an on/off switching PWM controller. At worst case there may be just smoke, either from the switch transistors or the filter capacitor. A series inductor is a possible means to make both devices work together.

 

[weblinks]

Hi,friend PWM computer fans. ", I do not understand this. Most BLDC motors have a chip inside them and sensors to control when the current is switched into which coil. When the fan is actuated, the oscillator starts up to "catch" the rotor it then speeds up to accelerate the motor to its operating speed.