PWM to control brushless 12VDC fan speed
PWM to control brushless 12VDC fan speed
(OP)
Looking for some help to control the speed of a brushless 12VDC (120mA) fan from a 0-5V 500Hz PWM signal.
Here is the fan.
http://ww w.newark.c om/sunon/k de1204pkvx -ms-af-gn/ axial-fan/ dp/89K1822
I tried simply sending the PWM through a 220ohm resistor to the base of a transistor and 12vdc through the red wire, black wire to the collector and emitter to ground. It worked fine when at 100% duty cycle but anything lower and the fan just stalls and buzzes.
Here is the fan.
http://ww
I tried simply sending the PWM through a 220ohm resistor to the base of a transistor and 12vdc through the red wire, black wire to the collector and emitter to ground. It worked fine when at 100% duty cycle but anything lower and the fan just stalls and buzzes.





RE: PWM to control brushless 12VDC fan speed
RE: PWM to control brushless 12VDC fan speed
RE: PWM to control brushless 12VDC fan speed
RE: PWM to control brushless 12VDC fan speed
I was hoping one of you smart guys might have a solution.
RE: PWM to control brushless 12VDC fan speed
RE: PWM to control brushless 12VDC fan speed
Nonetheless, you might see some speed difference between 4.5 VDC and 12 VDC.
TTFN
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RE: PWM to control brushless 12VDC fan speed
RE: PWM to control brushless 12VDC fan speed
RE: PWM to control brushless 12VDC fan speed
You cannot PWM any DC brushless motor, newer or older. It's already doing pulsing internally; external pulsing just screws up the control circuitry.
TTFN
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RE: PWM to control brushless 12VDC fan speed
There are plenty of fans and fan controllers sold for PCs. But most would use more than 1.4 watts.
But obviously I don't know what you're up to...
RE: PWM to control brushless 12VDC fan speed
No, you need a naked brushless motor if you want to do your own pulsing, which means a minimum of 3 windings, or phases. Anything that's described as a "DC" brushless motor has an internal controller.
TTFN
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RE: PWM to control brushless 12VDC fan speed
I assume during the dead-time of your PWM the fan voltage drops below 4.5V. This causes the integrated brushless DC motor controller to turn off. During the on-time, the motor controller powers up again, but not long enough to get the fan spinning. You could add a capacitor in parallel with the fan to keep the fan voltage above 4.5V during the dead-time. The capacitor would charge almost instantly through the transistor, and would slowly discharge through the fan. For an input voltage of 12V and a minimum output of 4.5 volts, the RC time constant of the fan/capacitor should roughly equal the PWM period.
The apparent fan resistance of the fan motor / BLDC motor controller is 100 ohms (.12A @ 12V). For a 500 hz PWM rate, the capacitor should be approximately 20uF. This value could be reduced by increasing the PWM frequency.
RE: PWM to control brushless 12VDC fan speed
I did try a cap across the fan but I didn't use one large enough (didn't run the math..just threw a 1uF cap out of my bin on it). Might find a 20uF and try that again one more time before I switch directions as below.
Now I'm planning on switching the fan to be fed from an LM317. LM317 output will be digitally set to have 3 different output voltages. 2 digital outs from my micro feeding the base of a transistor to drop in a parallel resistor to vary the LM317 output. Like figure 11 of this datasheet http://www.st.com/stonline/books/pdf/docs/2154.pdf
I really only wanted/need 3 fan speeds anyways and not completely variable.
Something like..
(both digitals off=12vdc from LM317) (dig1=high, dig2=low =8vdc from LM317) (dig1=high, dig2=high =6vdc from LM317)
That should get the job done.. It's a side project for home anyways.
RE: PWM to control brushless 12VDC fan speed
TTFN
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RE: PWM to control brushless 12VDC fan speed
RE: PWM to control brushless 12VDC fan speed
I have a large Quadraphonic receiver/amp (remember those?)in my machine shop that someone gave me,and the internal fan shot craps.So, I have a 12V pancake fan sitting on top of the amp, powered by a 12V 1.0A "wall wart" transformer, which is in turn plugged into a variac. By varying AC to the transformer, I can reduce the fan speed (and noise), but still keep the amp from overheating.
not sure where this places my 'carbon footprint'.