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PWM issues when powering 4X 4pin 12v fan

Nim

Nov 3, 2022
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Nov 3, 2022
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Hello all:

I've bought a PWM generator like this one:

s-l1600.jpgs-l1601.jpg
And I want to connect it to 4x 12V Fans with PWM connector but I'm having some issues. Basically I'm connecting things this way:

Schematic.jpg

But I'm always getting the fans to rotate at full speed with no control at all. Also tried to disconnect the GND that connects the PSU to the FAN HUB, and I was able to control the fan but they stop and start, the speed is not constant. I also notice that where I should have 12V constant I get oscillations. If I measure between IN+ and IN - I get 12V but if I measure FAN1 between VCC and GND I get the same oscillations that I get measuring between PWM and GND. Am I having some ground issues?


Thank you all for the help!
 

kellys_eye

Jun 25, 2010
5,107
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Jun 25, 2010
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5,107
Are you changing the pulse WIDTH to regulate the speed or pulse FREQUENCY? It should be 'width' (i.e. the % setting). The frequency setting may also be applicable - have you got the spec sheets for the fans?
 

Nim

Nov 3, 2022
6
Joined
Nov 3, 2022
Messages
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Hello,

I've left the frequency at 25Khz I'm only changing the duty cycle and if I have it connected like the schematic it does not work. If I disconnect the gnd that goes from the PSU to Fan Hub it works but the fan keeps speeding and stoping cause I have oscillating tension where it should be 12v constant.

The data sheets are these:
 

kellys_eye

Jun 25, 2010
5,107
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5,107
Is there an electrical path from the power (ground) pin to the signal output 'ground'?

Got a link to the PWM device you're using?
 

Nim

Nov 3, 2022
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Nov 3, 2022
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Hello, no there is not. The In- is not connected to the Out - on the Pwm Generator. Already tried to connect only the out- and out+ to fan Pwm but still no go.

This is the link:

 

kellys_eye

Jun 25, 2010
5,107
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Your schematic shows you using a BLUE wire for the PWM signal - if this is what you're doing then it's wrong as the PWM is supposed to attach to the YELLOW wire. The blue wire is a signal OUT of the fans for monitoring purposes.
 

Nim

Nov 3, 2022
6
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Nov 3, 2022
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In my case its the blue wire. The PWM is connected correctly. I manage to fix this using this circuit:

https://maker.pro/forums/threads/pw...fan-without-a-motherboard.289391/post-1773996

This way it works but with a little problem, when I put 100% duty the fan stops and at 0% it spins at max speed. It seems that I have a low active pulse and need a high active pulse. Already tried to use this:


But without luck. I've mounted this circuit using the inverted pwm as input but all I have now is 0% stopped, 1% or more full speed.
 

kellys_eye

Jun 25, 2010
5,107
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Jun 25, 2010
Messages
5,107
I manage to fix this using this circuit:
Looks as if the PWM generator has an open-collector output hence the use of a pull-up resistor. The sellers information on the PWM device isn't specific on it's actual output hence my query about checking whether the -ve supply rail connects direct to the -ve PWM output. That it isn't connected indicates the open-collector situation but you should be able to get the right 'polarity' using the +ve output and the pull-up resistor.
 

Nim

Nov 3, 2022
6
Joined
Nov 3, 2022
Messages
6
Looks as if the PWM generator has an open-collector output hence the use of a pull-up resistor. The sellers information on the PWM device isn't specific on it's actual output hence my query about checking whether the -ve supply rail connects direct to the -ve PWM output. That it isn't connected indicates the open-collector situation but you should be able to get the right 'polarity' using the +ve output and the pull-up resistor.

The +ve and +ve output are connected internally. I've checked that using a multimeter. I've tried connecting the +ve output to a Pull up resistor but all I get is full speed on fan. Can you help me? Using the Pull up on ve- output I get the problem that at 100% fan stops and 0% spins fully. The ve- and ve- output are not internally connected.
 
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