PWM issues when powering 4X 4pin 12v fan

Thread Starter

Nimster

Joined Nov 3, 2022
12
Hello all:

I've bought a PWM generator like this one:


s-l1600.jpg s-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!
 

LowQCab

Joined Nov 6, 2012
2,665
You (we) need to know what the functions of the Fan Pins are.

Your Drawing, while it's better than nothing, does not accurately identify the Fan Pins or Wires,
or the PWM-Signal-Generator-Terminals and their functions.

Normally, a 4-Pin Fan will have 2-Power-Pins, a PWM Speed-Control-Pin, and a Tachometer-Out-Pin.

You are showing 2-Ground-Pins on the Fans, this is probably incorrect,
one of them is most likely a "Tach-Out" Pin.

What is the Manufacturer name and Model-Number of the Fans ?
Do You have a Spec-Sheet for them ?

The same thing applies for the PWM-Signal-Generator,
You (we) need a Spec-Sheet for it.
It's unlikely that the "negative" PWM-Out should go to Ground.
Having Positive, and a Negative, ( inverse ) Outputs is probably for convenience in
adapting to Circuits which require one Polarity, or the other.

Most small Fans need a PWM-Switched-Ground to slow them down, not a PWM-Switched-Hot.

The Tach-Out-Terminal or Wire on the Fans should not be connected to anything.

The PWM-Input on the Fans should probably be connected to
the (-) Negative Output of the PWM-Signal-Generator.

But at this point, I'm just guessing.
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Thread Starter

Nimster

Joined Nov 3, 2022
12
Youre right, this is the schematic:

Schematic.jpg

The fan has 4 wires, I'm ignoring the Tac one because I don't need it. This is how I have it connected right now and does not work, fan spins at full speed neither connecting the PWM - to Fan PWM works (At 0% spin fully and after 6% stops).

The controller is this one:

https://www.ebay.com/itm/325342726352?chn=ps&mkevt=1&mkcid=28&var=514271547911

And the data sheet for the fans is this:

https://pdf1.alldatasheet.com/datasheet-pdf/view/943835/DELTA/AFC1212D-SP19.html

I've tried all the possible combinations so far (at least those that make any sense but it seems that for sure I'm missing something)

Thank you!
 

LowQCab

Joined Nov 6, 2012
2,665
The PWM-Controller that You have purchased is for controlling a Motor directly
by controlling ALL Power going to the Motor.

It is NOT designed to be a PWM-Signal-Generator that is designed to work with
Motors that have their own built-in Speed-Control-Circuitry, ( which is what your Fans have ),
so it may, or may not, work with your Fans.
There's a very good chance that it won't work.

Never buy cheap Chinese-Junk that does not provide full specifications, ( usually in a PDF-File ),
unless You have a good idea of what your buying, and,
You are willing to throw it away if it won't work for your needs.

==================================================================

Disconnect the PWM Input to the Fans,
the Fans should run at Maximum-Speed,
if they don't, then the Fans have been damaged by mis-Wiring,
Replace the Fans.

If the Fans will run at Maximum-Speed with the PWM Wire Disconnected,
this is a good indicator.

With the Fans running, touch the PWM-Wire to Ground,
the Fans should either stop, or run very slowly,
this is a good indicator.

=================================================================

If You know how to build a simple Op-Amp-Circuit,
just say so, and I will provide You with a Schematic and parts-list.
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Thread Starter

Nimster

Joined Nov 3, 2022
12
Well it seems that I screwed up buying this. I thought that was going to work for me since in advertises that can work with fans, and I needed something that could be wireless controlled. Well I'm goo with soldering and building stuff so should be no problem to build and OP-Amp circuit. Done a lot of those in my college times. Can you provide the schematic and parts? Will this help to fix the problem?
 

LowQCab

Joined Nov 6, 2012
2,665
Here are 2 different Versions ............
One has a Temperature Sensor if that is useful to You.

They both operate the exact same way, even though they may look different.

If You are sure that your Power-Supply is stable, and will never exceed ~24-Volts,
then You can leave-out the Voltage-Regulators.

In both Circuits,
the OP-Amp-Output can drive the PWM-Pin/Wire from the Fans directly,
with no other parts.

The Frequency of the second Circuit needs to be multiplied by ~10 to make your Fans happy.
The Fans want an approximate ~20khz PWM-Frequency.
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Automatic PWM Fan Control 1 FLAT .png.
Alternative Dimming Circuit Flat .png
 

Thread Starter

Nimster

Joined Nov 3, 2022
12
Hi, to be honest I don't quite understand, is this circuits suppose to be used alone to control the fans or to be used with my "Motor Governor"? I'm asking this because I really need it to be used cause of the wireless thing.
 

LowQCab

Joined Nov 6, 2012
2,665
Sorry, I forgot that You mentioned that You want Remote-Control.
Personally, I'm not at all familiar with what's available,
as I look at "Phone-Remote-Control" as just a "Gee-Whiz" gimmick for lazy people.

It's like controlling your home Thermostat through your Phone ......... why ???

There are certainly devices available that Switch things on and off with a Relay, by way of your Phone,
but as for Remote-PWM-Control, I'm clueless.
I'm also clueless as to what valuable purpose it would serve,
and I'd love to see a real problem solved with it,
it just hasn't happened yet.
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LowQCab

Joined Nov 6, 2012
2,665
It would appear, according to the text, that the PWM-Output has to have a more substantial Load
placed on it before it will generate a PWM-Signal.

This may mean that all You need is a Resistor to provide a Load,
but don't ask me what value of Resistor, I have no idea.
As a guess, I would first try a ~1000-Ohm Resistor, then see if You have
a PWM-Signal on the Negative-Terminal.
It needs to be the Negative-Terminal because that's what your Fans require, a "Switched-Ground".
You can probably safely go all the way down to maybe ~100-Ohms, if 1K doesn't work.
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Thread Starter

Nimster

Joined Nov 3, 2022
12
Basically those are fans of a sever I'm building and I need to control them remotely since the house where the server is is not near me.

So you're saying to put a load between the out - (pwm -) and the general gnd (vin -) right? Just to check if I have a Pwm wave. By the way looking at the fan datasheet it seems it may be a switch to vcc right? Since it seems a pull up resistor.

Screenshot_2022-11-04-00-09-25-56_40deb401b9ffe8e1df2f1cc5ba480b12.jpg
 

LowQCab

Joined Nov 6, 2012
2,665
The Resistor would go between the 2 PWM-Terminals only.
The resistor "may" act as a "Pull-Up" Resistor as well as a more substantial Load.

Fans on a Server are not something that You would want to control Manually,
let alone miles from the location.
Server-Fans should always be fully Automatic.

The first Circuit that I provided will control the Fans Automatically, and with high accuracy,
but the Temperature Range that it was originally set up for may not be appropriate for your needs.
Fortunately it's very easy to tweak the Temperature-Setpoint, and the Temperature-Range.
Let me know if You might want to go that route, and I will help with the
Resistor-Calculations to achieve the exact Temperature-Set-Point and Range that You need.
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LowQCab

Joined Nov 6, 2012
2,665
I should have said .....
Server-Fans should never be turned-off, or even slowed-down, period.
And they should be replaced once a Year, even if they're working perfectly.
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Thread Starter

Nimster

Joined Nov 3, 2022
12
It's a small server not the ones where you can host websites. It's small project and since it makes very cold, I can turn the fans on/off as well as the AC in the winter.

Regarding the resistor I was asking where should I put it because you said the PWM OUT - was not GND and always though I needed to connect one terminal to GND to make a load.
 

Thread Starter

Nimster

Joined Nov 3, 2022
12
Last edited:

Thread Starter

Nimster

Joined Nov 3, 2022
12
This is the wave I currently have. When decreasing duty cycle it actually is increasing. It may be related with the Pwm being active low.

IMG_20221104_143748.jpg
 

BobTPH

Joined Jun 5, 2013
6,093
Yes, you need to invert the output, as others gave suggested. Do you know how to use a transistor as an inverter?
 
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