PWM isn't working with new 40mm cooling fan

[Paul]

Hey folks,

I upgraded my wimpy 40mm fan to this one (http://www.ebay.com/itm/Dynatron-Top-Motor-DF124028BA-3-DF1204BA-40mm-x-28mm-fan-Ball-Bearing-/370578213372?pt=US_Computer_Case_Fans&hash=item56482ec9fc).  It pushes a ton of air and works great, but unfortunately when I run it at any PWM setting, the motor stalls and doesn't work (even at 95% PWM).  I suspect this effect has to do with the PWM frequency setting in Marlin, and I might need to increase or decrease it.  I've tried to find out how to change this, but can't seem to find out how to change this setting (I've done a little Google searching, but can't find a guide on this).  

Thanks for any guidance!

[copperclad]

Hi
This link might be of some help
https://groups.google.com/forum/#!topic/mendelmax/R4xg1nY1OYs

[Mike Payson]

That fan won't work. three wire fans need a special controller. You need a two wire DC fan.

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[Paul]

Isn't the 3rd pin just a signal wire to communicate fan RPM to a motherboard (or similar electronic device)?  It shouldn't have any bearing on the control of the fan.  Maybe you are thinking of a 4-pin fan?

[Mike Payson]

A 3 pin fan is a brushless motor, that requires a special circuit to drive it. See http://www.ehow.com/how_12121984_control-3-pin-brushless-dc-motor.html for an explanation. A "normal" dc fan has just two wires, and is controller with a normal PWM signal. I have no clue what is up with 4 pin fans, but my guess would be they are also some sort of brushless motors.

On Thu, Jul 4, 2013 at 11:31 PM, Paul <paulne...@gmail.com> wrote:

Isn't the 3rd pin just a signal wire to communicate fan RPM to a motherboard (or similar electronic device)?  It shouldn't have any bearing on the control of the fan.  Maybe you are thinking of a 4-pin fan?

--

[copperclad]

Hi
A lot of the two wire fans are brushless also. They may be labeled 12 volt DC , but if you open them up they are brushless . It is my understanding that the fans manufactured for computer applications tend to be brushless because of the unwanted electrical noise or hash caused by brushes. HTH

[Kamil]

Paul is correct, the 3rd wire sends a simple pulse from a hall effect sensor, or the electronics themselves, in the internal fan electronics as a tach signal back to the MB in PC type applications.

copperclad is correct as well on both points. Brushed motors generate static noise, as the brushes move from one pole to another across the commutator. Also there is dust generated from the brushes themselves as they wear.

4 wire PC fans work similarly to 3 wire fans and get a duty cycle, PWM, signal on the 4th wire to tell the electronics when and for how long to supply current to the drive circuit to vary the RPMs of the fan. This was implemented to reduce the harmonic drone of a steady RPM of a fan. This way the fan is constantly slowing down and speeding up due to the PWM signal. The voltage is kept at a steady 12V, to keep the drive circuitry energized at all times.

Some 2, 3, and 4 wire fans don't respond well to being driven from a pulsed voltage source. This is due to the circuitry inside the fan as was explained in the thread copperclad mentioned. The drive circuit is not energized long enough for the current to actually get passed to the coils to drive the fan motor. These fans typically respond better to a variable voltage source hence why so many PC fan controllers are a simple variable resistor pot. To that effect, even 4 pin PWM fans can be driven off of 2 wires, albeit at full speed, unless they can handle a current less than 12V and still energize the motor coils if one wanted to control the RPMs by varying the voltage.

Mike the type of fan you mentioned is a little more of a special use case and not typically used in PC type fans.

I have a couple of Top Motor fans that I have salvaged off of cheaper PC power supplies. While I have not tried them in a PWM application, as I'm running my MM2 on 24V, they work OK when the RPM is varied by a resistor or a PC type fan controller like I mentioned above.

[Paul]

Thanks for the responses guys.  I've gone through the thread, but it still doesn't address if/how you can change the PWM frequency within Marlin on RAMPS.  That said, this effort might all be in vain if the fan is indeed brushless (with a brushless electronic speed controller built into the fan).  I suspect it might be since you'd think that even a very inductive fan would work at a very high duty cycle PWM.  Instead, the fan starts cogging even at 99% duty cycle.  Maybe I'll open it up and take a look.  If this the case, it means I really would need an external brushless controller (or modify the internal one), as Mike suggests.  It'll probably be easier to just pick up a different fan :P.

[Greg. L]

Or just put a low pass filter on, as described in the thread linked at the top. You'll likely find that locating a DC brushed fan is fairly difficult.

[Byrom Dorsey]

I've got two of the ones that Maker's Toolworks sells: 

http://store.makerstoolworks.com/electronics/fan-40-mm-24-v/

and they work great on my MM2.0.  The spec says 12CFM on that one, which is close to 11.5CFM on your e-bay one.  (I know, you probably can't trust either figure......)  They're a little cheaper than yours, too.

But just pointing out that they do seem to work well.  I'm using OhmEye's flat-looking fan mounts.  I can't say whether that's the best configuration because I was just blindly following someone who's better than I am. 

Byrom

[Byrom Dorsey]

I just realized that yours was 12V and the link is to a 24V fan.  Sorry.