Most Sunon fans are are not compatible with PWM control that cycles the power supply due to the design of their controller electronics. They usually work fine with uninterrupted (smooth) DC though. Typical PWM fan control is achieved by supplying the fan with constant power supply voltage (such as 24V) and a separate PWM control signal. The way 3D printer controllers try to do this is a “brute force” simplified approach. This simplified method also can cause the fans to make unusual noises and can cause some fans to fail prematurely. Fan manufacturers sometimes declare if their fan controllers are compatible with PWM cycling of the power supply.
You can still use these fans with PWM modulation of the power supply but they would require a “PWM to DC” converter of sorts, for example something like this: Silent Fan Driver.
The PWM contolled DC/DC converter an interesting suggestion but I’d caution against using it in this situation. Sunon (and many other similar) fans not designed for PWM operation contain electronics that are designed to run the fan at the specified speed when power is applied at the specified voltage range.
The electronics will strive to keep the fan running at the specified speed and if the input voltage drops to the point where it cannot maintain the speed it will treat the situation as if the motor is stalled and perform an automatic shutdown with the goal of protecting the motor from burning out. To reset the automatic shutdown all power must be turned off (maybe for a specified amount of time) and then full power applied for the fan to start up again - I’m not 100% sure for the motors you’re using (@button does not give the part number of the fans he’s using).
Unfortunately, the solution is to replace the Sunon fans with ones that can accept PWM power control or use fans with a separate PWM control line (Sunon provides this option but, from what I can see they do not have PWM controlled fans in the typical 3D printer sizes ie 40x40m and smaller).
You are right @mykepredko, basically no 2 wire brushless fan is particularly happy about being driven by PWM but surprisingly most work somehow (however some do not at all).
Some only work at PWM frequencies of 100 Hz (Klipper’s default), some are even happy with 500 Hz and above. Note that true PWM fans operate at >20 kHz.
No idea. The usable range should also depend on the clock and capabilities of the MCU and if they have high resolution timer or not etc.
Also I do not know if the Klipper code is imposing any limits.
I’m not 100% sure this is correct. I believe that there are small BLDC chip sets/electrical designs that do support modest PWMs (as you noted less than 500Hz).
What I am sure of is that Sunon fans don’t and are designed to be quite intolerant of anything other than specified power.
Most two or three wire (non PWM controlled) Sunons I’ve worked with in my hobbies (maybe handful of different series) are perfectly happy and are in-fact specified in their data sheets to work over a fairly wide voltage range below their design voltage. Their flow rate vs. voltage is naturally very nonlinear, so one would need to define it, even if it’s for basic understanding of their characteristics.
I had great success with simple low-pass-filter (LPF) based “PWM to DC” converters with those fans. In my Creality I am using a Sunon that does not even start when PWM is applied to it, because as @mykepredko pointed out their anti-stall circuit kicks in and with its time delays effectively makes the fan inoperative. You can make it work, by the way, if you slow down the PWM frequency sufficiently to drop below their circuit response time - but who wants a fan that starts and stops once every 2 seconds or so. Instead, I characterized my specific fan current draw at the range of supply voltages that Sunon publishes for it, in as-installed configuration, to make sure that the load was representative. With the current vs. voltage curve I defined a very simple RC LPF (diode isolated) that provided the most linear range of speed control using increased 1kHz input PWM frequency (allowing use of smaller components). This circuit feeds the fan a reasonably low ripple DC that is roughly proportional to the PWM duty cycle. It works extremely well. A better design with lower voltage drop, but slightly more involved to implement, would use an LC low pass filter. I have parts for one but have not had the time to design the PCB and to implement it. The components in this case also have to be somewhat matched to the fan electrical characteristics…
In case of the MF40101VX-1000U-A99 fan , the data sheet clearly states to NOT drive it with PWM, similar to the fan I am using with the LPF on my Creality case:
7. DO NOT use power or ground PWM to control the fan speed. If the fan speed needs to be adjusted, please contact SUNON to customize the product design for your application.
