Why do you need a fan?
If only the hotend needed the air movement,
a single carriage fan would suffice, yet I get better results with double carriage fan.
So first and foremost the print itself needs the fan.
Buying fans for the carriage
Choosing the right fan is not easy. The ideal fan must be able to be driven directly from a PWM output of the RAMPS.
Many fans are not capable of be driven from a PWM output,
so it's mostly a hit and miss when buying small fans.
Why is a MagLev fan cool?
Well, the magnetic levitation itself is cool:) Also it is more efficient per watt (has more air blow power) than a ball bearing or bushing fan.
In my case the ball bearing fan can blow a lit match from 14 cm away, while the MagLev fan can blow it out from 41 cm(!) away.
So roughly 3 times more blowing power.
What to do if the fan is not able to be driven from PWM output?
I discovered my Maglev fans are not able to be driven from PWM output, they only work
with M104 S255, and not any value from 0-254.
Issuing a command less than S255 makes a strange pitch noise instead of turning the fan.
So I started experimenting, and I figured that I only need to add a small capacitor (any electrolite type capacitor works) between 4.7 uF and 100 uF.
(YMMV and also warning: some type of fans does not rotate even with this modification)
(note the superbright yellowish green clamp in the background:)
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