All that will happen is your setting speed will drift over time and temperate as there is no feed back to correct the controls. It will not damage anything. The fans I am familiar will run full speed if there is no PWM connection.
If your fan is a standard PC case fan it is going to be controlled with a 3.3v logic on the control line. The pulse line is going to be an open drain collector so you have to use an INPUT_PULLUP and it is going to be pulled low twice every revolution of the fan. There's a standard that these fans use.
Once I violated all rules, against the "expert seller". "Can't be PWM:ed"...
Take any fan You like, hold the last power cord in Your hand and "dip it" to the fan. What happens? The fan makes a short rush.!!!!! That means You can speed control any fan!
There are fans having built in circuitry.... In that case use a rather low PWM frequency like 25 Hz, or maybe I used 250 Hz.
Thanks everyone -- So it's clear to me now that the schematic above is off base.
Ah right, I misinterpreted the spec, thanks.
My goal here is just to have a 24V PSU and a controller module of some kind with a pot on it that I can use to set the speed of the fan.
So maybe what I want is to just feed 24V right to the fan and have a separate PWM board that sends an adjustable duty cycle square wave at 25kHz. Seems like most are 5V but I'm getting the picture that fans will be OK with 3.3 or 5?
So, am I correct that there are three routes I can go here:
feed the fan 24V directly, and send a ~25kHz 5V PWM signal via an external module
feed 24V to a "fan governor" board like this, connect the +/- of the fan to the board, and the PWM pin of the fan to the "PWM" pin on the board*
feed 24V to a "motor speed control" and the +/- output of the board to the fan, bypassing the PWM pin entirely. AFAIK this means the supply to the fan is just chopped up at some duty cycle. Feels kinda brutal to me but maybe that's normal?
(*I know that's a 12V board... maybe I can find a 24V version... maybe not...)
...I see some references to people controlling fans this way, but pulsing the power via 25 kHz PWM seems to me a kind of rough way to control a fan (especially one that has a PWM pin that I'm ignoring in this scenario)... is this a normal/safe way to do it?
Thanks -- the fan requirements for this application (blowing sand around through tubes) are pretty specific and I don't know if I can get the static pressure I need with a 12V fan. (E.g. that fan I linked can do about 2.5 inH2O at 35 CFM.) Maybe I'll give another look at the 12V fans though and see if I can find one with the oomph...
(I did find at least one 24V governor... ships from China.)
Edit: 12V version of the same fan had the identical specs, so it wasn't an issue.
Ah yeah: "We are currently working to fix an issue affecting the performance of our website. We apologize for any inconvenience and expect to have the problem resolved very soon."
