Electronics > Beginners
Trying to build a PWM fan controller
eamoex:
Hello Everyone,
first, please know that I'm a total newb, and so I use language which is almost certainly wrong. I do things which are almost certainly stupid. But I'm not all that young anymore, have no one around to teach me and rely on information and hardware gleaned here and there. So please don't bash me...
So. I would like to build a 556-based PWM fan controller. I found this schematic:
on this [url=http://www.overclockers.com]www.overclockers.com page[/url].
I've started breadboarding it and have made some progress, i.e. the PWM output lead does its job (or so it seems to me anyways) but I don't get how the PWM signal is "interpreted" by the fan. The 556-based circuit does change the signal's duty cycle, but fan speed follows some indetermined curve, going slow in the middle and fast at the ends. It also doesn't seem to span the full spread of available speeds, i.e. when it's slow, I think it could actually be much slower.
I've triple checked the circuit and think all is right according to schematics.
Here's a video of my being ignorant with my donated 1-channel oscilloscope: http://www.emyamstein.ch/media/forums/IMG_0410.MOV
The fan is this: https://www.amazon.com/Noiseblocker-.../dp/B00839GBC6
Also, I know that you savvy people know better, more elegant ways to achieve PWM control, but doing this is a lot of fun to me, although certainly clunky-looking for the expert.
Can somebody please tell me what's wrong with the circuit? Or me?
jmelson:
Does your fan have a logic-level PWM input, or is it just a plain 2-wire fan? If 3-wire with PWM input, then check the data sheet to find the optimum PWM frequency and duty cycle range.
If a 2-wire fan, then you will have to run the PWM at a low enough frequency for the fan to work right. Many 2-wire fans have a start-up mode that they execute every time power comes on to get the rotor started, and this will likely interfere with PWM speed control.
Jon
eamoex:
Thanks for your reply.
It is a 4-wire, tach + PWM input fan. The datasheet unfortunately doesn't say anything about frequency or duty cycle. It boasts about propeller and case material, longevity, low acoustic dB... just about anything but that information.
I've reached out to the company to get the data. I'll see what I get...
spec:
Hi eamoex
Here is a datasheet which shows the fan speed range:
https://www.blacknoise.com/datas/downloads/datasheets/TData_BSP8025_122012_de_en.pdf
It seems odd that your fan has a four-pin connector because the Amazon advert states a P1 version (3 pin Black=0V, red=12V, yellow=taco op). The four pin version is PP.
The schematic for the PWM has no values, which means we can not analyze it.
Also we would need a complete schematic of your circuit from the power source to the PWM to the fan. Presumably you have a 5V and 12V power source.
grumpydoc:
If it is standard computer 4-wire +tacho there is a specification to which it should adhere.
https://folk.uio.no/kyrrens/diverse/viftekontroller/developer-specs-REV1_2_Public.pdf
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