What is the viable option for high CFM low noise 120mm fans nowadays?

[Ajay57]

After all the science lesson on here, it still boils down to trying things out practical wise!!

1, http://martinsliquidlab.org/2013/05/07/fan-testing-round-12/

As far as that goes this has been my guide and never let me down so far!

AJ.

 

[NiHaoMike]

but the pwm signal from the motherboard doesnt go into the windings it doesnt power anything, its just a 5v signal for the board inside to figure how fast for the motor should be spinning.

Almost correct. It's a 3.3V signal.

The PWM that actually drives the motor is generated by the control circuit in the inverter.

 

[wagex]

im fairly certain its a 5v signal, i have made a couple pwm controllers for pwm fans...

 

[Blaylock]

This thread has gone from discussing high CFM quiet 120mm fans to...well, something different. Can we please get back on track? (Maybe start a new thread on the debate of what a sine wave is and what a PWM signal is - just a suggestion)

 

[Bobnova]

It's both.
Spec is/was a 5v pullup inside the fan, recommended spec is a 3.3v pullup inside the fan w/5v tolerance.
Hence, you can use either one.
Officially speaking you don't need to source any voltage with a fan controller, just sink it. Convincing a 555 timer to sink-only is a good trick though, and the fans certainly don't care if something else is sourcing the pullup (they might care if you sourced 12v or something of course).

Mike, am I correct in assuming that the scope shot is of a 3phase fan? I'm making that assumption based on their being a neutral.
Neither trace looks especially sine waveish to me, but the bottom one is less square for whatever that is worth. The IC you linked specifically says it doesn't care about input PWM frequency.


Blaylock, Blackjackel, whoever wants an answer to this thread's original question: What do you consider "high CFM", and what do you consider to be "quiet"?
I realize it's a cheeky question at best, but it's also rather crucial.
What I consider to be "quiet" and what Mike considers to be "quiet" are two rather different things, for instance.
Similarly what Mike I consider to be "high CFM" (I think we agree on that one, heh. HIGH LIKE HIGH) and what you consider to be "high CFM" are probably quite different as well.

 

[wagex]

theres some ap 14's on ebay pretty cheap like $15 iirc
like bob said quiet is dependent on the person like for me 120mm fans is 1200rpm 80mm fans 2krpm both are pushing it
some would argue 3krpm or 5k if they are deaf lol i got some 120x38mm yate loon lows which push some good air and are quiet turned down to 7v

 

[NiHaoMike]

Mike, am I correct in assuming that the scope shot is of a 3phase fan? I'm making that assumption based on their being a neutral.
Neither trace looks especially sine waveish to me, but the bottom one is less square for whatever that is worth. The IC you linked specifically says it doesn't care about input PWM frequency.

It is in fact a 3 phase fan, as is typical of higher power fan motors. The smaller ones are typically 2 phase (split phase, sometimes misleadingly called single phase) as they are more compact. Main advantage of 3 phase is that only 6 power MOSFETs (as opposed to 8 for 2 phase) are needed.

If you mentally visualize the phase to neutral voltage (what the motor windings see), you'll find that it is in fact pretty close to a sine wave. Add in the low pass filtering of the motor and the current waveform (what the motor actually cares about) would be even closer to a sine wave.

The datasheet says that the chip will accept anywhere from 20Hz to 100kHz PWM. Definitely a very wide range, but go outside and at some point, it won't operate correctly.