When one goes to buy a new axial flow cooling fan these days there's always the flow curves and the maximum acoustic noise numbers to go by, but this doesn't tell anyone what sort of performance can be had with reduced drive voltage. At very low output, the flyback pulse in a two phase brushless stator can be the major source of acoustic noise (never mind electrical). Older max efficiency / low chip dissipation driver ICs have only protection level control over the flyback pulse, while some better and maybe newer chips have the unipolar driver transistor bases available so that a capacitor to the collectors can be added, effectively using the output transistors as a damper (as I understand it). These yield very low acoustic motor noise. The Problem is no fan manufacturer, that I know of, even bothers to mention what ICs are used in their product, let alone showing the applied circuit, and therefore most people that haven't tried them all really doesn't know what to expect from the stock product.
Anyone out there with some greater insight to this?
Anyone out there with some greater insight to this?
and what to expect? You buy cooling fans fit for a purpose. Acoustic noise, long life, cfm performance all can be prioritized. The fan blade design , bearings used, power, rpms, and expected lifetime. Users operating outside the designed input drive parameters, yer pretty much on your own, right? The electrical parts used is probably a 3rd order effect under blade design, rpms, ducts, baffles, or pressure loads...IDK perhaps yer OCD has taken you on super duper deep dive, time to come up for fresh air.
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Thanks infinia. It looks like you're all I got. I have plenty of problems, but no OCD. Most DC fans now are mfr specified to operate in a range of voltages, but that's as far as it goes. I'm not making it up that toward the bottom of the allowable drive range the stator makes the most noise on a lot of available product. It's seems silly as often at half rated voltage (bottom of specified range) the blade noise is impossible to hear unless your ear is almost on it but you can hear the motor from across the room.
Quiet fan motors are getting much more popular and widely available, mainly from the PC builder crowd. The motor driver manufacturers are focusing more on radiated acoustic and electrical noise now, but there's no way that I know of to tell which fans are using the better drivers, and in configurations optimized for noise, unless there is a developing user-generated database (like exist for so many other audio components) that I'm unaware of.
Quiet fan motors are getting much more popular and widely available, mainly from the PC builder crowd. The motor driver manufacturers are focusing more on radiated acoustic and electrical noise now, but there's no way that I know of to tell which fans are using the better drivers, and in configurations optimized for noise, unless there is a developing user-generated database (like exist for so many other audio components) that I'm unaware of.
Why not buy a couple of fans from your top two suppliers, and then experiment with building your own speed control circuitry? You could try all-analog, pure DC voltage control. You could try Pulse Width Modulation using rectangular pulses. You could try PWM using trapezoidal pulses (which reduce harmonics). You could try DC + inject-a-pulse kinds of naughty schemes to guarantee startup while running at low speeds from very low DC voltages.
A dual opamp, an 8 pin microncontroller IC, a handful of passives, a couple of medium power transistors, and a big boatload of innovative ideas and creative approaches. Why not give it a try?
A dual opamp, an 8 pin microncontroller IC, a handful of passives, a couple of medium power transistors, and a big boatload of innovative ideas and creative approaches. Why not give it a try?
It's hard to justify such a project when you know darn well your target design is being mass produced by major suppliers for 10 to 20 bucks a piece single quantity. It's just a matter of finding it. I know NMB makes a nice quiet motor in their 4710KL series, but this is an old product and I know serious advances in fan motor controllers have occurred since its release. Possibly the most effective time expenditure would be to contact the top fan manufacturers and suggest they release more comprehensive, modern datasheets to include the radiated noise at minimum drive or at a maximum do that and also divulge the driver IC used and show the applied circuit. I know the latter is probably a dream but the fact is many designers would quickly and well understand the relative quality of the product if this info were available. It could potentially improve sales for almost no cost.
The only good argument for building my own is, these days, there's probably no one considering linear sinusoidal drive, which would probably be the best far as any kind of noise, if you're willing to lose a few more watts. I'd really rather just buy something close.
The only good argument for building my own is, these days, there's probably no one considering linear sinusoidal drive, which would probably be the best far as any kind of noise, if you're willing to lose a few more watts. I'd really rather just buy something close.
It's easy to pick the quiet PC fans, each OEM has some line of quiet fans, theyre the ones at low RPMs and lousy CFMs. To get any decent cooling you then must go upsize.
~120 mm.. now days, AFAIK 80mm and 92 mm case fans are dead ends unless running duals or triples. What are the instrument, PS vendors , electronic load OEMs using, surely not PC fans? I bet they use better ducting schemes.
see here for reviews SPCR • View forum - Fans and Control
~120 mm.. now days, AFAIK 80mm and 92 mm case fans are dead ends unless running duals or triples. What are the instrument, PS vendors , electronic load OEMs using, surely not PC fans? I bet they use better ducting schemes.
see here for reviews SPCR • View forum - Fans and Control
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