High-performance fans—that is, those that are high in RPM and have high air movement—aren't known for their super-quiet modes of operation. Rather, they can be extremely noisy, especially for those very-small and very-powerful fans. I've seen some fans as loud as 85dB and, as you may know, 85dB is near the sound level at which ear damage becomes possible.
Sure, high-performance fans will never be silent operators, considering their purpose in life, which is to move air at high rates. However, noise issues can be mitigated by improving the bearing design, and that's what CUI has accomplished with their CFM-V line of DC axial fans. According to CUI, these fans have noise levels from 10.7 dB to 48 dB and are good options for telecommunication equipment, medical devices, and industrial systems.
As CUI describes in their omniCOOL technical paper, this new bearing system uses a magnetic structure, in conjunction with an enhanced sleeve bearing, that "effectively makes the rotor work like a spinning top—but one that never falls over and can operate at any angle."
Seems like a good idea! I wonder why this approach wasn't thought of, or adopted, before now.
Figure 1. Cross section of a fan motor with the omniCOOL system. Diagram taken from this technical paper.
The life expectancy of CUI's omniCOOL fans is also impressive; the figure below shows the useful life data.
Note: The table would be easier to understand if the unit of "hours" were included/associated with the numbers—I had to refer back to the graph to verify what I was looking at. Missing units in such tables is a pet peeve of mine.
Figure 2. Life expectancy comparison, taken from this technical paper.
Besides reading the technical paper on CUI's omniCOOL System, I also reviewed the CFM-120V datasheet. And according to the datasheet, the life expectancy of the fans is 70,000 hours at 40°C and 65% relative humidity; this closely matches, as it should, the information in the technical paper. A big difference that I noticed, however, was the addition of the relative humidity spec in the datasheet (i.e., it’s missing from the technical paper). To me, this isn't a big deal, but it does reinforce the notion of always check the datasheet.
There is one item in the datasheet that is moderately alarming, and that is item #16 on page 10 (“Safety Considerations”): "The life expectancy of these fans has not been evaluated for use in combination with any end application. Therefore, the life expectancy that relate to these fans are only for reference." Hmmm...okay, I guess I won't bet my life (pun intended!) on these life expectancy curves. But still, the temperature vs. hours of operation curve is remarkable, specifically at temperatures greater than 70°C!
Auto Restart Protection, Rotation Detector, and Tachometer
I give CUI credit for providing so much useful technical information in their datasheet, including the electrical specifications, the multiple performance curves, the mechanical drawings, and the application notes (page 9), which include information on
- auto restart protection
- the rotation detector signal
- the tachometer signal
I find the written descriptions together with the diagrams to be very helpful. In the interest of full disclosure, I haven't used fans in any major designs for about 8 years. So I haven't read too many fan datasheets recently, and maybe CUI's datasheets with their abundance of information are the norm these days. However, years ago when I was pouring over multiple fan datasheets, I found that most were rather stingy with the technical content, which was very frustrating.
Figure 3. Tachometer signal application information, taken from the datasheet.
Multiple Speed Options for Different Cooling Needs
One of the advertised features of these fans is "multiple speed options for different cooling needs." After first reading this feature highlight, I thought that either the fan has a speed-control wire or the datasheet provides speed-performance curves based on the input voltage range. But I discovered, after digging a bit deeper, that I was wrong on both counts.
Item #7, again from the “Safety Considerations” section, states, "If the fan speed needs to be adjusted, please contact CUI to customize the product design for your application." Oh, now I see... so I must contact CUI for my “multiple speed options” needs. Bummer.
Have you had a chance to use this new omniCOOL technology in your designs? If so, leave a comment and tell us about your experiences.
Featured image from CUI.