Bearing matters for low RPM?

thejamppa · Post by **thejamppa** » Mon Aug 03, 2009 1:25 pm

Hi!

I am not genious when it comes electric engineering or electric motors so maybe someone better knowing can explain this:

I had 1150 rpm Scythe Gentle Typhoon and 1200 RPM Scythe Slipstream.

I changed Scythe Slipstream that RPM'ed 960 to 1000 rpm on Chassis fan header as exhaust. After changing fan into Scythe Gentle Typhoon the GT rpm'ed 720 rpm's from same fan header withotu changing anything but the fan.

Both are 3-pin fan with almost identical RPM's. Yet GT rpm's siginificantly lower rpm in Idle. Only difference in fans are Bearings. Slipstream is regular sleeve bearing while GT is dual ball bearing fan.

Fan specs

Model - Name - Starting voltage - Stating RPM
SY1225SL12M | Slip Stream 1200 | ~ 3.5 V | 580 rpm
D1225C12B3AP-13 | GentleTyphoon 1.150 rpm | ~ 4.5 V | 330 rpm

Its also intresting that while Sslipstream has lower starting voltage it has significantly higher starting rpm...

Do bearings really matter this much? Or is there something I have missed? Maybe Sample variance?

b_rubenstein · Post by **b_rubenstein** » Tue Aug 04, 2009 7:09 am

It has nothing to do with the mechanical aspects of the fans (bearings). It due to the differences in the motors. As you noted, the Slipstream has a lower staring voltage, and probably draws more current at 12v. Are you sure that the fan header isn't under BIOS control and is delivering a full 12v?

(BTW, I've been using the same 1150 RPM GT for several months and think that it's an excellent fan.)

thejamppa · Post by **thejamppa** » Tue Aug 04, 2009 7:25 am

No its bios controlled but 1200 rpm model Slipstream never has been able to run lower than 960 rpm's there. However there's significant difference in ampers

Slipstream 1200 rpm 12v/0,26A
Gentle TYphoon 1150 rpm 12v/0,034A

spookmineer · Post by **spookmineer** » Tue Aug 04, 2009 4:28 pm

Just a thought...

Slipstream amperage suggests its motor is much stronger than the Gentle Typhoon, therefor it's easier for the SS to overcome any backpressure from obstacles in the airflow, and hold its target RPM better than the GT.

thejamppa · Post by **thejamppa** » Wed Aug 05, 2009 12:20 am

but GT seems to have edge in blade design, which are designed to cope back pressure better and giver higher static pressure, this according scythe themsleves. Its just hard to verify at home...

b_rubenstein · Post by **b_rubenstein** » Wed Aug 05, 2009 5:21 am

I would assume that the voltage/current/RPM specs are for the fans working in free air. For another data point I looked up the current draw for the S-Flex E: 0.15A @ 1,200 RPM.

Below is a small chart comparing the current, CFM, power used and efficiency for the three fans (based on published specs.)

__________I____CFM____Watts_____CFM/W
GT_____0.034____37_____0.41______90.69
S-Flex__0.15_____49 _____1.80 ______27.22
SS_____0.26____68.5_____3.12______21.96

The efficiency is determined by the motor (electrical) and fan design. Those factors are going to swamp the effects of differences in friction in bearing design. For new fans, there is probably almost no difference in friction. After 50k hrs of service the better bearings in the GT and S-Flex would probably manifest themselves in lower friction and less noise.

People tend to place too much emphasis on theoretical advantages of different technologies when it's the implementation of the technology in specific designs that's more important.

Wayne Redpath · Post by **Wayne Redpath** » Wed Aug 05, 2009 7:38 am

"Do bearings really matter this much?"

Good bearings are quiet and bad bearings can make a lot of unpleasant noise. After lowering the blade noise then the bearing noise may show itself.

"is there something I have missed?"

I've never experienced any fans to have a perfectly linear relationship of rpm to voltage and certainly fan models can be very different from each other. Your quest is that of many others that look to this site for advice. To get the PC reasonably quiet and non-annoying you have the challenge of matching fan characteristics to the mainboard's variable speed fan controller or use fixed voltage operation. There are many excellent fan tests on this site.

Also, there is a good review of fans here:
=> http://xbitlabs.com/articles/coolers/di ... undup.html

The GT's here:
=> http://xbitlabs.com/articles/coolers/di ... html#sect0

Very good comparison charts here:
=> http://xbitlabs.com/articles/coolers/di ... html#sect0

I hope this has been helpful in answering your questions.