I have a Dell Dimension 4550, 3.06Ghz. CPU has heat sink with no fan attached. The only fan other than the power supply is a case fan that is hooded to the cpu/heatsink.

The JMC/Datech DS9238-12HBTL case fan specs are 1100-5100 RPM, 100 CFM and 51 DB at DC12V 1.50A. Does the fan normally/mostly run at 1100 RPM and only go up 5100 RPM when needed? Is there any (many) RPM range(s) in between? Meaning does it ever run at say 2,000 or 3,000 RPMs for a long time or does it just go from 1100 to 5,000 ( 2 speeds)?

Does the CFM work the same way, is it 100 CFM when it kicks up to 5100 RPM and is it say at 50 CFM when it's only 1100 RPM?

Does going with the same model fan except going from 1.5A to 1.7A make that much difference in the noise?

Is it a good idea to replace this fan with a Panaflo FBA09A12L1A, 2100 RPM and 42.7 CFM. It is less than half the CFM than the JMC and does not seem to be variable speed. But if the JMC is not at 100 CFM all the time does it really matter?

I know that no one probably has this exact same fan but a general answer to those questions would help. I am assuming most thermal fans work the same way. Thank you for any answers!:)

Judging by the specs, it looks like it starts at 1100 rpm - a nice slow speed IMO - and ramps up to 5100 rpm as it gets warmer. At what point the speed increases and how it ramps up who knows? If it's any comfort, most of the fans I know of increase the rpm relative to the temp - ie. infinitely small steps.

The relationship between rpm and cfm is complicated and beyond my grasp, but there is one. The charts on this page should be useful: http://www.cpemma.co.uk/index.html

The datasheet doesn't mention anything about thermal control. Can you see if the fan has a little thermister jutting out anywhere?


Prolly not very. That's only a 13% increase in current.


This may depend on how your fan is controlled. Is there a thermister somewhere?

Thank you for the answers. I do not see any thermal control on it anywhere. I was just assumimg it had as I saw another JMC fan in the "interesting fans recommened list". It seems to be close to the same fan I have:

"JMC 9232-12HB TL 92 x 32 This wolf can produce 82 CFM and a noise level of 45 dBA, but being thermistor controlled, is fairly quiet at 12V and 25C. It will start at 7~8V, be nearly as quiet as most of the quiet fans, yet can ramp up to over 50CFM at that voltage if temperature goes high enough. Useful for high power range PC. See other thermal models in JMC lineup. Dec 24/02"

Anyway, from reading I realize now that I can't go with the Panaflo FBA09A12L1A as I need rpm sensing on the the Dell motherboard. I unplugged my fan and XP would not start up without it. I am now looking at a Pabst 3412N/2GL from siliconacoustics although I am a bit worried that the 35.9 CFM will not be sufficient.

I don't believe the figures..

I have a JMC 92mm fan the low volume one and is said to blow 40cfm at 12v. That's nonsense my panaflo feels like it blows more air at 12v and also at lower voltages. Take manafacturer's specification with a pinch of salt. I found the low volume JMC fan is not to be what it is said to be, fairly quiet and blows a lot of air. hmmmm

Anyway the main source of noise in fans is air turbulance, the more air it blows the more likely it is to be loud inside a computer.

If the Dell BIOS allows it, you can disable the "no cpu fan" error. Look around in the BIOS for this feature.

In your other thread, that little blue nub juttting out downwards from the rotor housing is the thermister. This makes things a little more complicated. In short, you should (dare I say it, you'll need to) get a fan that also has thermal control. More later...

oh good, thank you for noticing that! Ithought it would be on the outer side of the fan, not in the middle... I was very close to buying the wrong replacement fan too.

ok now, I was just looking at the Papst 3412N/2GL w/NMT-2 from http://www.siliconacoustics.com/papst3412n2gl1.html. What do you think about that one (other than the prioce;) ). I am having a hard time finding anything quieter with a thermister.

Also just curious, why would need to replace my fan with a thermister controlled one? The pc/cpu would know the difference?

Ralf, the Dell Bios does absolutley nothing. It is made propriertary for Dell (like almost everything else on this darn computer) and is as basic can be. I'm lucky I can even change the bios clock settings:) hehe

Even the soundblaster card does nork without Dells modified soundblaster driver. I can't just go to the soundblaster website and use their drivers. I and others in the Dell forum have tried.....

Sorry to waste everyones time on here with this junk....

I think I need to rethink my previous reply. Before you can even consider getting a new fan (whether it be regular or thermally controlled), you'll need to get an idea of how much cooling headroom you can afford to sacrifice. I'd start with getting a utilty that can monitor your temperatures. Speedfan, Fanspeed and Motherboard Monitor (MBM) are the 3 utitlties that come to mind. Go to the software section of the Useful links page to download.

Once you get that far and have one of those utilities monitoring your CPU temps, you cans begin to figure out how slow of a fan you can pick.

powergyoza, I have tried motherboard monitor in this pc as well as my older 1.7gb Dell and all it picks up in the dashboard is the cpu. The Dells have no sensing built in whatsoever. I also just d/l and tried both Fanspeed and Speedfan. Fanspeed did not show anything and Speedfan at least gave me my hard drive temp.

I called Dell yesterday and asked them to send me the 1.5A ito replace the 1.7A fan. As I noted in another post, it's the same model # fan, but the part # is different and the 1.5a for some crazy reason is much quieter in the other 2 exact same computers.

So they overnight delivered the fan, but it is the wrong one. The one they sent was the 9232-12HBTL (I wanted the DS9238-12HBTL). I think it's the exact same one that Mike C has in the iteresting recommended list. I like it though, it is pretty quiet. I did notice the air comes out a bit warm compared with my old fan which was cool. The hard drive temp also went up from 34c to 37c, which seems ok. So I think I'm gonna forget about the Pabst for now and keep this one (and it was free too). Anyway I have another problem to worry about now, my Tivo fan or hardrive is making a slight whistling noise.. arggg!! Onto the Tivo forums I go!