undervolting fans. cfm/volt?

zoson · 10-21-2003, 09:01 AM

I'm wondering if anyone has done any quantitative testing on the effects of undervolting fans and the relationship between the voltage supplied to the fan and the cfm output of the fan.
Is the relationship linear? e.g. a 100cfm fan dropped from 12v to 7v is about 59% the power of the fan, so would that mean that the fan is producing now 59cfm?
-Zoson

pHaestus · 10-21-2003, 11:00 AM

Nothing quantitative, but it seems to me that the pressure output of the fan decreases rather more than predicted with linear relationship. P-Q curves as a function of voltage would be MOST helpful; bug JoeC at overclockers about it as he is setup to do something like that now.

BillA · 10-21-2003, 11:14 AM

the mfgrs of fans reted 6 - 14V sometimes have P-Q curves showing the output at 2 or 3 voltages
not linear at all

jaydee · 10-21-2003, 12:59 PM

I don't see how it could be linear. The faster the blade is spinning to more resistance it will incounter from air. The slower it turns the less resistance it will incounter by air.

As an example (not real numbers):

Say it takes 12V to get 100CFM

It may only take 5V to get 50CFM being there is less resistance.

OR this shows how little I know about airodynamics.

Or airodynamics may not even play a part.

I will go back to shutting up now......

sevisehda · 10-21-2003, 03:07 PM

Its not all about voltage. The fans I use pull 1.5A at 12V. I was expecting this to go up as I dropped the voltage. Surprisingly it also dropped. At 5v they only pull 0.3A. So at full power they use 18W however I run them at 1.5W. I don't have any solid number but I would guess they are moving roughly half the aiur they used too.

macklin01 · 03-11-2004, 08:25 AM

Hmm, not sure about airflow, but I do know that the RPMs follow a linear relationship (although not with slope such that halving voltage halves the RPMs.)

So, if anybody else has a relationship between RPMs and CFM, it might be possible to string together a better relationship. (But I agree that by the P-Q curves, it is probably not going to be linear.) -- Paul

DeadEye · 05-09-2004, 10:52 AM

Some useful info
Fans List

10-21-2003, 09:01 AM	#1
zoson Cooling Savant Join Date: Nov 2001 Location: X Posts: 204	undervolting fans. cfm/volt? I'm wondering if anyone has done any quantitative testing on the effects of undervolting fans and the relationship between the voltage supplied to the fan and the cfm output of the fan. Is the relationship linear? e.g. a 100cfm fan dropped from 12v to 7v is about 59% the power of the fan, so would that mean that the fan is producing now 59cfm? -Zoson __________________ Core i7 930 @ 4254Hz 22x193 \| ASUS R3E 901 BIOS \| 12GB Mushkin Blackline 3x4GB @ 1547MHz 7-8-7-24-1N \| Lian Li PC-A10B 2x EVGA GTX275 SLI @ 720/1266/1566 \| 2x 80GB Intel X25-M G2 SSD Raid 0 \| 3x 1TB Samsung Spinpoint 7.2K Raid 5 \| Corsair 950TX H2O \| Enzotech Sapphire Rev.A \| EK-FB RE3 \| Swiftech - 2x MCW60/GTX275 Unisink, MCP655b, MCRes Micro.v2 \| 3x HWLabs SR1-120 あなたの神への弓 Time isn't wasted, when you're gettin' wasted.

10-21-2003, 03:07 PM	#5
sevisehda Cooling Savant Join Date: May 2003 Location: NY Posts: 234	Its not all about voltage. The fans I use pull 1.5A at 12V. I was expecting this to go up as I dropped the voltage. Surprisingly it also dropped. At 5v they only pull 0.3A. So at full power they use 18W however I run them at 1.5W. I don't have any solid number but I would guess they are moving roughly half the aiur they used too. __________________ CPU: Barton2500 @ 2.43 ghz MB: NF7S Rev2 RAM: 2x 256mb Kingston HyperX 3500 HD's: 2x 160gb SATA RAID GPU: Sapphire X800Pro VIVO -> XT Plat(softmod) 520/590

03-11-2004, 08:25 AM	#6
macklin01 Cooling Neophyte Join Date: Feb 2004 Location: overclockers.com Posts: 5	Hmm, not sure about airflow, but I do know that the RPMs follow a linear relationship (although not with slope such that halving voltage halves the RPMs.) So, if anybody else has a relationship between RPMs and CFM, it might be possible to string together a better relationship. (But I agree that by the P-Q curves, it is probably not going to be linear.) -- Paul __________________ New Computer: (computational biophysics and chemotherapy simulation) P4 3.0C @ 3.3 GHz / Abit AI7 / 2 x 512 MB PC3500 Recent Post-Processing & Fun Computer: PIII 1.26-S GHz @ 1425 MHz / Shuttle AE25 / 512 MB Kingmax PC150 Samsung DVD-CDRW / Abit Ti4200 128 MB / Creative SBLive! 5.1 My heatware (macklin01)

10-21-2003, 11:00 AM	#2
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Nothing quantitative, but it seems to me that the pressure output of the fan decreases rather more than predicted with linear relationship. P-Q curves as a function of voltage would be MOST helpful; bug JoeC at overclockers about it as he is setup to do something like that now.

10-21-2003, 11:14 AM	#3
BillA CoolingWorks Tech Guy Formerly "Unregistered" Join Date: Dec 2000 Location: Posts: 2,371.493,106 Posts: 4,440	the mfgrs of fans reted 6 - 14V sometimes have P-Q curves showing the output at 2 or 3 voltages not linear at all

10-21-2003, 12:59 PM	#4
jaydee Put up or Shut Up Join Date: Dec 2001 Location: Spokane WA Posts: 6,506	I don't see how it could be linear. The faster the blade is spinning to more resistance it will incounter from air. The slower it turns the less resistance it will incounter by air. As an example (not real numbers): Say it takes 12V to get 100CFM It may only take 5V to get 50CFM being there is less resistance. OR this shows how little I know about airodynamics. Or airodynamics may not even play a part. I will go back to shutting up now......

05-09-2004, 10:52 AM	#7
DeadEye Cooling Neophyte Join Date: Apr 2004 Location: Nr Oxford, UK Posts: 41	Some useful info Fans List

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