Alternating current question.

BrianW · 01-14-2003, 01:44 AM

I am interested in getting a couple high cfm AC fans to make a negative pressure enclosure for water setup. Here is one I am considering: http://www.comairrotron.com/acfans/CaravelAC.htm

Question: I will not want to run these fans at full voltage 110 i guess. I need a way to throttle them down. What is the way to do this?

Thanks in advance.

Brian W

Feopathy · 01-14-2003, 05:43 AM

Hi Brian
The simplest way to do that is to just use a light dimmer switch :-P, believe it or not. It's by no means perfect but it does work as i was trying one the other day on my radial fan's from an old shop heater. The method before in the heater was just several large resistors which is a very primitive, wastefull way of doing it and generates a lot of heat.

bigben2k · 01-14-2003, 08:48 AM

Try to get in touch with Airspirit on this one: he's done something similar.

The dimmer may or may not work, it depends on the design of the AC motor.

BrianW · 01-14-2003, 03:26 PM

Thanks for the replys. I was thinking a dimmer would work as well. BTW I looked at that fan and realized it was really poor as far as static pressure is involved. I'll look into their other offerings. I really want to go AC , seems those fans are more effecient when you compare cfm to dba.

Thanks.

Brian W

Razor6 · 04-01-2003, 07:10 PM

I have an old dimmer on a 120v ac fan and the control is very non linear. Only the first third of the turn is usable. Something to keep in mind.

bigben2k · 04-01-2003, 09:03 PM

Ah! A fellow Houstonian! Welcome!

You're 2 1/2 months late...but I've had the same experience: a light dimmer is only usable on the top third of the turning range, with an AC fan motor. That's because the voltage drops too low for the motor to use it. Note however that the current still flows through it... so if you're not using it, turn it off!

ezlid · 04-02-2003, 12:10 PM

BrianW - AC fans are tricky when trying to control speed with a dimmer switch. A single speed fan only has one winding, while multi-speed fans have multiple windings, one for each speed. I noticed the link was for a 10 inch fan. You would be better off getting a cheap (less than $10) 3 speed desk fan at Walmart, Target, etc. Toss the bits you don't need and go from there. You also might have to make some sound suppression because it might be a tad noisy.

??? - Why buy a 550 CFM fan if you are going to throttle it back? You might be be better off using a lower-rated AC fan. Less noise, less $'s and no need to fool with speed control. Just a thought.

01-14-2003, 01:44 AM	#1
BrianW Cooling Savant Join Date: Jun 2001 Location: Desert City in California Posts: 631	Alternating current question. I am interested in getting a couple high cfm AC fans to make a negative pressure enclosure for water setup. Here is one I am considering: http://www.comairrotron.com/acfans/CaravelAC.htm Question: I will not want to run these fans at full voltage 110 i guess. I need a way to throttle them down. What is the way to do this? Thanks in advance. Brian W __________________ Water Cooled Inwin Q500 (Dual Rads: Rad1 = DTEK Pro Core \| Rad2 = Blick Ice Estreme, Hydor L30, Dangerden Maze2, Bay Res Typhoon Reservoir, 1/2 " DD Tygon Thick Wall Hose). Flow: Res, Pump, CPU watervlock, Y into both rads, both rads into res independently. Athlon XP 1800+ (@ 1731 - 150mhz fsb.), on a Asus A7N266-c, and a Radeon 9000 waiting for RMA'd Saphire 9800 ultra from Newegg) Last edited by BrianW; 01-14-2003 at 02:21 AM.*

01-14-2003, 08:48 AM	#3
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Try to get in touch with Airspirit on this one: he's done something similar. The dimmer may or may not work, it depends on the design of the AC motor. __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

01-14-2003, 03:26 PM	#4
BrianW Cooling Savant Join Date: Jun 2001 Location: Desert City in California Posts: 631	Thanks for the replys. I was thinking a dimmer would work as well. BTW I looked at that fan and realized it was really poor as far as static pressure is involved. I'll look into their other offerings. I really want to go AC , seems those fans are more effecient when you compare cfm to dba. Thanks. Brian W __________________ Water Cooled Inwin Q500 (Dual Rads: Rad1 = DTEK Pro Core \| Rad2 = Blick Ice Estreme, Hydor L30, Dangerden Maze2, Bay Res Typhoon Reservoir, 1/2 " DD Tygon Thick Wall Hose). Flow: Res, Pump, CPU watervlock, Y into both rads, both rads into res independently. Athlon XP 1800+ (@ 1731 - 150mhz fsb.), on a Asus A7N266-c, and a Radeon 9000 *waiting for RMA'd Saphire 9800 ultra from Newegg)

04-01-2003, 09:03 PM	#6
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Ah! A fellow Houstonian! Welcome! You're 2 1/2 months late...but I've had the same experience: a light dimmer is only usable on the top third of the turning range, with an AC fan motor. That's because the voltage drops too low for the motor to use it. Note however that the current still flows through it... so if you're not using it, turn it off! __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

01-14-2003, 05:43 AM	#2
Feopathy Cooling Neophyte Join Date: Jan 2003 Location: Cornwall Posts: 1	Hi Brian The simplest way to do that is to just use a light dimmer switch :-P, believe it or not. It's by no means perfect but it does work as i was trying one the other day on my radial fan's from an old shop heater. The method before in the heater was just several large resistors which is a very primitive, wastefull way of doing it and generates a lot of heat.

04-01-2003, 07:10 PM	#5
Razor6 Cooling Savant Join Date: Apr 2002 Location: Houston, TX Posts: 192	I have an old dimmer on a 120v ac fan and the control is very non linear. Only the first third of the turn is usable. Something to keep in mind.

04-02-2003, 12:10 PM	#7
ezlid Cooling Neophyte Join Date: Sep 2001 Location: Houston, TX Posts: 55	BrianW - AC fans are tricky when trying to control speed with a dimmer switch. A single speed fan only has one winding, while multi-speed fans have multiple windings, one for each speed. I noticed the link was for a 10 inch fan. You would be better off getting a cheap (less than $10) 3 speed desk fan at Walmart, Target, etc. Toss the bits you don't need and go from there. You also might have to make some sound suppression because it might be a tad noisy. ??? - Why buy a 550 CFM fan if you are going to throttle it back? You might be be better off using a lower-rated AC fan. Less noise, less $'s and no need to fool with speed control. Just a thought.

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