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AC Fan really sucks (in the good sense)

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dgk

Member
Joined
Feb 2, 2001
Location
Delray Beach FL
Well I replaced my 12V DC 80mm case fan (rear of case, exhaust) with an 80mm AC fan (from Radio Shack). Unfortunately, I violated the laws of scientific experimentation by cutting out the grill at the same time. So I can't swear that the vast improvement in airflow is just the fan, but probably most of it is.

The rating on the fans isn't that different (26 for the DC to 33 for the AC) but the difference in airflow is astonishing. You could fly a glider in the flow coming out of that case.

One problem is that the air inflow (from the front bottom DC fan) isn't keeping up. The airflow from the power supply fan (exhaust) is just about dead. I mean, all the air is coming out of the new fan right below it. I fear that the inside of the case is now a vacuum and I think I'll open up a slot just to let some air come in. The one below the video card is a good bet.

Advantages to the AC fan:
1) No current draw through the power supply or MB
2) Astonishing air flow

Disadvantages:
1) No rpm monitoring
2) Need to make sure it's on.
3) A little louder

I have it hooked up to the surge protector so it goes on when the computer goes on.

Report Ends Here.
 

Metaxas

Senior Member
Joined
Dec 25, 2000
Running an AC fan that close in proximity to your boards is REALLY BAD. AC funs use brushed motors, which create a CRAP load of electrical noise. Just stick a radio up to it on the AM band. I don't mean to shoot your idea down, but you REALLY should consider going back to a DC fan, its safer that way. Not to mention, it could cause instability out da booty. :)
 

stool

Senior Member
Joined
Dec 20, 2000
Location
Albany, NY
Metaxas is right about interference. There is an option, however. If you can, try to get ahold of some snapbead ferrites, and put them on your leads to the AC fan. By the way, you didn't mention your intake fan, but if you have the room, go with a 120mm. Although this won't give you a balanced flow, it will ensure that your intake is better.
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
I don't know where you guys get your AC fans, but I've got a big box full of them. Rotrons, Daytons, Pabsts, Fascos, etc. and not a single one of them use brushes. Some use a motor start capacitor to shift the phase, but no brushes. In 30 years of electronincs, I've never seen an AC fan with a brush. Plenty of DC ones with brushes though modern technology provides most DC fans without brushes now. Yes, AC fans can have a field around them, but you can get them with shaded poles also.
 
OP
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dgk

Member
Joined
Feb 2, 2001
Location
Delray Beach FL
I haven't noticed any problems with the AC fan. In fact, I did it because of a suggestion on another post on general cooling tips. How do I know if my fan has brushes or is producing electrical noise? Oh, hold an AM radio near it. I'll probably have to rip it out of my car...
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
If you put an AM radio next to an open PC, I guarantee you will hear more than just the fan. PCs are excellent sources for RFI, even with the case closed. Put a Spectrum Analyzer pickup near one and see all the spurs and birdies. It's just the nature of square waves being harmonic rich.

That was funny about the car :)

Hoot
 

Metaxas

Senior Member
Joined
Dec 25, 2000
Hoot (Mar 03, 2001 01:42 p.m.):
I don't know where you guys get your AC fans, but I've got a big box full of them. Rotrons, Daytons, Pabsts, Fascos, etc. and not a single one of them use brushes. Some use a motor start capacitor to shift the phase, but no brushes. In 30 years of electronincs, I've never seen an AC fan with a brush. Plenty of DC ones with brushes though modern technology provides most DC fans without brushes now. Yes, AC fans can have a field around them, but you can get them with shaded poles also.


Really? I didn't know that you coudl get stuff like that. Hmmm...nifty. :)
 
W

William

Guest
just remember for optimum airflow, the air coming in must equal the airflow coming out. Stupid rule but we all tend to forget this all the time.
 
OP
D

dgk

Member
Joined
Feb 2, 2001
Location
Delray Beach FL
dunno260 (Mar 03, 2001 09:59 p.m.):
just remember for optimum airflow, the air coming in must equal the airflow coming out. Stupid rule but we all tend to forget this all the time.

Doesn't the outflow have to equal the inflow? I guess if the case implodes, no.