reversing fan leads to reverse air flow?

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shegeek72

I just reversed two case fans to see if that would make a HD (Maxtor
w/temp monitor) run cooler and it didn't - it runs hotter. The fans are
in the front of the case, so I had to pull the front cover off which,
as anyone knows who works on puters, can be a hassle. The leads are
much more accessible - can I just reverse them to make the fans spin in
the opposite direction?
 
shegeek72 said:
I just reversed two case fans to see if that would make a HD (Maxtor
w/temp monitor) run cooler and it didn't - it runs hotter. The fans are
in the front of the case, so I had to pull the front cover off which,
as anyone knows who works on puters, can be a hassle. The leads are
much more accessible - can I just reverse them to make the fans spin in
the opposite direction?
Click to expand...

With 2 leads, sure no big deal. With 3 or more, you've got to find the
correct pair. Though it's been easier for me to pull case covers than
it is to re-splice connectors.
 
shegeek72 said:
I just reversed two case fans to see if that would make a HD (Maxtor
w/temp monitor) run cooler and it didn't - it runs hotter. The fans are
in the front of the case, so I had to pull the front cover off which,
as anyone knows who works on puters, can be a hassle. The leads are
much more accessible - can I just reverse them to make the fans spin in
the opposite direction?
Click to expand...

That will make the fans spin in the opposite direction, but the airflow
will not be very good. Fans have curved blades, and are designed to be
more efficient spinning forward than backward.
 
shegeek72 said:
I just reversed two case fans to see if that would make a HD (Maxtor
w/temp monitor) run cooler and it didn't - it runs hotter. The fans are
in the front of the case, so I had to pull the front cover off which,
as anyone knows who works on puters, can be a hassle. The leads are
much more accessible - can I just reverse them to make the fans spin in
the opposite direction?
Click to expand...

It seems to be virtually impossible to find a simple circuit for
what is inside a fan hub. And believe me, I've tried searching for
it several times, and each time I end up wading in a sea of multiphase
motors instead.

This chip UGN5275K from Allegro Microsystems, is an example of a controller
for a brushless DC motor. The chip senses the magnetic field as the fan
rotates, and switches its outputs to cause the fan to rotate in the
preferred direction. Such a chip takes the place of a commutator (that
thing that throws sparks in your electric drill).

http://www.tranzistoare.ro/datasheets2/10/100554_1.pdf

The chip is *unipolar*. That means you *cannot* reverse the power to it,
or you get the "magic smoke". Unless there is a diode in the path, to
prevent damage, in which case there would be no damage, but no rotation
either. And no manufacturer is going to spend $0.05 to protect a fan
from abuse (diode D3 in the diagram in the datasheet, is the protection
against reverse polarity, but no cheap fan would have one).

There may be other ways to control a brushless DC motor, but presumably
as long as there are semiconductors inside, there is going to be that
unipolar thing again.

To reverse the direction of air flow, means removing the fan, and causing
it to point the other way.

With a DC motor that has brushes, and throws sparks, there are no
semiconductors in there to mess things up. One of those, you could
reverse. But not the fan in your computer, as it is too clever for
that.

That is all the info I've been able to find.

Paul
 
You might be better off if you can locate the make, model, specifications
and dimensions of the fan and find a replacement that has greater air flow
(usually more noise also) and upgrade to a higher output model.

JS
 
It depends on the motor but most likely not.
Why not simply remove the motor in install it the other way?

Why reverse it anyways?
Are there other fans on the case other than these two?

Generally fans on the from should suck in while back should blow out.
You do not want all in or all out.
 
The 5 80mm fans in my case can be mounted blowing in or blowing out, and are
reversible..
So, there is no real need to monkey around with wiring at all, keeping in
mind the possibility of shorting out something, at the very least the fan or
at worst the mobo or yourself..
You basically want to bring in the cool air (outside the case) and blow out
the warm air (in the case), fans in the front bring in the air (blowing it
over the HDD's and RAM), while fans in the rear of the case, blow warm air
out, a side fan usually (bringing in additional air) blows into the case,
dispersing heated air @ the display card and or chipsets..
Cheers
j;-j
 
Probably not.

All of the case fans I've seen use brushless DC motors, which only spin in
one direction.

Address scrambled. Replace nkbob with bobkn to reply.
 
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