Jury-Rigged Fan - Is It Safe?

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Is there anything unsafe about using a fan from an old power supply
box in lieu of a regular 80mm fan? I ripped out a fan from the power
unit on an old machine, and stripped the two wires. I had a look at
the old machine's cpu fan, which plugged into one of the large white
power connectors, so I pulled the two leads out from that connector,
stuck in the two leads from my newly salvaged fan, and plugged it into
my current computer. Well, it works! The thing seems to be a standard
80mm fan, and is working as my new case fine right now.

Is there any way to tell if its doing anything funny to my power
supply or voltages? This was really a shot in the dark, on a computer
I don't much care for, I really have little idea what I'm doing (other
than being well-aware I should not touch anything inside the old
machine's power supply), but it does seem to be working. I'm just
worried my power supply might blow up or something.

Re: Jury-Rigged Fan - Is It Safe?

Temperatures are down. It's mounted in the rear, as an exhaust. How do
I figure out which way the airflow should be going?

Basically there is a side intake with suction pipe that supplies the
cpu fan with airflow, and the rear grille mount for a fan is in the
vicinity of the cpu fan, so I figured exhaust would be good - it
should draw more air through the side intake towards the cpu fan and
it should pull air away from the components below that (video card
etc). I figure if it were mounted as an intake ... it would just be
pulling hot air down from the exhaust on the PSU and blowing it back

There is also a spot for a front fan ... I figure this must be intake?
Would it be better to have it mounted at the front as an intake fan?
Keeping in mind that the only other exhaust is from the PSU.

The fan itself has a sticker on it that says it is 12V, looks just
like a regular 80 mm case fan except it has no connector; it doesn't
seem to have a controller and doesn't show up in Speedfan or things
like Lavalys' Everest diagnostics. It's meant for the inside of a PSU,
and has no connector - I just stripped its two wires and attached them
to 2 pins of a 4-pin internal power connector. On an extension piece,
so the fan can be plugged or unplugged as anything else connected to
the 4-pin power connectors.

Voltage values don't look any different at all with the fan plugged in
or not.

It's probably fine .... I'm just shocked that it was so easy and it

Re: Jury-Rigged Fan - Is It Safe?

Well all fans are fans... but we must take in consideration-:
The working voltage, The amount of air flow and the direction of air
flow...  sometimes little arrow's on the casing shows the direction of
rotation and the direction of airflow.

Obviously you don't want the air flow to be less or things will get
warmer and you want the direction to be right, which can be corrected
by turning the fan back to front - should it be different than the
original one.

Obviously you need to consider the amount of power or current drawn by
the fan, esepcially if driven by a servo speed controller.... yet you
can still use these by 12V rail from the power unit by-passing the

As a temporary measure providing all is within reasonable  proportions
should be ok to get you by.

It's always a good idea to take notes and stick em'  on the inside
cover of the case... temperature and voltage indications (and any
other settings you might need to remember), many a bios screen
indicates these items...

.so you have a datum line to work from should you have any problems
at a later stage... ie sticky fans will cause a temperature rise,
faulty power units fluctuating voltages etc.


Re: Jury-Rigged Fan - Is It Safe?

Oooops yeah computer fans are indeed 12V.

Simply connect it up and hold a tissue near one side and you'll soon
see.... should be able to tell with the palm of your hand. The fans at
the back you'll want it blowing out, if it's at the front it oughta
blow into the case.

I have one on the front blowing in and it does make a big difference
to the case temperature, I keep thinking it would be much better
mounted on the side... but that mean's cutting a hole ~ I find that
boring  :D . Trouble is it helps blow the dust in as well... could
always use a filter of course.

Here's something I dug out for you.

As you mentioned, some fans have four wires... these are just the taco
pulse for RPM speed indication, which can be ignored.


Re: Jury-Rigged Fan - Is It Safe?

Well, it is definately exhausting air out and I definately have
reduced temperatures. It's been running 24hrs and no problems.

Reduce, reuse, recycle! I don't think I'll even bother getting a
proper fan ... this seems to be a standard, 80mm 12V fan, it probably
has an analogous case fan model, the only difference being the
connectors. As long as there is no risk of fire from the way I have
hooked it up, I can't foresee any problem.

I know I'm only saving $5 but it's the principle, I like the idea of
harvesting old computers for parts. I think I might get a fan to mount
at the front though ... just to create more of a wind tunnel. The
problem I originally had was this crappy video card I got, that has no
fan (just a heatsink) and was giving me corruption .... someone
suggested it was probably overheating so I did this ... haven't had
the problem since.

About filters ... how much do filters reduce airflow? We have 3 cats,
so I am always cleaning this thing out.

Re: Jury-Rigged Fan - Is It Safe?

Filters, they'er kinda sponge or woven type thin pad the size and
shape of the fan made for the purpose, they do stop air flow but it's

The balance is between a slight loss of air flow and the reduction of
dust and of course the cooling ability, obviously you only use these
when the fan is blowing inwards.

I don't use one, it's amazing where the dust comes from though - it
just appears from nowhere, it's microscopic and builds up over time as
you know.


Re: Jury-Rigged Fan - Is It Safe?

On Fri, 23 Feb 2007 11:13:08 -0000, no@spam.invalid (Davy)

Quoted text here. Click to load it

A typical filter panel, particularly the type mounted on a
fan of the same size, has a substantial impact on airflow,
not minimal, not a slight loss.  Because of the great
reduction in flow from any filter medium dense enough to be
worth using (else it just lets in too much dust defeating
the purpose), the ideal is to have a filter area as large as
reasonably possible.  On a case it is typically a large
front sheet, or in a car there is pleating for the same
(area increase) effect.

Re: Jury-Rigged Fan - Is It Safe?

On Fri, 23 Feb 2007 11:13:00 -0000, no@spam.invalid (edges)

Quoted text here. Click to load it

Presuming same voltage, and current low enough to be within
the capability of the supply line, compatible size, it will
work fine.  One of the larger problems with very old fans is
that many were quite crude, poor airflow:noise ratio
compared to modern fans (certainly not all, there were many
good older fans but in the typical old PSU for a "PC", I see
mostly junk fans albeit more hefty than modern junk fans).
The other larger problem is a fan has a finite lifespan,
that lifespan could be mostly over at this point
particularly if it's a sleeve bearing type, though with the
sleeve bearing you can relube it to greatly extend that

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