Power Supply Fan

  • Thread starter Thread starter Renaldo
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Renaldo

The 120mm fan in my power supply just went kaput. ...on the hottest day
of the year too, who woulda thunk it?

It has two little wires leading to a 12v connection on the power supply's
circuit board.

I want to order a new 120mm fan and replace the broken junk. However,
all the 120mm 'case fans' that I looked at have 3 wires instead of 2.

Why three wires? Is it something to do with variable speed control?

Can I just snip the connector and splice 2 of the wires to the junk fan's
connection (and ignore the 3rd wire)?

Anyone know any details? Like: what do the wire colors mean and such?

Thanks for any replies.
 
in message
The 120mm fan in my power supply just went kaput. ...on the hottest
day
of the year too, who woulda thunk it?

It has two little wires leading to a 12v connection on the power
supply's
circuit board.

I want to order a new 120mm fan and replace the broken junk. However,
all the 120mm 'case fans' that I looked at have 3 wires instead of 2.

Why three wires? Is it something to do with variable speed control?

Can I just snip the connector and splice 2 of the wires to the junk
fan's
connection (and ignore the 3rd wire)?

Anyone know any details? Like: what do the wire colors mean and such?
Click to expand...


2 wires (red & black) are for power and ground. 3rd wire (yellow) is
the sense (for RPM). In the PSU, check if the fan is connected using a
pin header and connector or if it is soldered into the PCB. If soldered
in, cut the wires near the hub of the old fan so you can splice them
onto the wires for the new fan (i.e., cut off the 3-pin connector on the
new fan, splice the same-colored wires together, and just tape up the
3rd wire against the other 2 wires). The fan will function just fine if
the RPM sensor is not connected.

However, since you don't know what color is for power, ground, and sense
or that the 3rd wire is for speed sense then it is also likely that you
don't have the skills to replace the fan, especially if soldering is
needed. Ask a geek friend or have a shop do it. Some PSUs actually do
use a speed sense on the PSU fan but usually that is for the bottom and
redundant fan while the rear fan is constant speed.
 
The 120mm fan in my power supply just went kaput. ...on the hottest day
of the year too, who woulda thunk it?

It has two little wires leading to a 12v connection on the power supply's
circuit board.

I want to order a new 120mm fan and replace the broken junk. However,
all the 120mm 'case fans' that I looked at have 3 wires instead of 2.

Why three wires? Is it something to do with variable speed control?

Can I just snip the connector and splice 2 of the wires to the junk fan's
connection (and ignore the 3rd wire)?

Anyone know any details? Like: what do the wire colors mean and such?

Thanks for any replies.
Click to expand...

the 120mm case fan's 3rd wire is to do with sensing. I think it just
sends the RPM speed to the MBRD so the BIOS can read the speed and
display it. You don't even need it when installing it as a case fan.
(note- this is quite well known 'cos there are adaptors that play with
that fact. Converting the 3 pin to a 4 pin molex, and i've even seen
an adaptor converting the 3 pin into a 4 pin molex, with a 3 pin
connector with just the sensor wire. Every case fan seems to come with
such a thing)

The way it works .. is the 3 wires coming from a fan, are colour
coded.. One is + (it takes 12V I think), one is GND, one is sensing.
Black one is always GND or - (not sure which you'd call it). And from
what I remember.. The + is usually red. And the sensing one is
yellow.

You could always check yourself, one way would be to plug the fan in,
so it starts spinning, gets some DC running through it. Cut all the
wires(don't need to cut the black though). Hold the black 'cos it's
necessary. Then hold one other wire and when it works, you know that
one is the + one, 'cos that one is necessary.

It sounds like you know what to do, but you just didn't know which is
the sensor wire. That'd tell you. You're going ot be cutting the wires
anyway so why not.

Just a point incase of any confusion.
The colour coding of wires coming out the power supply is different by
the way. On that one, you have volts coming out them. Red is 5V,
yellow is 12V. Black is GND. You can run a fan at whatever voltage..
using 5V and GND. 12V and GND.. and even a (perhaps not so good for
the power supply), a so-called 7V fan mod. Connect the black fan wire
to 5V. The red or + fan wire to 12V. And it does 12V-5V=7V.
The PSU colour coding is mentioned in scott mueller's pocket UGRP
book, but would be on google too.

they should both be 12V fans. (Fans supporting / designed to run at,
12V! I guess all case fans are. 120mm ones for sure)
 
in message












2 wires (red & black) are for power and ground. 3rd wire (yellow) is
the sense (for RPM). In the PSU, check if the fan is connected using a
pin header and connector or if it is soldered into the PCB. If soldered
in, cut the wires near the hub of the old fan so you can splice them
onto the wires for the new fan (i.e., cut off the 3-pin connector on the
new fan, splice the same-colored wires together, and just tape up the
3rd wire against the other 2 wires). The fan will function just fine if
the RPM sensor is not connected.

However, since you don't know what color is for power, ground, and sense
or that the 3rd wire is for speed sense then it is also likely that you
don't have the skills to replace the fan, especially if soldering is
needed. Ask a geek friend or have a shop do it. Some PSUs actually do
use a speed sense on the PSU fan but usually that is for the bottom and
redundant fan while the rear fan is constant speed.-
Click to expand...

I don't think he'd have to solder anything.
Suppose the PSU fan's 2 wires are soldered into the connector..
He can just cut the wires and connect his new fan's 2 wires onto them.

strip off some of the wires' jacket, the wires will tie together. Wind
the end of the GND wire coming from in the PSU(which was of the PSU
fan), around the end of the GND wire coming from the case fan.
Similarly with the + wire that was of the PSU fan, and is now hanging
out the PSU. It's usually red, even though it has 12V going through
it ';cos it's a wire coming from a fan, just colour coded to indicate
that it's + and not GND or sensor. And attach it to the + wire of
the case fan.

I don't see any soldering necessary.


I'm not an electronics geek, but I managed it. You probably aren't an
electronics geek either! There's no justification for telling him to
go to a shop to get it done!!
 
jameshanley39 wrote in message
I don't think he'd have to solder anything.
Suppose the PSU fan's 2 wires are soldered into the connector..
He can just cut the wires and connect his new fan's 2 wires onto them.

strip off some of the wires' jacket, the wires will tie together. Wind
the end of the GND wire coming from in the PSU(which was of the PSU
fan), around the end of the GND wire coming from the case fan.
Similarly with the + wire that was of the PSU fan, and is now hanging
out the PSU. It's usually red, even though it has 12V going through
it ';cos it's a wire coming from a fan, just colour coded to indicate
that it's + and not GND or sensor. And attach it to the + wire of
the case fan.

I don't see any soldering necessary.
Click to expand...


I'm not a fan of the Red Green Show. For a *good* splice, solder the
twisted ends and use heatshrink or crimp-on wire nuts (not the screw-on
type). Do NOT rely on electrical tape to stay in place over the twisted
ends. Heat and time will unravel that tape and the resultant short
could fry a component in the PSU necessitating its replacement.
 
I don't think he'd have to solder anything.
Suppose the PSU fan's 2 wires are soldered into the connector..
Click to expand...

Although it is rarer on newer PSU with 120mm fan, some PSU
fans' leads are soldered direct to the PSU PCB, there is no
connector.

He can just cut the wires and connect his new fan's 2 wires onto them.
Click to expand...

Yes that is always an option, but ...

strip off some of the wires' jacket, the wires will tie together. Wind
the end of the GND wire coming from in the PSU(which was of the PSU
fan), around the end of the GND wire coming from the case fan.
Similarly with the + wire that was of the PSU fan, and is now hanging
out the PSU. It's usually red, even though it has 12V going through
it ';cos it's a wire coming from a fan, just colour coded to indicate
that it's + and not GND or sensor. And attach it to the + wire of
the case fan.

I don't see any soldering necessary.
Click to expand...

Don't just twist the wires, it is not a reliable connection.
IF you had a good precision micro-crimper and crimps you
could crimp them together instead, also adding an external
insulator if it wasn't integral to the crimp.

I'm not an electronics geek, but I managed it. You probably aren't an
electronics geek either! There's no justification for telling him to
go to a shop to get it done!!
Click to expand...

You really really do not want to create a connection that is
potentially unreliable in a PSU. Suppose the heat in the
PSU causes the electrical tape to unwind and it gets caught
in the fan. Odds are good it'll then pull the wires apart
so you now have bare wires dangling in a part with AC line
voltage & current potential in it.
 
The 120mm fan in my power supply just went kaput. ...on the hottest day
of the year too, who woulda thunk it?
Click to expand...

Lots of PSU use low-end 120mm fans that are prone to be an
early failure point. If it was just the bearing that
seized, you might find you can take the label off, put 2 - 4
drops of thick oil in and gently free up the bearing.
Depending on how bad it was, it might continue running for
years, but it'll at least be likely to keep the system
operational until you can order/receive a decent replacement
fan (ideally not a sleeve bearing fan, rather one clearly
spec'd as "dual ball bearing").


It has two little wires leading to a 12v connection on the power supply's
circuit board.

I want to order a new 120mm fan and replace the broken junk. However,
all the 120mm 'case fans' that I looked at have 3 wires instead of 2.
Click to expand...

Not a problem, just clip off the yellow lead (RPM lead, it's
the wire opposite the black ground wire if looking at a
motherboard 3 pin connector (as typically comes on such fans
from PC parts venders)).

Why three wires? Is it something to do with variable speed control?
Click to expand...

No, Intel did spec variable speed control for a 4 wire fan
but with 3 wires and a fan proposed for a "PC" use, the 3rd
wire is an RPM sensor. However it is possible to find fans
for industrial uses where the fan manufacturer made the 3rd
lead a different function such as a simple binary-reporting
"rotor lock" sense line, or a variable speed control... it's
just that in a PC, nobody (AFAIK) is using 3 pin fans for
variable speed control as the demand for RPM sensing is
higher, plus when the equipment designer wants to control
RPM they can integrated that into the fan power circuit
instead, on the device instead of in the fan.

Can I just snip the connector and splice 2 of the wires to the junk fan's
connection (and ignore the 3rd wire)?
Click to expand...

Yes, just make sure it's cut really short so it can't
contact anything else or get caught in the blade. Getting
more elaborate you could slip a piece of heatshrink tubing
over the cut end, and/or nylon wire-tie it out of the way.
 
Renaldo said:
The 120mm fan in my power supply just went kaput. ...on the hottest day
of the year too, who woulda thunk it?

It has two little wires leading to a 12v connection on the power supply's
circuit board.

I want to order a new 120mm fan and replace the broken junk. However,
all the 120mm 'case fans' that I looked at have 3 wires instead of 2.

Why three wires? Is it something to do with variable speed control?
Click to expand...

I know this doesn't answer your question (but fortunately others seem to
have), but a few years ago when one of my power supplies died (it turned out
to be the fuse, replacing it and it was fine) I received the advice that
power supplies typically have some large capacitors in them that may be
sufficient to kill you if they discharge through you. So if you are dabbling
inside your power supply be sure that its been disconnected long enough for
any residual charge to have dissipated. Personally I'd go out any buy a new
power supply, quicker and easier but not as cheap.

Hope all goes well with your replacement.
 
I know this doesn't answer your question (but fortunately others seem to
have), but a few years ago when one of my power supplies died (it turned out
to be the fuse, replacing it and it was fine) I received the advice that
power supplies typically have some large capacitors in them that may be
sufficient to kill you if they discharge through you. So if you are dabbling
inside your power supply be sure that its been disconnected long enough for
any residual charge to have dissipated. Personally I'd go out any buy a new
power supply, quicker and easier but not as cheap.

Hope all goes well with your replacement.
Click to expand...


On any properly working ATX PSU the caps will have
discharged to a save level in about 15 seconds or less.

It takes about 10 minutes to pull a PSU, heat up an iron and
solder the new fan in, then reassemble and install in the
system again. Most of the time is spend removing the PSU
from the case, reinstalling and rerouting the wires... which
is something you'd have to do anyway if you replace the PSU
with a new one.
 
Thanks for the replies, they were very helpful.

I ended up being able to slip the 3-wire connector onto the 2-pronged 12v
post that was located on the power supply's circuit board. The unused hole
in the connector, which corresponds to the yellow wire (speed sensing
wire), is just hanging off the side, unconnected.

It works fine, the fan is quiet and effective, and I'm relieved and happy.
 
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