Ongoing saga of the case fan

So, as I said before I had another fan failing and from the replies I
received about which fan to buy I purchased a Noctua fan with 3 wires
which was what the case fan had.

Lo and behold when I tried to install it the existing fan had a 3 wire
fan with a 4 wire receptacle on the end which meant my new 3 wire fan
would not fit. Even if I bent a wire over on the MB -which I would
never do- the guide on the side of the receptacle would not match with
the new fan. Different width.

I have 4 wires on the MB so what would happen if I installed a 4 wire
fan which would probably fit but I am concerned about an unanticipated
bad happening. I don't like bad surprises.

I appreciate any help.

south walker
mega 1999

On 01/24/2019 7:32 PM, swalker wrote:
So, as I said before I had another fan failing and from the replies I
received about which fan to buy I purchased a Noctua fan with 3 wires
which was what the case fan had.

Lo and behold when I tried to install it the existing fan had a 3 wire
fan with a 4 wire receptacle on the end which meant my new 3 wire fan
would not fit. Even if I bent a wire over on the MB -which I would
never do- the guide on the side of the receptacle would not match with
the new fan. Different width.

I have 4 wires on the MB so what would happen if I installed a 4 wire
fan which would probably fit but I am concerned about an unanticipated
bad happening. I don't like bad surprises.

I appreciate any help.

south walker
mega 1999


Well if all the laws of electronics still hold, the 4 wire header on the
MB must be a monitored and speed controlled fan header.
I would exchange the 3 wire fan for a 4 wire and try it, I can't see any
other reason or use for it. But if someone has better info on this
please correct me if I'm wrong, I would not want someone to damage their
gear on my say so alone.

Rene

swalker wrote:

So, as I said before I had another fan failing and from the replies I
received about which fan to buy I purchased a Noctua fan with 3 wires
which was what the case fan had.

Lo and behold when I tried to install it the existing fan had a 3 wire
fan with a 4 wire receptacle on the end which meant my new 3 wire fan
would not fit. Even if I bent a wire over on the MB -which I would
never do- the guide on the side of the receptacle would not match with
the new fan. Different width.

I have 4 wires on the MB so what would happen if I installed a 4 wire
fan which would probably fit but I am concerned about an unanticipated
bad happening. I don't like bad surprises.

The shroud around the 3-wire fan's connector should be narrow enough to
miss the 4th pin in the mobo's header. Was there a shroud also around
the mobo's 4-pin header or was it open (just the 4 pins sticking up with
nothing around them)?

Did you give the mobo's brand and model in your original query? If not,
respondents are going to assume the default of just a 3-pin fan (or even
a 2-pin fan if the BIOS doesn't try to control its speed). With vague
details, expect generic answers.

In your thread titled "Case fan replacement OT", you never identified
the brand and model of your motherboard. Specifics matter. In that
prior fan, *you* said the original fan AND the mobo had only 3 pins. So
what changed to physically alter the mobo header from 3 to 4 pins? Did
you swap out the mobo, too?

3-wire fans use PWM (pulse width modulation) to change the speed of the
fan. The signals a +5V, ground, and RPM sense (FAN_TACH). To change
that fan's speed, its voltage is modified to change its duty cycle (how
long the 5V goes high and how long it is low within one cycle). A
shorter duty cycle (how long 5V is applied) with a cycle means a lower
average voltage over that cycle. A longer duty cycle means the 5V is
high during more of the cycle meaning an average higher voltage during
that cycle. That assumes the 5V power line can be modified regarding
its duty cycle and that requires a controller on the mobo. 4-wire fans
have a line for RPM sense (FAN_TACH) to monitor the speed of the fan and
another line (FAN_CONTROL) to specify RPM to the fan. Its voltage
remains constant at 5V and it is the fan that is told what RPM to run
at. 3-wire fans need no logic within but do have to operate with a
fluctuating 5V line. 4-wire fans have internal logic that communicates
with the mobo over the FAN_CONTROL line to have the fan itself decide
what RPM to spin at.

If you connect a 3-wire fan to a 4-pin header on the mobo (might require
prying off the polarization shroud around the mobo header), and since
that header is designed for regulating fan speed by telling it via
FAN_CONTROL what speed to run (but you won't be using that pin) and
won't use PWM for that header, the 3-wire fan will run at full speed.
The fan will report its RPM using the FAN_TACH line but has no means of
regulating the fan's speed since it won't use PWM on that header and you
didn't use the 4th pin (FAN_CONTROL).

You started a new and disconnected thread to continue your prior
discussion. After looking up "EVGA Precision XOC", that is not a
separate fan controller, like one that slides into an external drive bay
in the case. Instead it is just a software-based fan controller program
that works with a particular mobo. That means you really should match
the number of pins on the fan to the number of pins on the mobo's header
for that fan.

Don't know from whom you ordered the Noctua fan. I know with Newegg
that I've been able to return parts that were wrong. If it was there
error then there is no restocking fee. If it was my error, there might
be a restocking fee. Plus you'll have to pay the return shipping, so
maybe just keep the 3-pin fan for some other future project, decide to
let it run at full speed by sliding it onto the correct 3 pins of the
4-pin header on the mobo, or return it for a [partial] refund and get a
fan that matches the mobo header.

swalker wrote:
So, as I said before I had another fan failing and from the replies I
received about which fan to buy I purchased a Noctua fan with 3 wires
which was what the case fan had.

Lo and behold when I tried to install it the existing fan had a 3 wire
fan with a 4 wire receptacle on the end which meant my new 3 wire fan
would not fit. Even if I bent a wire over on the MB -which I would
never do- the guide on the side of the receptacle would not match with
the new fan. Different width.

I have 4 wires on the MB so what would happen if I installed a 4 wire
fan which would probably fit but I am concerned about an unanticipated
bad happening. I don't like bad surprises.

I appreciate any help.

south walker
mega 1999

3 wire fans fit on 4 pin motherboard connectors.
You make sure that pin 1 mates with pin 1. The latch
should be on the correct side. The 3 wire fan will
run at full speed, and the RPM (rotation speed) will
work. See how the latch position in this picture, guides
you to the pin 1 end ? The body of the 3 wire connector
should not be so wide that it can't fit.

https://allpinouts.org/img/connector...wm_3to4pin.png

4 wire fans fit on 3 pin motherboard connectors.
The fourth "hole" overhangs the end of the connector.
The latch should be on the correct side. The four
wire fan will run at full speed (since the PWM signal
is floating and not driven). The RPM signal will work.

https://allpinouts.org/img/connector...wm_4to3pin.png

3 wire on 3 pin. RPM works. If mobo has Vfan adjust, speed is adjustable.

4 wire on 4 pin. RPM works. PWM works so speed is adjustable.
This one is more likely to have speed control.

Reference:

https://allpinouts.org/pinouts/conne...cpu-4-pin-fan/

Paul

"swalker" wrote in message
...
So, as I said before I had another fan failing and from the replies I
received about which fan to buy I purchased a Noctua fan with 3 wires
which was what the case fan had.

Lo and behold when I tried to install it the existing fan had a 3 wire
fan with a 4 wire receptacle on the end which meant my new 3 wire fan
would not fit. Even if I bent a wire over on the MB -which I would
never do- the guide on the side of the receptacle would not match with
the new fan. Different width.

I have 4 wires on the MB so what would happen if I installed a 4 wire
fan which would probably fit but I am concerned about an unanticipated
bad happening. I don't like bad surprises.

I appreciate any help.

south walker
mega 1999

A 3-pin fan will work on a 4-pin MB connector, and a 4-pin fan will work on
a 3-pin MB connector:
https://allpinouts.org/pinouts/connectors/motherboards/motherboard-cpu-4-pin-fan/

Notice the tab on the MB is offset to allow the 3-pin fan to only connect to
pins 1, 2, & 3. The guides on a 4-pin fan plug are offset also to allow it
to go on only 1 way.
HTH.
--

SC Tom