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From: DanielEKFA on 1 Apr 2008 06:33
Hi there :)

I was hoping someone could help me clarify if this idea I got is a good one
or not. Yesterday, I just got a Thermalright Ultra 120 CPU cooler to which I
can attach two 12-inch fans. I'd like the motherboard (an ASUS P5K-E
WiFi/AP) to be able to throttle these two fans in the same way it did the
stock cooler's fan, so that when the CPU is cool, I get as little noise as
possible, while when it runs hot, it'll throttle up the fans to more
effectively cool down the CPU.

Thing is, it's not like there's two connectors for the CPU cooler's fans,
there's just the one. Now, I was thinking that it might be possible to
simply connect both fans to the same connector. But then I thought, "how
would that affect the fan rotation readings," which, AFAICT, are read
through the yellow wire, while the black and red are ground and +12V
respectively.

Then I start thinking about how this throttling is done in the first place,
and I'm *guessing* that the yellow wire reports back rotational speed in
some way, while some mechanism lowers the voltage (or something equivalent
to that) on the power wires, effectively controlling the fan. So, I'm
thinking I could just share the ground and +12V wires between two fans,
while using just one's yellow wire to report back speed.

Okay, so my questions are the following:
A) Would this work? (I realize that I'd only be able to detect the possible
death of the one fan which is connected to the yellow wire, but as they're
both cooling the same object, I'm willing to accept this)
B) Would the motherboard be able to support this, power consumption wise,
i.e. would I be in risk of blowing out a capacitor or worse? How many watts
would be safe to draw from these onboard connectors?

Thanks in advance for any feedback :)

Daniel

From: GT on 1 Apr 2008 08:45
"DanielEKFA" <danielekfa(a)yahoo.com> wrote in message
news:47f20f97$0$90263$14726298(a)news.sunsite.dk...
> Hi there :)
>
> I was hoping someone could help me clarify if this idea I got is a good
> one or not. Yesterday, I just got a Thermalright Ultra 120 CPU cooler to
> which I can attach two 12-inch fans. I'd like the motherboard (an ASUS
> P5K-E WiFi/AP) to be able to throttle these two fans in the same way it
> did the stock cooler's fan, so that when the CPU is cool, I get as little
> noise as possible, while when it runs hot, it'll throttle up the fans to
> more effectively cool down the CPU.
>
> Thing is, it's not like there's two connectors for the CPU cooler's fans,
> there's just the one. Now, I was thinking that it might be possible to
> simply connect both fans to the same connector. But then I thought, "how
> would that affect the fan rotation readings," which, AFAICT, are read
> through the yellow wire, while the black and red are ground and +12V
> respectively.
>
> Then I start thinking about how this throttling is done in the first
> place, and I'm *guessing* that the yellow wire reports back rotational
> speed in some way, while some mechanism lowers the voltage (or something
> equivalent to that) on the power wires, effectively controlling the fan.
> So, I'm thinking I could just share the ground and +12V wires between two
> fans, while using just one's yellow wire to report back speed.
>
> Okay, so my questions are the following:
> A) Would this work? (I realize that I'd only be able to detect the
> possible death of the one fan which is connected to the yellow wire, but
> as they're both cooling the same object, I'm willing to accept this)
> B) Would the motherboard be able to support this, power consumption wise,
> i.e. would I be in risk of blowing out a capacitor or worse? How many
> watts would be safe to draw from these onboard connectors?

A few things:
1. Why not try the cooler with just 1 fan to start with and see what the
performance is like. That way no wiring will be required.

2. Your assumptions about the yellow wire is correct - an RPM signal. The
BIOS controls the fan speed according to temperature of the CPU. When it
reaches a certain temperature threshold (normally also set in the BIOS), the
fan will speed up until the temperature drops below again.

3. Your solution for wiring 2 fans would effectively wire the 2 fans in
parallel, so they would both run at the same voltage, but you would double
the current required. I can't say whether that would be a problem or not -
that all depends on the circuitry and fusing on the motherboard for the CPU
fan connector. My gut instinct tells me that it would be fine. But, use the
yellow wire from just 1 fan.


From: Angelo Campanella on 1 Apr 2008 09:53
DanielEKFA wrote:
> A) Would this work?

Basically, it's a great ide, but the devil is in the details.

>(I realize that I'd only be able to detect the
> possible death of the one fan which is connected to the yellow wire, but
> as they're both cooling the same object, I'm willing to accept this)
> B) Would the motherboard be able to support this, power consumption
> wise, i.e. would I be in risk of blowing out a capacitor or worse? How
> many watts would be safe to draw from these onboard connectors?

The RPM signal (yellow wire) signal from the second fan might be
terribly confusing and will cause erroneous control. But then it might
not depending on the RPM logic... nobody nows for sure. It is best to
connect black and red wires only to the new fan, and let the new fans
rum at whatever RPM the partial voltage leads them to; no big deal.

If my understanding is correct, the red wire does not see exactly 12
volts but something lower depending on what the control circuit feeds
it. You propose to feed the red wire of the second fan from the red
terminal of the first fan. That assumes that both fans are alike. If
they both expect 12v for full throttle, then it's more likely so. If the
extra fans pull the same current or more curent, then it is likely that
the motherboard power supply will not carry all fans, certainly not at
maximum cooling power. If the new fans require less current than the
original CPU fan, it will likely work just fine.

For new fans drawing more current, a separate current feeding supply
should be installed. If the applied voltage is switched (either 12v or
zero in rapid succession) then your new control circuit is easy and
cool. If it is analog partial voltage, then heat dissipation within your
new control circuit will need to be considered (heat sink, etc). It is
possible that where current switching (full 12 volts, part time) is
used, it is at an ultrosound rate, then smoothed by a capacitor before
being fed to the fan motor. Using this smoothed external signal for your
control circuit results in an analog circuit requiring a heat sink. It
is also possiblte that the switching is at a low frequency, and that you
can use that as a new switched control signal. Put a scope on the 12v
terminal and determine which it is.

Another possibility is to simply run the new fans at one reduced
voltage (e.g. 5 volts), for low RPM silent operation. At least start out
that way. Another possibllty is to run the two new fans in series,
giving 6 volts each for the same result.

Angelo Campanella

From: GT on 1 Apr 2008 10:59
"Angelo Campanella" <a.campanella(a)att.net> wrote in message
news:I7rIj.60503$D_3.29124(a)bgtnsc05-news.ops.worldnet.att.net...
> DanielEKFA wrote:
>> A) Would this work?
>
> Basically, it's a great ide, but the devil is in the details.
>
>>(I realize that I'd only be able to detect the possible death of the one
>>fan which is connected to the yellow wire, but as they're both cooling the
>>same object, I'm willing to accept this)
>> B) Would the motherboard be able to support this, power consumption wise,
>> i.e. would I be in risk of blowing out a capacitor or worse? How many
>> watts would be safe to draw from these onboard connectors?
>
> The RPM signal (yellow wire) signal from the second fan might be terribly
> confusing and will cause erroneous control. But then it might not
> depending on the RPM logic... nobody nows for sure. It is best to connect
> black and red wires only to the new fan, and let the new fans rum at
> whatever RPM the partial voltage leads them to; no big deal.

The yellow (RPM) wire is not used to control the fan throttling system. The
fan speed is controlled by CPU temperature and threshold values in the BIOS.
There is a warning on fan rotation speed which can be set to 'alarm' or
'shutdown system' or 'disabled'. So getting a speed reading from just 1 fan
would be fine and shouldn't cause confusion


From: DanielEKFA on 1 Apr 2008 12:20
Hi GT and Angelo, and thanks for all your very informative replies :)

I got a bit impatient with the whole thing, I really wanted to do it, so I
just thought, well, I might as well try, worst thing I'll wreck the mobo ;)

So, I basically just did it the way I believed it to work. An indeed it does
work! Both fans are happily spinning (quite silently) and keeping the CPU
really, I mean, REALLY cool.

I hadn't thought about the fans preferably being the same type, but luckily
enough, they're exactly the same (came with my case), so probably I won't
get any weird behavior on that account.

On a side note, reading up on the connectors and wires prior to this, I
found out that the "7V trick" to slow fans down is not always so good on
one's PSU, and I had five fans connected like that in my case! So, I pulled
out those and replaced them with just one fan running at 12V. Hopefully that
will clear up some weirdness I've been having with a couple of drives.

I don't know if the two fans running on the same connector will cause them
to run slower when maxing out, but here in idle they run at the same speed
as before, when one was connected to a chassis connector. Either way, with
the temps I'm having ATM, I don't think it'll be much of an issue ;)

I don't really understand the stuff Angelo writes at the end of his message,
with the scope and all, but is it very important? Or, now that it runs
(seemingly fine) have I, without knowing it, proved the risky way that it is
switched, analog partial, or smoothed, if those are even different? :)

Sorry, not that skilled in electronics, I can handle a soldering iron and
give myself some electric shock now and then, but the theoretical stuff is
pretty much unchartered territory to me ;)

Once again, thanks for your help!

Cheers,
Daniel :)


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