I have purchased a new front fan for my case and did the 7-volts trick, using the supplied molex adapter and switching the cables around and everything works fine.
The only problem I have is that I would like to use the speed sensor (yellow wire). I have found an extra 3-pin connector from a broken fan and plugged the yellow wire in the proper position, but it doesn't get read from SpeedFan or ASUS PC Probe.
What would be the proper wiring to use, if doable at all?
In article <1146146797.904676.315200@y43g2000cwc.googlegroups.com>, "lupo666" <lupo666@libero.it> wrote:
Hi all,>
I have purchased a new front fan for my case and did the 7-volts trick,> using the supplied molex adapter and switching the cables around and> everything works fine.>
The only problem I have is that I would like to use the speed sensor> (yellow wire). I have found an extra 3-pin connector from a broken fan> and plugged the yellow wire in the proper position, but it doesn't get> read from SpeedFan or ASUS PC Probe.>
What would be the proper wiring to use, if doable at all?>
Thanks, Lupo
If you are using the 7 volt trick, I don't see a good reason why the tacho output signal would work. The tacho output is ground referenced, and when you connect the fan black and red wires to +5V and +12V respectively, the tacho is referenced to +5V, and can no longer pull to ground. That is bound to upset the monitor chip, and it will not see a signal.
If you want to drop the voltage to the fan, and have the tachometer output work also, try this:
| | | | | | | +12V ---|>|--|>|--|>|--|>|--|>|--|>|--|>|------- to fan +12V | | | | | | |
GND ------------------------------------------- to fan GND
The component in the picture, is a 1N4001 switching diode. Any of the family of diodes would work, from 1N4001 through 1N4007, and they are rated for 1 ampere of current max. Each diode will drop roughly 0.7V, (12 - 7*0.7) = 7.1 volts. I have a string of those diodes in my gaming PC, for the main fan.
You don't need solder, and you can just twist the leads of the diodes into a chain. My local electronics store sells these diodes in bags of 25 for about $3 or so. Many other sources sell them for a lot more, so shop around.
There is a band marking on one end of the diode, and in the above picture, the band is on the right hand side of each diode shown in the picture.
Make sure you insulate the leads on the diodes, so they cannot touch anything in the computer. Mounting the diodes on a piece of perfboard would be an alternative way to mount them, and the perfboard will make it easier to come up with a techique to mount the diodes inside the computer.
To make the fan run faster, use fewer diodes.
To make the fan run slower, use more diodes.
With the above diode technique, the tachometer signal will work.
You can also try running the fan from +5V and GND, which will make the fan a bit slower than it is at 7V, but again, the tachometer signal will pull to ground properly. Some fans will not start with just 5V on them, so you'll have to test it and see what happens.
I have purchased a new front fan for my case and did the 7-volts trick,>>using the supplied molex adapter and switching the cables around and>>everything works fine.>>
The only problem I have is that I would like to use the speed sensor>>(yellow wire). I have found an extra 3-pin connector from a broken fan>>and plugged the yellow wire in the proper position, but it doesn't get>>read from SpeedFan or ASUS PC Probe.>>
What would be the proper wiring to use, if doable at all?>>
Thanks, Lupo>
If you are using the 7 volt trick, I don't see a good reason> why the tacho output signal would work. The tacho output is> ground referenced, and when you connect the fan black and red> wires to +5V and +12V respectively, the tacho is referenced > to +5V, and can no longer pull to ground. That is bound to > upset the monitor chip, and it will not see a signal.>
If you want to drop the voltage to the fan, and have the> tachometer output work also, try this:>
| | | | | | |> +12V ---|>|--|>|--|>|--|>|--|>|--|>|--|>|------- to fan +12V> | | | | | | |>
GND ------------------------------------------- to fan GND
In article <vS74g.11582$Qz.9873@fed1read11>, UCLAN <nomail@thanks.org> wrote:
Paul wrote:>
I have purchased a new front fan for my case and did the 7-volts trick,> >>using the supplied molex adapter and switching the cables around and> >>everything works fine.> >>
The only problem I have is that I would like to use the speed sensor> >>(yellow wire). I have found an extra 3-pin connector from a broken fan> >>and plugged the yellow wire in the proper position, but it doesn't get> >>read from SpeedFan or ASUS PC Probe.> >>
What would be the proper wiring to use, if doable at all?> >>
Thanks, Lupo> >
If you are using the 7 volt trick, I don't see a good reason> > why the tacho output signal would work. The tacho output is> > ground referenced, and when you connect the fan black and red> > wires to +5V and +12V respectively, the tacho is referenced > > to +5V, and can no longer pull to ground. That is bound to > > upset the monitor chip, and it will not see a signal.> >
If you want to drop the voltage to the fan, and have the> > tachometer output work also, try this:> >
GND ------------------------------------------- to fan GND>
[...snip]>
Why not just use a 5.1v zener diode?
Power dissipation ? You wouldn't want to use one of those tiny 400mW ones. And a 5 watt zener is $1.20 at Digikey, and I think I can get the 1N4000 series cheaper.
Even with the diode scheme, you shouldn't really run it all the way up to an amp. A couple hundred milliamps probably won't hurt.
I was going to mention a three terminal regulator and a couple 0.22uF decoupling caps as another solution, but I don't know if those are that easy to find. And that is too much of an electronics project Next, people will want a pot on it, so they can dial the voltage.
If you are using the 7 volt trick, I don't see a good reason>>>why the tacho output signal would work. The tacho output is>>>ground referenced, and when you connect the fan black and red>>>wires to +5V and +12V respectively, the tacho is referenced >>>to +5V, and can no longer pull to ground. That is bound to >>>upset the monitor chip, and it will not see a signal.>>>
If you want to drop the voltage to the fan, and have the>>>tachometer output work also, try this:>>>
| | | | | | |>>> +12V ---|>|--|>|--|>|--|>|--|>|--|>|--|>|------- to fan +12V>>> | | | | | | |>>>
GND ------------------------------------------- to fan GND>>
[...snip]>>
Why not just use a 5.1v zener diode?>
Power dissipation ? You wouldn't want to use one of those tiny > 400mW ones. And a 5 watt zener is $1.20 at Digikey, and I think> I can get the 1N4000 series cheaper.
My time is worth a lot more than the difference in price between 8- 1N4000 series diodes and ONE $1.20 zener. The installation is not as messy, either. A chassis mount 100 ohm pot is the solution *I* use on my machine.
Hi, thanks for the replies, they were very helpful. The reason I chose the 7V trick is because is clean (just switched the molex wires around) and gives me more than 5V, which is a bit too low. I think, in the end, I'll do w/o the fan monitoring, because is not the CPU or power fan and just keep monitoring the HDs, MB and CPU temperatures for any anormalities...
As I said, my time is worth a lot more than the difference in>>price between 8 diodes and ONE 1W zener. Construction ease and>>"neatness" is also better with the zener. If I want to make it>>difficult, I'll use a 100 chassis mount pot.>
It's still a sub-optimal solution.>
Do you expect anyone to have these > 1W zeners?
Do you expect the average reader of this NG would have a stash of 1N4000 series diodes?
Did you expect a local shop to have them?
My local Radio Shack has them. And all online parts outlets, such as DigiKey and Newark, have them.
Unlikely, you'd be special-ordering them at a price premium because> very few people use them... why would they when a typical 10 cent zener> and 50 cent Darlingtion can be made into a pass-transistor arrangement> if you want more current... Then it's still much lower than it's> current rating too.
Right...and the average NG reader has *those* on hand. Uh huh...
A zener simply isn't optimal, nor are diodes. Current limiting is, and> is possible just as easily, cheaper, and with more readily available> parts when using resistor(s).
So you are in agreement with my 100 ohm chassis mount pot solution?
The value of your time is in special-ordering these zeners when it> takes far less time to find the resistors, or they're common enough> some might already have them. I keep random stock of misc. electronic> parts here, including zeners, diodes, resistors and quite a bit more.
It takes me just as long to order 1N4000 series diodes online as it does to order the correct zener. I don't care what random stock you keep. The average reader of this NG does not, and will likely end up ordering his parts. The 100 ohm pot is available at Radio Shack as well. Use high fan speed when you need it; slow it down when you don't.
The only way to reduce the current that DC computer case fans draw>>is to reduce the voltage across them. A resistor in series drops>>the voltage across the fan simply by dropping voltage itself. I>>would *really* be interested in your solution of reducing fan speed>>of a 12v fan while still giving it 12v.>
It's not my problem if you can't understand the difference.> You'd have to consider how a fan draws current, it is not a steady> current draw. Limiting with the resistor does control this better, it> is at the core of what voltage limiting vs current limiting, is,> regardless of fans.
I understand how a fan draws current just fine. Nice current pulses, usually two pulses per revolution. I designed a amplifier for these pulses that would sound an alarm if the fan stopped. Worked fine. Your resistor just drops a varying amount of voltage depending on the fan being used (different current demands.) The SAME zener can be used with most fans and still provide the same 7v to the fan.
It's pretty simple. It's unlikely most people have the >1W zener, so> (excepting you, apparently), they can't make do with parts they already> have.
It's unlikely most users have ANY parts on hand, let alone the correct value resistor for his fan. A zener doesn't care. You can use the same one on a fan that draws 100mA or on a fan that draws 200mA. Not so with a resistor. Remember, this problem was about quieting an already existing system.
Current capability is not a factor in determining if a device is a>>rheostat or a potentiometer. How the terminals of the device are>>connected in a circuit is the determining factor. A potentiometer>>with its center contact shorted to either end becomes a rheostat.>>A low current potentiometer becomes a low current rheostat. A chassis>>mounted potentiometer wired as a rheostat makes an excellent fan>>speed control.>
In practice, you're either buying a lab-grade pot at extreme expense if> it can handle the current or it's called a rheostat. Not theory here,> I mean actually going and buying the thing.
I'm talking definitions here. A three terminal variable resistor is called a potentiometer. As soon as you connect the center terminal (wiper) to one of the end terminals, it becomes a rheostat. Doesn't matter what the current or power rating is. Even a 1/4W pot can be used as a rheostat.
- I don't need to change the fan speed, it gets set right at first and>>>never fiddled with. Fine-tuning down to a dozen RPM one way or the>>>other is pretty insignificant, IMO, and might not be obtainable anyway>>>on the wire-wound types since there is an inherant granularity to the>>>adjustment when it hits each wrapping of the element wire.>>
Many people want high fan speed when it's needed, and lower fan speed>>when the computer is on, but idling. Soldering ONE pot is certainly>>easier than soldering seven or eight diodes.>
Actually they may assume it but don't really know what they need. A> properly designed chassis cooling system can handle full load WITHOUT> the fans running at high speed. IMO, it's just silly to reach down and> fiddle with a pot and have that higher noise when one can have it> quieter and never have to adjust it. You are too consumed with control> methods and not enough with fan selection.
But this thread was about quieting an EXISTING system using the EXISTING fan, not about proper design for cooling and selecting the correct fan.
I actually DO THIS stuff> constantly, it works fine to have single speed fan, no overheating even> with overclocking. Even so, if it's your box and you want a rheostat,> have fun with it even though it's not necessary for cooling or noise> reasons unless the system owner made a bad case choice and refuses to> correct that mistake instead of trying a work-around.
Re-read the above. This is about someone who asks what he can do to quiet his present fan, other than "the 7v Molex reversal" solution (which the OP did.)
Horse manure! You want a part that provides 50 years of life in a PC>>that is upgraded every few years? And your thermal issues are without>>merit. The entire case is a heatsink, though not needed in such a>>low power application. You're grasping at straws here.>
You are clueless, the entire case is not a heatsink.
If it's metal, and constructed with metal screws, it sure is. You're not using plastic cases, are you? Any heat buildup in the chassis mounted pot will be transfered to the chassis, just as the chassis gets quite warm in the area of the PSU.
Those will work, go ahead and do it. It's not necessary though, more> expensive and less reliable. Seems the only reason to do it is if> prior case or fan choices were poor or if you are just to stubborn to> accept that there is a better way.
Sigh...we're assisting someone who wants to quiet his existing fan by methods other than the connector reversal, remember?
Low speed fans are not the usual candidates for quieting, are they?>
yes, why on earth would someone who wants quiet fans, start out by> buying a higher speed fan?
[..snip]
Nice essay, but this is about ways to quiet an *existing* noisy higher speed fan, remember? The OP did the "Molex reversal" thing. We started giving him alternatives, remember?
You dont' need much better resolution in most cases, merely to be able> to hit rougly 10 Ohm near enough to the target. If what you need for> very quiet (near if not entirely silent) operation is about 125 Ohms,> then 100 Ohms just won't cut it. It is in fact very common to need> about 120 (+-10) Ohm with optimal low speed fans from many of the major> manufacturers, unless the user wasn't going for such a low speed to> begin with and if they aren't going for such a low speed, they might as> well just buy that low speed fan to begin with and it might be what> they wanted, ie- about 2200 RPM. I aim lower than 2200 RPM though,> often under 1000 RPM is possible, particularly with chassis that accept> 120mm fans.
Again, this was about quieting an existing higher RPM fan, not fan selection. But please let me know what fan you are using that draws less than 50mA. 50mA would give a 5v drop on a 100 ohm pot. Any more of a drop would put it in the unreliable startup range when it gets old and dirty.
So in conclusion, a 5W zener will work but there's no reason to use one> over other methods, the best of which being a power resistor if later> adjustment isn't necessary.
What value resistor? The OP likely didn't want to experiment with multiple resistors. The resistor needed for a 100mA fan would be quite different that with a 200mA or 300mA fan. What fan does he have? The 5.1v zener will work with all three fans.
If adjustment is necessary and you want only a low-power-rated pot, you> want that pot in the voltage divider feedback of a (usually integrated)> regulator, NOT handling the load current.
I know of no low power pots that are chassis mount.
To handle the load current> you will have to spend a lot more for the rheostat or even rarer pot,
Any run-of-the-mill chassis mount pot wired as a rheostat works fine.
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