Question Newbie PC build anxieties 01 (PC case - fans - PSU)

Nov 18, 2020
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Hello
Starting a PC build process, from A to ... I hope Z, but still afraid to replace a light bulb in the hall, I wish I can use this thread to expose and ask help for resolving the issues that will surely pop up.
I hope this can help other PC builders.
For now I got a PC case with 3 fans and a PSU and waiting for better days to buy more.
But I can't help trying to learn by experimenting so .... can somebody tell me if this is going to work without smoke ?
(just want the fan to rotate, no rgb for now)

 
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Paperdoc

Glorious
Ambassador
Yes, that will work to make the fan run at its full speed constantly and safely. Just keep fingers etc away from the blades! Well, maybe it won't work. The issue is: does the PSU actually put out power when it is NOT connected to a mobo that asks for it? I think the answer is no, unless you trick it into turning on by shorting out just the right pair of contacts. I recommend you do not do that, just in case you get the wrong contacts.

There is another way you can power the fan. It is designed for a supply of 12 VDC to run full speed. One of the easiest ways to access that power is from a car battery, which is a 12 VDC system. (Actually, it will supply just a bit more.)

Looking at your photo, look closely at the Y-adapter with two 4-pin Molex connectors (one male, one female) and one 3-pin fan male with only two pins. It can supply the +12 VDC and Ground connections from a PSU to your fan. Carefully trace the two wires from that adapter to the fan connector. The wire that goes the the fan's MIDDLE hole is for the +12 VDC line to the fan; the line on one end is the Ground line. The third wire to the fan from the missing pin is the fan's speed signal to be sent back to the mobo header, and you do NOT use that for your current purpose. Now, on the car battery the LARGER diameter post is the + 12 VDC source; the smaller post is the - Source to be used as Ground here. That smaller - post normally is connected directly to the car chassis if the battery is in the car.

So you need to connect from the two batteery posts to the two wires to the fan with the correct polarity. If it is easier, use that Molex adapter to make your connections, being sure to trace back from the fan connector to the Molex connector. At the Molex, the Ground (-) connection will be either of its two middle pins. The +12 VDC contact will be ONE of the two ends of the Molex.
 
Reactions: JaHe
Nov 18, 2020
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Thank you very much for your detailed answer.
Actually I've read that the PSU perif plug can be used when there are more fans than available plugs on the mobo.
Also I see that my fan safety current is 0.3 Ah meanwhile a car battery delivers 48 Ah so I wouldn't want the fan flying like a drone all over the house, see what I mean ? Or is that not relevant ?
 

Paperdoc

Glorious
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You are correct, you can power fans from the Perif outlet of a PSU. The issue is speed control. That source of power can supply a fixed 12 VDC to the fan, but NO means of controlling fan speed, so the fans always run full speed. It also cannot forward the fan's speed signal to the mobo, so you never can "see" the fan speed (which won't change anyway) nor can the system monitor it for fan failure - but you can do that because it's either running full or stalled. The great advantage to connecting a fan to a mobo header is that the mobo can be used (it is pre-set to do this by default) to control the fan's speed according to the actual cooling needs of your system, as measured by temperature sensors inside the CPU chip and on the mobo.

The way a fan motor like this works is, the CURRENT flowing though it is determined by the motor's fixed characteristics and the VOLTAGE supplied to it. These fans are designed to accept up to 12 VDC input. They limit the current they draw. So the VOLTAGE available from a mobo header or from a car battery is already limited to no more than 12 VDC. And the AMPS available from each of those sources is the MAX it can supply IF the load connected allows that much. To "push" even more current through a load would require that the source boost the VOLTAGE, and that cannot happen. So the actual current max is as stated: no more than 0.3 A current when the supply is the max of 12 VDC, and even that is an upper safety limit under unusual circumstances; normally the current is less than 0.3 A even with a full 12 VDC supplied.

By the way, the Amp-Hour rating (Ah) is not the right spec. That is a spec for a battery to indicate how heavy an amp current it can continue to supply for how many HOURS of continuous use before its output drops too low. This is important for use in a car that might involve extended use of the battery without re-charging, but it is irrelevant for your use here. And the max CURRENT rating for the fan is in Amps (A), not Ah.
 
Reactions: JaHe
Nov 18, 2020
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The issue is: does the PSU actually put out power when it is NOT connected to a mobo that asks for it? I think the answer is no,
Well the fan did not start after connecting to the PSU so it looks you are right.
Eventually I will connect the car battery to the Y-adapter/molex following your description or maybe a 8 x 1.5v AA Battery Holder Case ....
I see more clearly now the relation between volts and Amp and Ah ...thanks
How would the fan react to a 5V or 9V connection ? these batteries look more easy to find ...
Apparently, for connecting my 3 fans to the mobo, I will need to buy a splitter with 3 x (3 pins male headers) on one side and 1 molex on the other side to insert in one fan spot on the mobo.
But in that case wouldn't the 3 speed informations from 3 fans passing through only one end line be potentially conflicting ?
So wouldn't it be better to use one mobo spot for each fan ?
Anyway I don't understand why coolmaster provides in it's case box a splitter with 3 x (2 pins male headers) on one side and 1x (2 pins female header) on the other side while attaching a 3 pins female header to the each fan....
 

Paperdoc

Glorious
Ambassador
We'll deal in order.

1. If you connect that fan to a lower voltage source, it WILL work but at lower speed IF that voltage is high enough. For your 12V fan, a 9V supply is certainly enough and that will work. (It might drain the 9V battery, though, because those little batteries are made for small loads.) The 5 V battery might not work, though. Every fan motor has a MINIMUM voltage needed to actually start it up from stalled, and it happens that many computer 12 V fans cannot be started with as little as 5 V.

2. If you have three mobo SYS_FAN or CHA_FAN headers to use for your three fans, then certainly go ahead and simply use one fan per header. Just remember that there are two rather different groups of mobo headers and fan uses. ONE fan (sometimes more) is used to cool the CPU chip, and it always should be connected to the CPU_FAN header. That header is always guided in its automatic speed control by a temperature sensor inside the CPU chip itself. In addition, that header gives extra attention to monitoring its fan for possible failure and will take quick action if it suddenly finds its fan is not working. All of the CASE ventilation fans, however, should be connected to SYS_FAN or CHA_FAN headers. These normally are guided by a different temp sensor on the mobo, BUT some mobos give you the option to use another sensor, and a few even arrive set to use the internal CPU temp sensor, which is wrong.

3. If you opt to use a Splitter to connect two or more fans to a single header, it should not involve a Molex connector like the ones on that three-headed item in your photo. A fan Splitter has two (or more) male output "arms" (with pins) for your fans, and only one "arm" ending in a very similar female fan connector with three holes that plugs into the mobo header. A Splitter is a simple device that just connects all its fans in parallel to the header, and draws all the power for its fans from that header. The header has a limit (usually 1.0 A) for the max current it can supply to ALL fans connected to it, so this limit is a factor when using a Splitter. By far MOST modern computer fans use at max 0.10 to 0.25 A at max, so three fans is almost always OK. HOWEVER, there is a lot of confusion because there is another type of device called a HUB that can be used to connect several fans to one header. Unfortunately, sellers tend to misuse the labels Splitter and Hub as if they were interchangeable, and they actually are different. A HUB has one extra "arm" that must plug into a power output from the PSU (either a 4-pin Molex or a SATA connector), and the Hub gets all power for its fans from the PSU, thus avoiding the current limit of the host fan header. BUT that type of device can NOT control the speed of 3-pin fans, which is what you have. So do NOT get a fan Hub; stick with a Splitter if you connect more than one fan to a header. You may find a 3-pin Splitter hard to find, but any 4-pin Splitter also will work just as well.

4. You have spotted an important thing to know. Any mobo fan header processes the speed signal sent back to it (it is a series of pulses - 2 per revolution - sent to the header) by counting the pulses. As you anticipate, that only works if the header receives just ONE train of pulses - it cannot deal with two or more speed pulse trains from several fans. So any Splitter or Hub will send back to its host header only ONE fan's speed signal. Since the signal is sent on Pin #3, the simple means for this is that, among the output male connectors of the Splitter, only one has a Pin #3 to make the connection, and the other output(s) are missing that pin. Those "others" look exactly like the one in the middle of your photo. (The one in the photo is missing that pin for a different reason - the device is to connect for power from the PSU, and there is NO reason to send a fan speed signal back to the PSU that has NO way to accept and process it.)

I'll add a further note, since your fans are of the 3-pin design. That is the older type in which the fan motor speed is controlled by varying the VOLTAGE supplied to it on Pin #2. The newer fan design now is called PWM, and uses a very similar connector with a fourth pin or hole. The two types have been designed for some ability to tolerate mis-matching, with the result that you can plug either fan type into any 3- or 4-pin mobo header and it will work - sort of. The one mis-match that needs a bit of attention affects you because you have 3-pin fans. If you plug that into a 4-pin header that is using the new PWM Mode for controlling its fan, your 3-pin fan will always run full speed. BUT almost all mobos now use 4-pin headers AND allow you, in the BIOS Setup screens for configuring the individual fan headers, an option to set the header to use Voltage Control Mode (aka DC Mode) instead of the new PWM Mode. This WILL control the speed of your 3-pin fan. So, when you get things assembled, you can look for that BIOS Setup option and make the adjustment.
 
Reactions: JaHe
Nov 18, 2020
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Trying starting to summarize what you explained ....

Config 1
Using provided splitter
There is no PIN#3 so it's supposed to connect to the PSU
There is no speed control so better leave this for additionnal fans ....

Config 2
Same splitter but now the header (A) in the photo is inside one Mobo SYS-FAN
The SYS_FAN is "guided by a temp sensor on the mobo"
Does it mean that even in this 2 pins configuration the SYS_FAN can pulse to the 3 fans an increasing voltage depending on the mobo temp ?
Or is it limited to starting the fan only when the mobo temp increases ?
Or is (in whatever 3 pins configuration) PIN#3 dedicated to imposing speed to the fans, by varying voltage or by other means ?
Or is PIN#3 only dedicated to watching and reporting individually the fans speed ?
 

Paperdoc

Glorious
Ambassador
Do via Config2 if you want your fans to have their speed controlled by the mobo. Ensure that the header you use is configured for Voltage Control Mode (aka DC Mode).

The mobo header does NOT need to know the fan speed for any of its speed control function. Some people want to know what it is, so display is good for them. The header does use the speed signal for detecting FAILURE of the fan (no speed signal), but when you use a Splitter that can only return the speed of ONE of its fans, the failure detection cannot be done for the "other two", anyway. YOU still need to check from time to time that they all are working. Now, if you do use that 2-wire Splitter your mobo fan header MAY report a fan failure to your screen. If so, look in the configuration options for that header and see if it allows you to ignore the speed signal.

The automatic fan speed control is based on the temperature measured at a sensor on the mobo, and on a temp target pre-set in the header configuration options. For a 3-pin fan, the header simply adjusts the VOLTAGE sent out to the fan(s) (via Pin #2) to adjust its (their) speed for the temp observed. It does NOT try to set a speed. It tries to achieve a temperature by changing the cooling it controls. Normally it will NOT allow the fan(s) to stall; instead it will run them at a minimum speed (to avoid stalling) until the measured temp rises enough to call for more cooling, then speeds up.

In the options for the header, you can choose a control strategy or Profile. By default it will use its pre-programmed setting of what speed to run for what measured temperature. Usually also you have three other options: Turbo (or similar) which is full speed all the time, Quiet which is a fixed slow speed all the time, and Custom or Manual. That latter allows YOU to set about four points along a "curve" of what speed the fan(s) should run for certain temperatures. The best starting point is the Normal or Standard pre-programmed "curve".

IF you want to have the speed of one of your fans detected and displayed in BIOS Setup (and some other utilities), you can buy a Splitter with three or more outputs. It does not matter whether the Splitter is for a 3-pin or 4-pin fan system. But the header does not need that (as above), so it's really just your preference.
 
Reactions: JaHe
Nov 18, 2020
11
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Thank you so much for spending your time in such detailed answers and valuable feedback.
I feel more confident to keep connecting things all around.
(y)(y)(y)(y)(y)
 

arif1752002m4a1

Respectable
May 16, 2018
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Hello
Starting a PC build process, from A to ... I hope Z, but still afraid to replace a light bulb in the hall, I wish I can use this thread to expose and ask help for resolving the issues that will surely pop up.
I hope this can help other PC builders.
For now I got a PC case with 3 fans and a PSU and waiting for better days to buy more.
But I can't help trying to learn by experimenting so .... can somebody tell me if this is going to work without smoke ?
(just want the fan to rotate, no rgb for now)

Bro.. Smoke, Spark, Electric shock, is nearly impossible if you are using good PSU (as you have already)... Even you Connector everything in wrong connection, polarity.or anything.. nothing gonna explode, or you will not see any sparks.. because PSUs Already have good protection features built in.. and all these branded PSUs pass safety test before they can be used.. so you don't need to think any disaster like this..

Rest of all building a PC is as easy as solving puzzles... Everything is already well labelled.. you just need to plug things in right places.. for better guidance.. you can watch Youtube videos
 

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