[SOLVED] Unable to connect 2-pin fan to pc - help?

Jan 30, 2021
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First build, running into some troubles getting a fan working.

Case is a second-hand Thermaltake Armor MX. It's an old case, and as I understand the stock fans are meant to connect directly to the psu. (I got the whole thing for $15, so not complaining.) However, the side fan's connector only has two pins, and because of its size it's physically unable to slot into any molex connector on the psu.
Some pictures to demonstrate what I mean:


I'm not really sure how to get it running. I've tried connecting it into the motherboard fan header, both ways, ground to the first pin, nothing. I think I may need some kind of adapter to get it to plug into molex - would this be right? I've tried searching a bit and I haven't found anything of the sort that's sold here in New Zealand, not sure if I'm using the wrong terms or what.

I will mention that the other case fan's connectors are different:


I've been considering the idea of getting a molex cable like this, cutting the connector off the other fan and jury-rigging it into there. I'm not experienced with these things though and obviously I don't want to go around cutting up fans without knowing what I'm doing.

tl;dr no clue how to plug it in, would appreciate any ideas.
 
Last edited:

Paperdoc

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Yeah, I don't know of any off-the-shelf adapter.So you'll have to rig it yourself by cutting and soldering. The keys here are Voltage rating and polarity of the fan. Check the fan for markings - almost all fans now are designed for use on a power supply of 12 VDC, but since this one is not a current "standard" fan, look for that spec just in case it is not designed that way. On polarity, we can't see in your photo, but the standard coding is Black for Ground (-), and Red for +12 VDC. You should note in your last photo of another fan plugged into a 4-pin Molex PSU output that the colour codes do NOT match exactly. Black goes to Black (Ground), But fan RED goes to Molex YELLOW for the +12 VDC line.

You really have two alternatives available. You can splice into lines from a PSU Molex output to get a constant 12 VDC supply so the fan runs full speed all the time. But you could arrange to connect to a mobo fan header IF it is configured properly and get the fan under automatic speed control. Your old fan will operate just like the older type of standard fan called a Voltage Controlled fan, or 3-pin fan. Its speed is controlled by a mobo header simply by varying the voltage supplied to it, which a PSU cannot do. Your fan does not have the third wire of standard 3-pin fans, but that is only to send back to the header the fan's speed signal. That signal is NOT required to operate the fan, so the only impact MIGHT be that the header sends you an error message that the fan has failed because the header did not get a speed signal). To do this you could splice onto wires from another fan already plgged into a header, or get an old junk 3-pin fan and cut off its wires (with connector) and splice two of them onto your fan's wires. The standard fan's wires will be Black and Yellow as above for a 3-pin fan (NOT the same colours used on 4-pin fans), plus a YELLOW wire from Pin #3 you will NOT use.

To be sure of polarity, don't rely on wire colours completely. Instead I'll detail pin identification on the header. Mobo fan headers now are usually 4-pin always, although you may find some on older boards with 3 pins. In BIOS Setup on most boards you have a configuration option for each header to set its MODE of operation - that is, which type of signals it outputs to its fan. For new 4-pin fans this is to be set to PWM Mode. For older 3-pin fans such as yours, set it to Voltage Control Mode or DC Mode. Now, look at the actual header. It will have three (or four) pins sticking up, and a plastic tongue next to Pins 1 to 3. IF this is a 4-pin header, Pin #4 is beyond the tongue. Arrange so the pins are closer to you, and the tongue behind them. Then Pin #1 (Ground, black wire) is on your RIGHT, and Pin #2 (+12 VDC, Red) is in the MIDDLE of the tongue. So you can make custom connections from those two pins to your fan's 2 wires. When you connect that way, and configure the header to use DC Mode, the mobo will be able to control the fan speed just like any more modern fan.
 

Paperdoc

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Ambassador
Yeah, I don't know of any off-the-shelf adapter.So you'll have to rig it yourself by cutting and soldering. The keys here are Voltage rating and polarity of the fan. Check the fan for markings - almost all fans now are designed for use on a power supply of 12 VDC, but since this one is not a current "standard" fan, look for that spec just in case it is not designed that way. On polarity, we can't see in your photo, but the standard coding is Black for Ground (-), and Red for +12 VDC. You should note in your last photo of another fan plugged into a 4-pin Molex PSU output that the colour codes do NOT match exactly. Black goes to Black (Ground), But fan RED goes to Molex YELLOW for the +12 VDC line.

You really have two alternatives available. You can splice into lines from a PSU Molex output to get a constant 12 VDC supply so the fan runs full speed all the time. But you could arrange to connect to a mobo fan header IF it is configured properly and get the fan under automatic speed control. Your old fan will operate just like the older type of standard fan called a Voltage Controlled fan, or 3-pin fan. Its speed is controlled by a mobo header simply by varying the voltage supplied to it, which a PSU cannot do. Your fan does not have the third wire of standard 3-pin fans, but that is only to send back to the header the fan's speed signal. That signal is NOT required to operate the fan, so the only impact MIGHT be that the header sends you an error message that the fan has failed because the header did not get a speed signal). To do this you could splice onto wires from another fan already plgged into a header, or get an old junk 3-pin fan and cut off its wires (with connector) and splice two of them onto your fan's wires. The standard fan's wires will be Black and Yellow as above for a 3-pin fan (NOT the same colours used on 4-pin fans), plus a YELLOW wire from Pin #3 you will NOT use.

To be sure of polarity, don't rely on wire colours completely. Instead I'll detail pin identification on the header. Mobo fan headers now are usually 4-pin always, although you may find some on older boards with 3 pins. In BIOS Setup on most boards you have a configuration option for each header to set its MODE of operation - that is, which type of signals it outputs to its fan. For new 4-pin fans this is to be set to PWM Mode. For older 3-pin fans such as yours, set it to Voltage Control Mode or DC Mode. Now, look at the actual header. It will have three (or four) pins sticking up, and a plastic tongue next to Pins 1 to 3. IF this is a 4-pin header, Pin #4 is beyond the tongue. Arrange so the pins are closer to you, and the tongue behind them. Then Pin #1 (Ground, black wire) is on your RIGHT, and Pin #2 (+12 VDC, Red) is in the MIDDLE of the tongue. So you can make custom connections from those two pins to your fan's 2 wires. When you connect that way, and configure the header to use DC Mode, the mobo will be able to control the fan speed just like any more modern fan.
 

Krotow

Commendable
Oct 2, 2019
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Indeed if you want to use existing case fan, get some Molex 4-pin to (anything) adapter or old cable with Molex 4-pin male connector. Then strip fan cable and Molex adapter connectors and solder fan cable wires to Molex 4-pin connector - black to black (ground) and other to yellow (+12V). Like in last picture above.

I would prefer stock fan replacing to different and quieter fan with PWM speed regulation compatible with motherboard SYS_FAN connector. Though with further TomsHardware forum reading I'm starting to think about NZ as developing country. No offence, it is sad.
 
Jan 30, 2021
14
1
15
0
Yeah, I don't know of any off-the-shelf adapter.So you'll have to rig it yourself by cutting and soldering. The keys here are Voltage rating and polarity of the fan. Check the fan for markings - almost all fans now are designed for use on a power supply of 12 VDC, but since this one is not a current "standard" fan, look for that spec just in case it is not designed that way. On polarity, we can't see in your photo, but the standard coding is Black for Ground (-), and Red for +12 VDC. You should note in your last photo of another fan plugged into a 4-pin Molex PSU output that the colour codes do NOT match exactly. Black goes to Black (Ground), But fan RED goes to Molex YELLOW for the +12 VDC line.

You really have two alternatives available. You can splice into lines from a PSU Molex output to get a constant 12 VDC supply so the fan runs full speed all the time. But you could arrange to connect to a mobo fan header IF it is configured properly and get the fan under automatic speed control. Your old fan will operate just like the older type of standard fan called a Voltage Controlled fan, or 3-pin fan. Its speed is controlled by a mobo header simply by varying the voltage supplied to it, which a PSU cannot do. Your fan does not have the third wire of standard 3-pin fans, but that is only to send back to the header the fan's speed signal. That signal is NOT required to operate the fan, so the only impact MIGHT be that the header sends you an error message that the fan has failed because the header did not get a speed signal). To do this you could splice onto wires from another fan already plgged into a header, or get an old junk 3-pin fan and cut off its wires (with connector) and splice two of them onto your fan's wires. The standard fan's wires will be Black and Yellow as above for a 3-pin fan (NOT the same colours used on 4-pin fans), plus a YELLOW wire from Pin #3 you will NOT use.

To be sure of polarity, don't rely on wire colours completely. Instead I'll detail pin identification on the header. Mobo fan headers now are usually 4-pin always, although you may find some on older boards with 3 pins. In BIOS Setup on most boards you have a configuration option for each header to set its MODE of operation - that is, which type of signals it outputs to its fan. For new 4-pin fans this is to be set to PWM Mode. For older 3-pin fans such as yours, set it to Voltage Control Mode or DC Mode. Now, look at the actual header. It will have three (or four) pins sticking up, and a plastic tongue next to Pins 1 to 3. IF this is a 4-pin header, Pin #4 is beyond the tongue. Arrange so the pins are closer to you, and the tongue behind them. Then Pin #1 (Ground, black wire) is on your RIGHT, and Pin #2 (+12 VDC, Red) is in the MIDDLE of the tongue. So you can make custom connections from those two pins to your fan's 2 wires. When you connect that way, and configure the header to use DC Mode, the mobo will be able to control the fan speed just like any more modern fan.
Thanks for the super detailed post, I'll muck around and see what I can do.
 
Jan 30, 2021
14
1
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Update: So I tried plugging the fan into the mobo header again. I was careful to connect the pins to the right headers and set it to 3-pin mode in the BIOS. Again, nothing worked, but when I turned the PC off to inspect it further I noticed a burning plastic smell coming from the direction of the fan header. I was able to boot into it again fine but after restarting I got a black screen.

I've done some troubleshooting. This particular gpu (Asus GTX 970) will no longer output any kind of image to the monitor - no BIOS, no OS, nothing. I've tried clearing the CMOS to no avail. A much older gpu (GTS 250) works more or less - I'm able to see the BIOS and boot into Windows 10, but I get a black screen when booting into Ubuntu. I thought this might be because I still have the drivers for the 970 installed, but I'm unable to boot into Ubuntu on a usb without going into safe graphics mode. I also got an error message and no bootup before changing the port my usb was plugged into.

Unfortunately I don't have access to a 2nd pc to test the gtx 970. The fan is rated for 12V and 0.38 amps (it's 230mm wide). As I understand this is fine for a fan header. Is it really safe to connect molex fans to the motherboard, or is there a chance my motherboard is faulty? Gigabyte B450M S2H V2.

Any advice would be appreciated, at this point I'm stuck again. I can move this to a different thread if it's getting too off-topic.
 
Last edited:

Paperdoc

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A 4-pin Molex power outptut female connector from the PSU contains lines for Ground, +12 VDC, and +5 VDC. So normally you would connect anything to use either 12V or 5 V power. Some people use a connection betwwen the +12 V and the +5 V lines to get an effecive 7 VDC power supply. But those are the only choices.

IF your odd fan was designed for 12 VDC power, and IF you connected with the correct polarity to the correct pins of the mobo header, it certainly should work. If the fan were designed for 5V or 7V operation (very unlikely) and were connected to the 12 VDC line and Ground, the fan should have started VERY fast and maybe burned out in a short time. What you report is NO result at all.

So two possibilities come to mind. One: you were wrong to assume it was intended to connect to a Molex output in some way. Or, two: the fan is faulty. You can do a simple check of the fan even if you don't have another computer and mobo header to use, in either of these ways (be careful - the fan might start up!)
(a) Make temporary connections to the fan from an unused Molex output from the PSU, noting that the Molex BLACK is Ground, and YELLOW is +12 VDC.
(b) Use an automobile 12 VDC battery as your power source with temporary wires. On an auto battery, the LARGER diameter post is +, the smaller is -.

If those show that the fan works well given 12 VDC power, then there's a problem with your mobo header OR with the way you connected it. But if the fan will not run when given those alternative power sources, you know the trouble is in the fan.

I'm not clear how trying to get an odd fan connected suddenly became an attempt to diagnose a video card.
 
Reactions: Krotow
Jan 30, 2021
14
1
15
0
Alright, thanks for the info. I'll try another method when I have the time.

I brought the GPU up as it failed shortly after trying out the fan and I'm somewhat worried the motherboard is damaged or something - the burning plastic smell is worrying. That being said it could be coincidental, or I could have the wrong idea. I'll make a new thread regarding that issue.
 

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