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4pin case fan to 3pin controller

Last response: in Components
October 22, 2012 11:08:10 PM

OK all, I've been looking for an hour and can't find exactly this question answered, so here goes.

I have this
NZXT Sentry Mesh

I just ordered some of these

Without realizing at the time in my haste (because I'm an idiot) that they're 4-pin.

Of course my noob question is, "will this work?" Now I know the answer is no since pwm fans cannot be controlled through changing the voltage, but I'm still asking for this reason... The product description says 4 pin, but it does NOT say 4 pin PWM... are ALL 4 pin fans PWM?

And that friends, is the facepalm question of the day...

If not, I'm guessing I can just get a 3 pin to 4 pin adapter, however, I can't think of a single reason to have the 4th pin unless it's a PWM (since that's sort of the point of having that 4th pin, at least when I look at this so I'm assuming it is and I can't use a 3 pin controller.

Again, this is for my case fans ONLY, not my cpu fan.

Thanks all,
October 23, 2012 5:41:10 AM

You could buy a 3-4 pin adapter. This isn't something you really think about when choosing parts. You can find some of these on newegg or something. Shame its now backwards because my case fans are 3 pin but my mobo is all 4pins.
I would just check around online for a work-around. although i don't think the controllers would work (unless mounted on case?) Don't hold me to this, just my thoughts on it, i would call your local computer shop. or even call NCIX's toll free number they are very helpful and know what they are talking about.

haha, good luck

Best solution

a b ) Power supply
October 23, 2012 5:37:24 PM

Yes, it will work - sort of. The "sort of" is about the lights.

A 4-pin fan has 4 connections: Ground, +12 VDC (constant), fan speed pulse signal output, and PWM signal input. When it operates in 4-pin mode as designed, it uses the PWM signal with a small controller chip inside the fan motor to regulate the flow of current from the +12 VDC supply to the motor.

4- and 3-pin fan systems were designed from backwards compatibility two ways, and that's why it can work for the fan part of the operation. First, the (female) 4-pin fan connector on the end of the wires that plugs into the pins of a mobo fan port will also fit onto a 3-pin standard mobo fan port. They only plug in one way - there's a finger and groove system to limit how they fit together. When you plug a 4-pin female connector onto a 3-pin male port, you just end up with no connection for the 4th pin that carries the PWM signal. So the 4-pin fan receives only the Ground and +12 VDC signals, and also can send its fan pulse speed signal back on the 3rd pin.

Now, if you did this on a mobo 3-pin fan port, the fan would not receive a PWM signal to control its speed. However, the design is such that the PWM signal is used as an inhibitor - it slows down a fan by limiting the current drawn from the +12 VDC supply line. When connected to a 3-pin port, though, that supply line is NOT always +12 VDC. 3-pin fan port operation achieves fan speed control by reducing the voltage on that supply line. Thus the 4-pin fan receives a varying DC voltage supply and makes NO effort to modify that with a PWM signal it does not receive - it just changes speed according to its voltage supply, exactly as a 3-pin fan would do. This is the second part of backwards compatibility. In your case, the 3-pin supply port is not on the mobo, it's on your fan controller module, and exactly the same performance will result. So your fans will work just fine!

Now, what about my "sort of" comment. It appears that the LED lights in the fan are powered by the DC supply line to the fan. By design that was supposed to be +12 VDC at all times, and the circuitry in the fan taps into that supply for the LED function. However, in your case you will be connecting it to a +VDC supply that is not always 12 VDC, so when the fan speed is reduced by your controller, the LEDs will also get reduced supply voltage and go dim, or maybe even turn off. I suspect that is OK by you. If you really need those LEDs to work properly all the time, you might have to investigate how to alter the fan wiring to supply a reliable +12 VDC to the LEDs, separately from the variable +VDC supply to the fan motor.
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October 23, 2012 9:34:49 PM

Best answer selected by slimgenre.
October 23, 2012 9:34:51 PM

I was actually reading some stuff on about how someone routed the led wires on all his fans to a toggle, so I kind of like the idea of them dimming, or turning off when I don't have the fans blasting. I should have them in the mail tomorrow so hopefully get it all together in the next few days and see if that's the case. Will post update as to how it all works out.

To lengthen this discussion (just as a means of my personal knowledge) ...

If the led's dim or turn off when voltage is decreased on a 4 pin fan when using a fan controller like mine, does the same occur on a 3 pin fan or are they wired differently so you can regulate fan voltage but maintain led voltage?

Thanks again for the help :) 
a b ) Power supply
October 26, 2012 5:38:26 PM

I expect that most 3-pin fans with LEDs also will do the same thing. That is because most are not wired with separate leads for the fan motor and LEDs. A standard 3-pin fan connector has no place for a fourth wire to connect to a guaranteed-always 12 VDC supply line, so the LEDs normally are just tapped off the line to the motor, which will be reduced by any fan speed controller system.