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How to get the most combined power with two molex connections?

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April 2, 2012 11:45:32 AM

My fan controller (Sentry Mix from NZXT) requires two molex connections in order to supply 50 watts to each fan, would my fans run faster if the two molex connections came from separate cables on the psu or would it be fine of they both drew power from the same output on the psu (its a modular psu), because i have cables that have 4 molex connections on them. So, i guess my question is, does more power go through one connection each on two psu outputs, or on two connections on one cable? What is the best way to power the fan controller? Thanks
a b ) Power supply
April 2, 2012 12:10:57 PM

two molex from a psu will do fine
its about how many amps each rail is pushing
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a c 243 ) Power supply
April 2, 2012 12:12:21 PM

I'd just like to know where you're getting fans that require 50 watts of power :o 
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April 2, 2012 1:07:42 PM

Power=I^2*R=V^2/R=VI. Voltages do not add up in parallel only in series and currents don't add up in series just parallel so you can do the math yourself cause Im not sure about your question.

2amps at 12volts = 24 watts
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a b ) Power supply
April 2, 2012 1:35:19 PM

Hi


I went looking to see what the power rating of a typical 140mm fan was

http://www.quietpc.com/products/120mmfans/ae-shark-140-...

say 4 or 5 watts which requires less than 0.5Amp
V x A = W

5 /12 Amp

This is insignificant for a molex connector

see http://en.wikipedia.org/wiki/Molex_connector

Fan speed depends on Voltage max speed with 12V
voltage on speed regulated fan may drop to 6V or 7V at low setting

50 watts would drive a large collection of giant case fans

If you have a cable with nothing else on it but the fan controller the molex connector would be able to deliver its maximum rated current without any voltage drop

regards

Mike Barnes


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April 2, 2012 1:58:27 PM

According to wikipedia, tipical molex connectors use AWG18, which are rated to 18A. So at 12V means 216W. So I would say you can safely take the connectors from the same cable unless you use a high-power device on that cable. In that case, check if you PSU really has 2 or more rails (I suppose if you NEED 50W/channel at 12V, they you have a 1000+W PSU with 3-4 SLI/crossfire configuration).

But the way you put the question, it bothers me a bit: will you be using a (couple of) standard 10$ fans (dont quote me on prices...I just put a small number)? Let me try to explain:
1. the Sentry will output 12V (depending on your sliders) and give to the fan up to 50W (those are the specs).
2. The fan will try to spin at an rpm related to voltage. That is what you control with the sliders.
3. If the fan encounters physical resistance, it will try to keep the same rpm, but increase the current (and power).
4. If the current reaches the max. designed value, the fan rpm will drop.

So what I say is that you cannot feed a low-power fan with higher power. You can try to force it, but only by giving it a higher voltage (so impossible with your Sentry), but it could overheat and fail.

PS: just for reference: the Antec Skeleton's 250mm top fan is rated at max 5W@12V. Since this is the biggest fan I can find now, I doubt you will encounter 10W fans, let alone 50W.
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April 3, 2012 12:21:37 PM

mathew7 said:
According to wikipedia, tipical molex connectors use AWG18, which are rated to 18A. So at 12V means 216W. So I would say you can safely take the connectors from the same cable unless you use a high-power device on that cable. In that case, check if you PSU really has 2 or more rails (I suppose if you NEED 50W/channel at 12V, they you have a 1000+W PSU with 3-4 SLI/crossfire configuration).

But the way you put the question, it bothers me a bit: will you be using a (couple of) standard 10$ fans (dont quote me on prices...I just put a small number)? Let me try to explain:
1. the Sentry will output 12V (depending on your sliders) and give to the fan up to 50W (those are the specs).
2. The fan will try to spin at an rpm related to voltage. That is what you control with the sliders.
3. If the fan encounters physical resistance, it will try to keep the same rpm, but increase the current (and power).
4. If the current reaches the max. designed value, the fan rpm will drop.

So what I say is that you cannot feed a low-power fan with higher power. You can try to force it, but only by giving it a higher voltage (so impossible with your Sentry), but it could overheat and fail.

PS: just for reference: the Antec Skeleton's 250mm top fan is rated at max 5W@12V. Since this is the biggest fan I can find now, I doubt you will encounter 10W fans, let alone 50W.


Thanks, that makes sense, one last question though, should I still get this fan controller? If I were to supply the 50 watts to the fans wold they break? I just dont want to get this and then have to be careful supplying too much power to the fans
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April 3, 2012 12:35:55 PM

gecko97 said:
Thanks, that makes sense, one last question though, should I still get this fan controller? If I were to supply the 50 watts to the fans wold they break? I just dont want to get this and then have to be careful supplying too much power to the fans

Your fans will be fine. The wattage going to the fans is related to v=Ir with current being i and r being resistance. Your internal resistance of your fan is essentially constant. Therefore when you supply a certain voltage your current goes up which means that you can not supply more wattage then what the fan is rated for because you cannot increase the voltage past 12v. Your fine.
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Best solution

a b ) Power supply
April 3, 2012 1:36:47 PM

@gecko97

Simple Explanation for you, a fan controller is load rated at 50w means it can handle a total fan load of 50w, it does not deliver 50w it allows 50w to flow through it, meaning if the amount of fans you'll be running all together total 60w, then that's too much load for the controller to handle.

If the total fan load is 10w then the fan controller will not be overloaded because the total fan load will be drawing the 10w the fans need to run, and that's all the fans can draw, the fan controller itself does not force 50w into the fans, it does not work like that.

But it will limit the load by use of a variable resistor for each fan, the individual fan control allows full voltage flow or limits the voltage flow the fan can draw and that's how the fan speed is controlled, by limiting or not limiting the voltage going to the fan.

If the fan controller requires 2 molex power supply connections it is probably a safety design splitting the controller into 2 circuits, sharing the load, one molex power supply branch will be just fine to power it.

After further investigation to satisfy my own curiosity regarding your NZXT Sentry Mix Fan Controller.

That's a serious load handling fan controller you have, it has 6 50w individual slide controllers more understandable why it has 2 molex power supply connections, I'm not really sure why NZXT felt the need for such a power load rating 6 50w 120mm fans could probably make your PC hover in the air, and the noise level would be so bad you'd have to be in another room at the other end of your home with wireless keyboard and mouse.

I'm making that statement jokingly I'm sure somewhere on this planet there exists a 12v 50w cooling fan, hidden away and isolated in some hidden room somewhere away from human beings, with ears to hear with.

When I did the Cooling Fan roundup 2012 some fans were eliminated for being too loud to be test candidates and I still have 2 of those fans 12v 120mm x 25mm 20w each pulling 1.68A at 5100rpm rated 58dba, I ran 2 of those at one time and had to leave the testing area.

If those were only 20w what would 50w fans actually be like, as far as your controller is concerned you won't have any problems running the fans you can acquire.
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April 3, 2012 8:58:14 PM

Best answer selected by gecko97.
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