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Old 04-06-2010, 07:32 AM   #1
mattch
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Default dell cpu fan wires

Anyone know whats up with dell cpu fan wires?

i have pc where cpu fan died, its 3pin red, white, black.

my replacement has 5pin (well 4 wires on 5 pin connector, red, white, blue, black)

My question is anyone know how to wire this thing up without it running full blast?

i swapped connectors on the bad cpu fan so i dont have to do any splicing, but not sure what to do with white or blue wire.

when i use white wire it runs full blast when i use blue wire it runs full blast. .
when i connect blue and white wire to last pin it slows down but still sounds like hair dryer...

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Old 04-06-2010, 07:42 AM   #2
mattch
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Default Re: dell cpu fan wires

i think i found answer, not the one i was looking for

red
black
white - rpm
blue - pmw

i guess that means since my dell mobo doesnt have that 4th pin there is no PMW so the PMW fan will run full speed..

i wonder how intel does it, seems like no problem using a 4pin cpufan on 3pin header
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Old 04-06-2010, 07:58 AM   #3
washu
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Default Re: dell cpu fan wires

A lot of Dell 3 wire fans are temp controlled. The fan itself has a sensor which changes the RPM depending on the temperature. Anything else will run full speed because the MB doesn't vary the voltage at all.

You can try using a big fan and run it at a lower voltage. Your PWM fan is not a good candidate as they don't usually work well at voltages significantly below 12.
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Old 04-06-2010, 08:56 AM   #4
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Default Re: dell cpu fan wires

Dell 3 wire fans is not RPM sensed. It's zero rpm failure detection even it will not set off even the fan is spinning at 100rpm. I have tested and confirmed this behavior. My fix for bog standard 3 wire fans in Dell is make a jumper and jump pin 1 and 3 to prevent alarms and feed 12V from center pin and jumper (it is grounded) and use a fan rpm control to keep rpm under control.

Cheers, Wizard
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Old 04-06-2010, 09:26 AM   #5
mattch
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Default Re: dell cpu fan wires

Think there is a way to trick the PWM by giving it some power?

specs:
PWM Fuction: 2.05A avg, 3.2A peak,
PWM Signal duty cycle Speed: 0-20% 1000RPM, 100% 5750RPM
Rated Voltage: DC 12V

does that mean 12v 3.2A will give me 100% rpm?
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Old 04-06-2010, 09:32 AM   #6
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Default Re: dell cpu fan wires

whoa.
i know what a fan that draws 2 amps sounds like. is that one of the big Deltas?
but no, you need a PWM (pulse width modulated) signal to control it. you can either buy a fan controller (i suppose the ones that do pwm are not cheap) or you can hack together a simple 555 circuit.
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Old 04-06-2010, 10:06 AM   #7
mattch
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Default Re: dell cpu fan wires

2.6A - DATECH

ill check into that 555 circuit, sounds neat

i read that when the PMW circuit is open it runs full duty
and when grounded it runs at 0%, so i have running at 0%, i assume is about 1000rpms? im going to monitor the temps and see how it goes.
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Old 04-06-2010, 10:24 AM   #8
Wizard
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Default Re: dell cpu fan wires

555 timer IC is *excellent* to build a PWM circuit with a potentiometer, and drive a small signal TO-92 NPN with either pull up or pull down resistor on the output for the PWM input of fan itself. Heck, you can change potentiometer for PTC sensor and tune the circuit for minimum rpm at cold temp and limit the rpm for noise at warmest temp.

Cheers, Wizard
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Old 04-06-2010, 12:58 PM   #9
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Default Re: dell cpu fan wires

You can plug a standard fan into the Dell port if you make a conversion harness by clipping the wires close to the old connector and soldering new ones to your new fan.

If you don't want to do that they do make easy plug and play conversion harnesses for these boards.

Here is the 3 pin converter one for your board this will allow a standard 3 pin fan to connect.

http://www.svc.com/25004-4.html

Here is the pinout I believe you're looking for for the 5 pin fan.

http://pinouts.ru/Motherboard/dell_fan_pinout.shtml
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Last edited by Krankshaft; 04-06-2010 at 01:02 PM..
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Old 04-06-2010, 01:33 PM   #10
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Default Re: dell cpu fan wires

Quote:
Originally Posted by Krankshaft
You can plug a standard fan into the Dell port if you make a conversion harness by clipping the wires close to the old connector and soldering new ones to your new fan.

If you don't want to do that they do make easy plug and play conversion harnesses for these boards.

Here is the 3 pin converter one for your board this will allow a standard 3 pin fan to connect.

http://www.svc.com/25004-4.html

Here is the pinout I believe you're looking for for the 5 pin fan.

http://pinouts.ru/Motherboard/dell_fan_pinout.shtml

No need for any connector rigging, both new and old fan are dells, so same connector, i could just remove wire from old one and place on new one.
Of course thats the right way, i did it the fast no patients way, i just rip off the plast connector on MB so now i can do what ever i want

I didnt know they made adaptors, good to know for certain things.

Still my main problem was the forth wire, the blue one, the pmw one, they dont make a 4pin to 3pin adaptor. Nor would such work sence the MOBO doesnt have anythign for that, i would need a controllor.

After i got the fan to slow down i got that "Alert previous Cover" crap, not sure why since i still had white wire in place for zero rpm fan detection, anyway a small wire to jump that white wire to ground fixes that annoying error.

So with blue grounded to case, white and black jumped, the new 4-pin PMW fan is doing its job well and quietly.

I ran IntelBurnTest and it passed, so for what its being used for im haappy with it.

I appreciate all the input from everyone! for you for me
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Old 04-06-2010, 04:13 PM   #11
Krankshaft
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Default Re: dell cpu fan wires

Yeah those fans don't get controlled by the PWM on the mobo I remember reading that they have a thermistor in the fan hub that regulates their speed. Also make sure that the fan blows out the back and not into the case. If it blows in flip it around.

A stupid poorly designed Dell cooling scheme that they'd defend to the grave. "Aggressive cooling system" my ass.

Sure suck in hot air from the PSU fan right above the case fan then blow it over the CPU then blow that same superheated air (from both the PSU and CPU heatsink) across all the other components and out the front.

Not to mention where does the PSU fan draw it's air from again? Exactly from INSIDE the case!

Last edited by Krankshaft; 04-06-2010 at 04:20 PM..
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Old 04-06-2010, 07:02 PM   #12
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Default Re: dell cpu fan wires

I've seen a few Dimension 4700s with the 92mm rear fan blowing in... They idled at over 60 celsius, had blown Rubycons and KZJ. The sheet metal of the case was actually warm to the touch. I recapped, flipped the fan around, and the temperatures dropped significantly.

I've also seen 4700s with the fan blowing out, which leads me to think that Dell corrected this at some point.
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Old 04-06-2010, 09:14 PM   #13
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Default Re: dell cpu fan wires

The fan was probably flipped by the user I read on their knowledge base that they recommend NOT to flip the fan and it was manufactured this way and doing so could cause overheating and damage to the VRM. Quite the opposite in fact .

I love companies who stick to their guns even if they're wrong.
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Old 04-07-2010, 09:41 AM   #14
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