Modding a Thermistor controlled case fan to add wire to sensor?

Hello all,
To make a front case fan with thermistor sensor on the end of wire for a Dell Precision 670 Workstation to use for CAD / 3D Printing -
modding a 12V case fan that has a thermistor attached :
- plan on un-soldering the thermistor :
& adding a AWG 22 twisted pair wire to put the thermistor at the end so that it looks kind-of-like-this :
Here is a pict of the case - open - the front of the case is in the middle & the back is on the left ;
The 2 CPUs have fans with shrouds & GPU is Quadro FX3700 (single slot with 1 fan).
- will mount the new fan near the front of the case at the end of the expansion cards - label 'fan' in pict
- thefront square 'grill' is silver (galvanized steel)
- 2 CPU HSF - shrouds are green - left side - middle
- GPU is just below them - stock Quadro FX3450 has a green plastic retainer clip
- the RAM is upper left
- DVD to the upper right
- PSU is on bottom - walled off - stock / OEM
This is not my exact system - mine does not have the HDD cover - solid green square plastic to the right of CPU shrouds

• will remove the black card - end bracket to mount the fan there - between the 2 green plastic 'uprights' - labeled 'fan' in pict
• will make power adaptor : dell proprietary 3-pin (see first pict) ignoring the tach_signal-pin _to_ 4-pin Molex drive power (2 - 12V pins)

? Where to place the sensor on the wire end (the whole purpose of the modification)?
1) between the GPU & below the 1st CPU on the back of the GPU
2) between the GPU & below the 1st CPU on the MoBo
.
? noob ? will anything on the MoBo / GPU get hot enough to melt the sensor wire ?

• I) advice on the wire type / shrink wrap specs ?
• II) How do I 'mount' the sensor wire where I want it ?
• III) Any advice about anything I haven't thought of ?

Thanks in advance

There'll be hardly any current flowing to the thermistor so you can use very thin wire; AWG 22 is overkill for that sort of thing. I have 4 amp fans on 22 AWG.

Shrink wrap is purely dimensional... most of it shrinks to 1/3 original diameter so calculate according to the size of wire you choose.

The only things very hot on your mobo will be heatsinks, so keep the wire away from them and you should be good. Thermistor placement will be a matter of trial and error.

I'm hesitant of changing wire length like this. Sometimes it works fine and sometimes it changes the reading. Have you tried using the fan as is and placing the sensor on the hottest component it will reach? You may not need to lengthen it.

Thanks for the replies:
LennyRhys,
you are quite right - almost no current ;
on the vendor's ebm-papst site http://www.ebmpapst.us/en/support_1/faq/faq_2.htmlhttp://www.ebmpapst.us/en/support_1/faq/faq_2.html it said
"10. What’s the farthest distance the NTC resistor can be from a Variofan?
Fifteen (15) feet. You must use a twisted pair of 24 gage wire.
" , I figured that the price difference for 18 inches would be negligible ,

and the slightly thicker wire would be easier for me to crimp / solder & position in the case.
.
doyll,
the fan is from a DELL 4500 CPU / HSF , and has the thermistor attached - see the upper 2 picts.
I am adding a wire to it.
So, it would have origainally had warm air flowing over it for the thermistor to sense ;
I am going to use it as an intake for the front of the case , so it would have cool air flowing now.
Hence, I will de-solder the sensor to put it at the end of wires ;
then place the sensor (probably) between the 1st CPU & the GPU where it will get warm.
.
?Qusestions about the exact nature of the wire required - the ebm-papst faq was silent
does it have to be a "high-termerature" capable insulation?
?Also, is my proposed / guessed location a good place for it?
.
Thanks again

Sounds good. Maybe cut wire a few inches away from sensor so as to not apply too much heat to it.. or add wire from fan end? Might want to make lead long enough to fit most anywhere around CPU or GPU in case you need more heat to get desired fan speed.

That's about where I put the intake fan on my old 670. The stock fans were loud as heck so I took the VRM wire a fan and spliced it into the stock fan ports as a bypass. Also bypassed the RAM fan at the top by bridging the two side pins (IIRC) since I was running 6GB in it and it wouldn't boot without the RAM fan which I did not have.

Even with the intake fan it'll probably run a little warm near the middle 3.5" bays. Mine always was pretty toasty in that area but that was without the stock exhaust fans installed so it may not matter if you're still using the default deltas. Replacing the TIM might help since it's probably chalk at this point.

If you're not using the PCI/PCI-X slots you can also remove the backplates and rig up an intake fan on the back with zipties.

grumperfish,
thanks for the input.
The Dell Precision 670 Workstation RAM - Fan is my next / concurrent project.
Your info about 'shorting' the 'outer' 2 contacts on the MoBo Ram_Fan is welcome news.
The same idea is found here http://forums.cnet.com/7723-7586_102-261994/dell-precision-470-memory-fan-problem/
I plan on 'shoe-horning' in a 60 mm thermistor fan, either Vantec or ebm-papst , in the upper corner , exiting out the back, for this, powered from a 4-pin peripheral / adapter ; & don't have the actual mounting nailed - down yet.
The DELL W5620 or WC417 50mm memory fan & green plastic shroud is not available anymore.
Will probably model in FreeCAD http://www.freecadweb.org/, then find a 3D Printer service.
?Any good recomendations?
-Will eventually post a separate topic relating to this.
...
I am researching the Dell Molex # 50-57-9403 'special' 3-pin fan connectors, in order to make the adapter.
...

I didn't have the memory fan module either so I simply rigged up a fan blowing on the RAM chips. A 3D printer might work better but zip-ties worked fine.

If you're running above 4GB IIRC you'd need a fan (and you may want one anyways as it gets warm up there), however you can simply bridge the farthest two pins on the three pin connector from your last picture. I had a spare connector so I just bridged the two wires on the sides, however any pin-style connector will work so you can strip a 3-pin fan connector or front-panel connector for the job.



If you want to bypass the main fans or use a fan controller, you can connect an RPM cable from any running fan to the two lowest pins on the two fan connectors in the top-left by the RAM slots.