# Thermal Switches for controlling fans



## streetfighter 2 (Aug 13, 2010)

I have about 20W of fans and I'd prefer that they switch off when they're not needed to save power.  The traditional manual rheobus style fan controllers are out of the question because I completely loathe doing something manually that should be automatic.  Additionally having each fan wired to its own individual thermal control seems like a lot of extra wires and a huge pain in the ass.  Finally, fans that have a built in temperature control won't completely shut off and they don't read the temperature of the parts I care about.  I looked around for a solution to my problem and thermal switches seemed to fit the bill.  I like low thresholds because if something is hot now it's going to be hotter later so I picked this one:
http://www.frozencpu.com/products/9...at_40C_Off_at_32C_or_Less_.html?tl=g47c17s422

It has the perfect temperature on/off range and it's at the price I want too!  I plan to put two of them in parallel so that one is checking my GPU and one is checking my CPU then wire all of my fans to them.  That way if my GPU and/or CPU exceeds the threshold then 20W of additional cooling whoopass kicks on.

My only problem is that the thermal switches are the probes themselves and therefore a good bit harder to position where I need them.  I'm figuring I could thermal tape one to the base of my CPU's heatsink and superglue the other one on top of the GPUs fan shroud.  Though the CPU's switching behavior should be pretty precise I'm concerned about the GPU one because of the relatively poor placement of the thermal switch.

Does anyone have a suggestion on how to accomplish what I want?  Perhaps even another type of thermal switch with an external thermal probe.


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## mlee49 (Aug 13, 2010)

It looks small enough to put on the base of a heatsink, but that would just read the temp from the base, not the actual cpu temp.

It sounds like you want an automated solution which would require software to monitor temps of the cpu/gpu and power on specific fans accordingly. 

So manual switches are out of the question?  Just have the additional fans connected to a PCIE slot switch or front panel switch?  Then you could just monitor the temps yourself and flip the switch when you want.

Edit, heres something you may like:

http://www.frozencpu.com/products/8...ermal_Fan_Controller.html?tl=g47c17s422#blank

super low threshold at 30º


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## streetfighter 2 (Aug 13, 2010)

mlee49 said:


> It looks small enough to put on the base of a heatsink, but that would just read the temp from the base, not the actual cpu temp.



Yeah, this is true.  I was hoping it would be close enough though...



mlee49 said:


> It sounds like you want an automated solution which would require software to monitor temps of the cpu/gpu and power on specific fans accordingly.
> 
> So manual switches are out of the question?  Just have the additional fans connected to a PCIE slot switch or front panel switch?  Then you could just monitor the temps yourself and flip the switch when you want.



Yes, rather unfortunately manual switches are out of the question.  It may sound unreasonable but I've gone to great lengths to automate things on my computer/cars/house and so on.  It's nice when things just work and I don't have to worry about them.



mlee49 said:


> Edit, heres something you may like:
> 
> http://www.frozencpu.com/products/8...ermal_Fan_Controller.html?tl=g47c17s422#blank
> 
> super low threshold at 30º



I got the specs from another site and apparently it can only run a combined 1A worth of fans which doesn't give me a lot (if any) headroom unless I buy two. Also the temperature range does seem narrow even by my standards.  Still this does appear to be a valid alternative to the thermal switches I proposed earlier.

What I'd really love is a way to control my external fans in software (other than speedfans limited ability to control the 3 fan headers on my mobo).  The way I see it is this is like using a nuclear bomb to hunt squirrels.  Nevertheless I looked into it and came up with an Arduino Board for a USB interface, a custom high amp rheobus circuit and of course some software to control the fan.  It's not that I'm not up to the task, but this method is a minimum of $60 and a disturbingly large time investment for an otherwise simple problem.


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## streetfighter 2 (Aug 14, 2010)

Well after taking a look at various possibilities and even drawing a circuit I've arrived at five options:

*1)  Two thermal switches wired in parallel and attached to GPU and CPU* (cost: ~$25)
http://www.frozencpu.com/products/89...7c17s422#blank

Pros: cheap; easy install; supports 8A worth of fans
Cons: static temp limits give little control; placement dictates performance

*2) Two Thermal Fan Controllers* (Cost: ~$35)
http://www.frozencpu.com/products/8...ermal_Fan_Controller.html?tl=g47c17s422#blank

Pros: Easy install; relatively cheap
Cons: extremely limited control; controls 1A of fans per unit; bulky because of two units

*3) DEV-09669 USB Relay Controller* (Cost: ~$65)
http://www.sparkfun.com/commerce/product_info.php?products_id=9669

Pros: switch on/off as many fans as i want; software switching of fans; useful for other crap too!
Cons: difficult install with need for custom software; expensive; bulky

*4) DIY thermal fan controller* (Cost: ~$35)






I opted to use the AD22105AR instead of the TMP01 because it seemed simpler for my purposes.  Unfortunately I couldn't simulate the circuit because there is no PSPICE model for the AD22105AR.  If anyone actually wants to build this circuit you should pick a BJT that has a current rating high enough to drive whatever 5V relay you pick.  You'll also want to add a 1k resistor on the out pin (2) of the AD22105AR.  The diode, BJT and relay are all generic ones I dropped into the design because I couldn't simulate it and decided not to bother calculating the values I actually needed.  The resistors R2 thru R5 are stand-ins for actual fans.  It's only showing 4 fans in the circuit but it's trivial to add switching control for more.

Pros: switch more fans than non-DIY thermal controller; fairly cheap; more customizable
Cons: gettings parts; difficult assembly; bulky temperature sensor with many wires

*5) DIY fan relay circuit* (Cost: ~$60)
Using an Arduino Duemilanove and some custom relay circuits

Pros: lot of extra features; switch many fans; computer control
Cons: expensive; time consuming; more bulky

At this point I'm leaning more towards option 3 (the DEV-09669) because it seems like it will be much more useful in the future.  However I haven't looked at how bad coding for it will be so I'm not absolutely certain yet.


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