Is there a Full-On/Full-Off Thermostat-type Circuit?

Rory B. · Post by **Rory B.** » Sun Sep 12, 2004 1:20 pm

I am looking for a full-on and full-off thermostat circuit. I would like some fans to be completely off when unneeded, which will be most of the time.
If this is something I could build on a breadboard, that would be cool, too.
And if I could adjust the turn-on temperature, I would like to do that as well.

Tibors · Post by **Tibors** » Sun Sep 12, 2004 1:48 pm

The mCubed TBalancer can do that. Its not a circiut, but a finished product. There are several threads in the Fans & Control forum about it.

Bluefront · Post by **Bluefront** » Sun Sep 12, 2004 2:02 pm

DigitalDoc5 or 5+ does just that. And it can individually control up to eight fans.......plus register eight different temps on an LCD screen.

The 5+ version seems to be a better setup as the fan turn-off point can be set lower than the turn-on point. That eliminates constant cycling if your temps are running close to the set point. I'm using the earlier version which works fine. These are available various places around $25/$30.

Rory B. · Post by **Rory B.** » Sun Sep 12, 2004 8:18 pm

I only need a single channel. Can you give me a link to the mCubed thing?

Rory B. · Post by **Rory B.** » Sun Sep 12, 2004 8:23 pm

Actually, I found it. I may go with that if I can't find a way to build something smaller that will do the job for me. Does anyone know of an electrical circuit, not a $50+ product that will be extremely overkill for my application?

silvervarg · Post by **silvervarg** » Mon Sep 13, 2004 12:20 am

Fancontrol buildt something similar in this thread:
http://forums.silentpcreview.com/viewtopic.php?t=11237
Unforutnately the images does not seem to work anymore.

The basic thing is a comparator with a NTC on one input and a trimpot on the other to set the temperature. The output controls a transistor (darlington) to turn the fan on/off.
Fancontrols circuit was a bit more comples to make the off temperature setting lower than the on temperature.

I can't remember more details, but drop Fancontrol a mail to see if he can republish the images.

peerke · Post by **peerke** » Mon Sep 13, 2004 8:01 am

Bluefront wrote:DigitalDoc5 or 5+ does just that. And it can individually control up to eight fans.......plus register eight different temps on an LCD screen.

The 5+ version seems to be a better setup as the fan turn-off point can be set lower than the turn-on point. That eliminates constant cycling if your temps are running close to the set point. I'm using the earlier version which works fine. These are available various places around $25/$30.

That's a very interesting device but for me it has three drawbacks:
It uses a 5,25" drive-bay and I don't have one to spare.
In the Netherlands it seems to be only available in beige (would like black).
The price overhere is â‚¬ 80,= which is twice the price you quote.
Does anyone know of an alternative with the same functionality?

BTW Who is the manufacturer of the Digidoc? I can only find resellers.

Gholam · Post by **Gholam** » Mon Sep 13, 2004 8:56 am

IIRC, Digital Doc series of fan controllers is made by Innovatek - the company responsible for the much more expensive Fan-O-Matic.

Rory B. · Post by **Rory B.** » Mon Sep 13, 2004 9:52 am

I'll contact Fancontrol. Perhaps a group buy of PCBs is in order, since a thermostat-type controller allows the fans to completely shut off when unnecessary, totally eliminating the noise. Then my silent PSU can do its thing when one very slow fan is enough. And not everyone has 8 fans to control and thus Fancontrol's solution is much more reasonable than buying the expensive DigiDoc 5. Perhaps an adaptation of the circuit could allow the power for the circuit to come from the 12v rail and the power for the fan could come from the 5v rail.

Gooserider · Post by **Gooserider** » Tue Sep 14, 2004 1:25 pm

The Digidoc is made by a company (Asian I believe) with the rather confusing name of "MacPower". AFAIK they have no connection to Innovatek.

IMHO the Digidoc is a nice product in concept, except that it only does on / off toggling control, rather than any sort of thermostatic speed control. I don't know why MacPower can't create a version that does speed control as that would be a real killer combo for sure.

Gooserider

Becks · Post by **Becks** » Tue Sep 14, 2004 1:34 pm

Where do you need a full on/off switch? I have hte mcubed thing and for awhile had my harddrive's fan set to full on/off when it reached 43C it turned full on, otherwise it would be full off... sounded like a neat plan.. problem is when it gets to 42C... its off, goes to 43C full speed for a few seconds and temp drops to 42C and it turns off.. 1/2 second it heats up and hits 43 and fan turns on for a second until it drops to 42... see the problem?

THe fan kept ramping up and down every few seconds and was VERY annoying, it would have been better just to have full speed all th etime, rather than hearing it spin up and down constatnly.

Might not apply to your use, but i'd keep it in mind.

Post by **MikeC** » Tue Sep 14, 2004 7:58 pm

Becks wrote:Where do you need a full on/off switch? I have hte mcubed thing and for awhile had my harddrive's fan set to full on/off when it reached 43C it turned full on, otherwise it would be full off... sounded like a neat plan.. problem is when it gets to 42C... its off, goes to 43C full speed for a few seconds and temp drops to 42C and it turns off.. 1/2 second it heats up and hits 43 and fan turns on for a second until it drops to 42... see the problem?

THe fan kept ramping up and down every few seconds and was VERY annoying, it would have been better just to have full speed all th etime, rather than hearing it spin up and down constatnly.

Might not apply to your use, but i'd keep it in mind.

SilentTek (AOpen mother board utility) offers the same option -- off/on at selectable temp. It only works well if the fan never has to ramp up. This means a cooling system that's good enough to run fanless most of the time and a very high turn on temp. Otherwise, it's really annoying.

peerke · Post by **peerke** » Tue Sep 14, 2004 9:09 pm

Gooserider wrote:The Digidoc is made by a company (Asian I believe) with the rather confusing name of "MacPower". AFAIK they have no connection to Innovatek.

IMHO the Digidoc is a nice product in concept, except that it only does on / off toggling control, rather than any sort of thermostatic speed control. I don't know why MacPower can't create a version that does speed control as that would be a real killer combo for sure.

Gooserider

Thanks for the heads-up Gooserider. That's one item less on my shoppinglist! Incredible how a manufacturer comes so close to a great product and then fails misserably

. How difficult could it be to make a three step version with off, slow and max?

rperezlo · Post by **rperezlo** » Wed Sep 15, 2004 1:35 am

peerke - take a look at the T-Balancer.

http://www.mcubed-tech.com/eng/index.htm

I think it does what you want. The fan on/off switch problem is easily solved with this controller and in fact I have 2 fans off most of the time.

Rory B. · Post by **Rory B.** » Wed Sep 15, 2004 7:41 am

Fancontrol's circuit is set up to turn on at 38C and then not turn off until things are down to 28C. The short-cycling you describe should not be an issue. I will also be dealing with case air temperature which won't change as quickly as an individual component. I imagine I could adjust to a smaller range of temperatures with a different resistor or something. The machine I will be building this into is not necessarily a silent rig but I want it to be quiet until the cooling is actually needed, like at a LAN party when the action heats up. (winkwinknudgenudge)

Unfortunately, Fancontrol has not contacted me in reply yet.

cpemma · Post by **cpemma** » Fri Sep 17, 2004 11:48 am

There's a thermostatic switch with hysteresis (a gap between on & off temperatures so you don't get the rapid switching Becks experienced) at Bill Bowden's site, or a simpler one that works OK in simulation (but untested so far with real parts) here.

Rory B. · Post by **Rory B.** » Sat Sep 18, 2004 12:00 pm

I build high-fidelity loudspeakers all the time from computer simulations, from cabinets to crossovers, and they work fine, so I will go ahead and use this easier comparator circuit with transistor. Since you seem to know plenty about this, what role does R1 play? That is, could I replace it with a 100k pot and set the temperature?

silvervarg · Post by **silvervarg** » Sun Sep 19, 2004 10:54 pm

I believe R1 is an NTC resistor, so it changes with temperature. For testing the circuit it would be easier to put in a 100k pot as you suggested.
VR1 is supposed to be a pot, and this is what you use to adjust the temperature threashold.

Rory B. · Post by **Rory B.** » Mon Sep 20, 2004 5:18 am

oh, i see. It's the thermistor. That makes sense. I thought it was supposed to adjust the hysteresis range. So I have to ask, what is the hysteresis range of this circuit? (that is, if anyone knows)

cpemma · Post by **cpemma** » Mon Sep 20, 2004 11:39 am

The simple simulator I used for the linked single op-amp circuit won't let me make fine adjustments to temperature, but hysteresis is around 5°C, determined by R4 and the temperature setting (higher R4, less hysteresis).

R1 is indeed the thermistor, 100k @ 25°C NTC, but other values could be used, changing VR1 to match.

Using R4=200k gives a "comes-on" voltage of 6V at the non-inverting "+" input, "goes off" voltage = 6.45V, so you could work things out knowing the thermistor temperature/resistance curve & Ohms Law re potential dividers.

There's an explanation of the circuit I belatedly added over the weekend which may help with parts, etc.

fancontrol · Post by **fancontrol** » Tue Sep 28, 2004 11:51 am

My ears were burning so I thought I'd check in.

It sounds like you've got all the info you need from cpemma's post. The only difference in my design was using a p-fet to switch the fan. That way i could put a big 'ol resistor across the fet to have the fan switch to low speed (instead of off) and not screw with the tach signal. In that version i also put a cap across the thermistor so the fan would get kick-started at power-up.

Let me know if y'all want the schematics posted again; they're around here somewhere.

Rory B. · Post by **Rory B.** » Wed Sep 29, 2004 8:34 am

More information can't hurt...

(famous last words)