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12 Volt Thermal Fan Regulator (temperature-controlled supply)

temperature fan electronics speed control temperature controlled

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#1 Anonymiss

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Posted 27 November 2014 - 05:41 AM

Three years ago...

I'd been looking for a thermally-controlled 12 Volt fan supply for a while but I couldn't to find one that suited my needs. The commercially available controllers for use in computers tend to give their maximum output around 35°C or 40°C which was too high for me. I needed the output to hit 12 Volts at closer to 25°C.

So I eventually stopped looking and decided to build my own. I hadn't picked up a soldering in years, so I was pleasantly surprised when it worked first time!

I used the Micrel MIC29152BT low-dropout adjustable voltage regulator, which will supply up to 1.5 Amps. At 12 Volts, that's 18 Watts of power so it should handle most fan setups designed for small spaces. (Larger regulators are available, see later on.)

I used the circuit provided in Micrel's datasheet [PDF] as the basis for the design. I replaced one of the resistors with a thermistor, and I substituted a combination of resistor plus potentiometer for the other resistor to give some control over the output.

With my chosen components (see below) and with the potentiometer set to the mid-way position I get 11.8 Volts at 25°C, but it can be adjusted to go as low as 8.9V (at 25°C) or to provide the full 12V at 21°C.

Here's a graph showing the output Voltage over a range of temperatures with the control knob in the min/mid/max positions:
 
Fan regulator output-Voltage graph


After calculating the resistor values and Voltage swings, this is the circuit I finally came up with and used:
 
Fan regulator circuit


And the component list:

IC1 : MIC29152BT/WT Low-Dropout Voltage Regulator
R1 : 620K resistor, 5% tolerance, 0.25W
TH1 : 100K NTC Precision thermistor
VR1 : 470K linear potentiometer
C1 : 10uF 16V aluminium electrolytic capacitor
C2 : 22uF 16V aluminium electrolytic capacitor

Other things required required include: Strip(Vero)board, a heat-sink (21°C/W), some thermal compound (CPU compound is fine) or a pad, an M3 or M3.5 bolt/washer/nut for mounting the regulator on the heatsink (or use a clip), and a control knob if you want to get all fancy. A small case or box to put it all in might also be an idea.

Everything is available from Rapid Electronics (and is linked in the above list). RS Components probably also do them, and Farnell may be able to supply them. Unfortunately, Maplin don't do the 29152, but they do have the other bits including a suitable thermistor (although this does have a lower B-value so the Voltage swing won't be quite as large).

Total cost for the parts [in 2011], including postage but excluding a box and some thermal compound (which I already had from PC-builds), was £11.94 from Rapid (the postage was very nearly half of that).

I built it on stripboard (Vero-board) using this layout:
 
Fan regulator layout


Note the two track breaks which are marked as red dots. The grey lines are wire links.

It looks like this when finished (may not match the above layout exactly because, well, you know...):
 
Fan Regulator Complete


The heat sink in the picture is one that I stripped out of a broken HD-recorder, so it's kind of over-size and it doesn't match the one in the component list.

The thermistor itself is tiny, maybe 2mm across. I decided to mount it in a 2.5mm jack plug for robustness, and so that I could run a cable to where I want the sensor without having to mount the entire circuit there.
 
Fan Regulator - Thermistor Mounted


The thermistor is the tiny blue dot.

Alternatively, the thermistor could be mounted directly on the strip board as long as the entire device is mounted inside the grow space. For PC-grows it could probably be mounted in a drive bay cover, or on a PCI slot cover, by using the threaded shaft on the potentiometer. Close to the exhaust fan would also be a good place too.

That's about it really. Overall I'm quite pleased with it (not least because it works!), and it suits my situation and needs.

Good luck if you decide to make one!

--

Want more Amps and Watts?

Other regulators with higher maximum current ratings are available for power-hungry users; the 29302BT will provide up to 3 Amps (36W at 12V), the 29502BT can handle 5 Amps (60W at 12V), and the 29752BT will go up to a 7.5 Amps (that's 90W at 12V, which should be more than enough for anyone!). These all have the same pinouts as the 29152BT so they can be used as drop-in replacements, but you'll likely need a bigger heatsink.

--

I made this (and wrote most of the above post) over three years ago, and it's been in almost-continuous use ever since. I've upgraded it with a 5 Amp regulator and larger heatsink to cope with more fans (six), and I'm currently running it off a 16 Volt, 5 Amp laptop supply and it's still going strong.

If you use a supply greater than 12 Volts (the maximum allowable is 26 Volts) then be aware that the circuit's output Voltage is not limited to 12 Volts and can equal the input Voltage. This hasn't broken my fans (at 16 Volts) although they don't all behave in the same way, with some getting faster as the Voltage goes over 12 Volts, and some not.
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#2 WanderinBloke

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Posted 27 November 2014 - 04:24 PM

Awesome. I love that we have you here, @Anonymiss 

 

Obvious question: If you build it can we buy it? You're obviously very good at this sort of stuff, are you interested in selling it?



#3 Vador

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Posted 27 November 2014 - 10:48 PM

Thanks for sharing missy, could be just what I need in my veg tent

#4 Anonymiss

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Posted 28 November 2014 - 07:34 PM

Awesome. I love that we have you here, @Anonymiss


blush2.gif

Obvious question: If you build it can we buy it? You're obviously very good at this sort of stuff, are you interested in selling it?


This is difficult... I've been asked before and I still struggle to know what to say.

I don't mind actually doing the work, but I really don't know how to handle the rest of it. Firstly, there's going to be a paper trail for the money and, secondly, it would require that people send me an address so that I can deliver the finished item.

The first isn't a show-stopper — The components are cheap enough and I'd probably be happy if people made a donation to a children's charity instead of sending me the money.

But the second is problematic — I'm really not at all comfortable with the idea of knowing people's addresses (be they 'safe' or otherwise), and I don't see a way around that.

[This is also why I've never entered, or run, a competition.]
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#5 WanderinBloke

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Posted 28 November 2014 - 10:55 PM

blush2.gif


This is difficult... I've been asked before and I still struggle to know what to say.

I don't mind actually doing the work, but I really don't know how to handle the rest of it. Firstly, there's going to be a paper trail for the money and, secondly, it would require that people send me an address so that I can deliver the finished item.

The first isn't a show-stopper — The components are cheap enough and I'd probably be happy if people made a donation to a children's charity instead of sending me the money.

But the second is problematic — I'm really not at all comfortable with the idea of knowing people's addresses (be they 'safe' or otherwise), and I don't see a way around that.

[This is also why I've never entered, or run, a competition.]

 

Bitcoin to you or a charity donation, either would be cool and fairly anon. The addresses thing is the sticking point. :-/



#6 Vador

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Posted 29 November 2014 - 10:29 AM

Just make one wibble, parts are easy to get and even easier to put together, should be a fun project

I'm thinking you should also be able to take the circuit as it is and swap the thermistor for a humidity sensor and it should then work on detecting RH, shouldn't need to change anything else, what do you reckon @Anonymiss

#7 Anonymiss

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Posted 29 November 2014 - 05:53 PM

I'm thinking you should also be able to take the circuit as it is and swap the thermistor for a humidity sensor and it should then work on detecting RH, shouldn't need to change anything else, what do you reckon @Anonymiss


I don't see why not :)

You may need to change the R1 + VR1 combination if the new sensor's resistance is different to that of the thermistor.

Vout = 1.24 x ( 1 + ((R1 + VR1) / TH1 ))

Alternatively, (R1 + VR1) = TH1 x (( Vout / 1.24 ) - 1 )

The actual output range/swing will depend on the rate of change of the sensor (B-value, in thermistor terms), with higher values giving larger variations in output.
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#8 Vador

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Posted 29 November 2014 - 06:09 PM

Excellent I will look into that, thanks
I'm thinking about making a couple of these maybe have one controlling inlet one exhaust in the cutting tent

#9 Anonymiss

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Posted 29 November 2014 - 06:34 PM

You might find attached Excel sheet useful :)

Enter the Thermistor Properties, and the values for R1 and VR1, and it will calculate and graph the output Voltage over a range of temperatures.

You can also use Excel's Goal Seek to function to ask things like, "what value should R1 be to get 12 Volts at 25°C with VR1 in the Mid position?"

Attached Files


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#10 Vador

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Posted 29 November 2014 - 06:35 PM

Legend



Also tagged with one or more of these keywords: temperature, fan, electronics, speed control, temperature controlled

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