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Joe's simple fan control - untested

Started by joecool85, May 17, 2012, 04:07:52 PM

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**This circuit is untested, unverified and not recommended for anything other than testing purposes!**

This is what I came up with for a simple temperature driven fan controller.  It is a fan controller I worked on, based on the Temperature Controlled Fan I found online.

This is good for a maximum of 1.5amps, but really you should keep it below 500ma to keep it reliable.

In this version, R1 is a 10K NTC thermistor (shown in schematic at 20C, which is 12.5k).  Adjust R2 for the turn on temperature and R4 for the full speed temperature.  Fan is a 12v PC fan that draws 0.11 amps.

Note that if you change R4 (full speed temp) you will need to re-adjust R2 (turn on temp).  Due to this behavior, I suggest using trim pots for R2 (5k) and R4 (500R) and adjusting R4 (full speed temp) first and then R2 (turn on temp).

Circuit behavior also changes upon load of fan, IE 0.11 amp fan will have different temp ranges than 0.25 amp fan.

*Note: I have not actually built this circuit, only played with it in LTSpice.

**Note #2: I just noticed in some more simulations that the values change if the fan isn't exactly 0.11 amp, I don't know in practice how much it will matter, but it is something to consider.  For a controller capable of high current (up to 1 amp) that doesn't care what the amperage of the fan is, see my new 12v DC Fan Controller (LM317)
Life is what you make it.
Still rockin' the Dean Markley K-20X


Calculated temperature data

R2 = 5K , R4 = 0R

4.5v @ 0C(32F) / 12v @ 20.3C(68.5F)

Delta T = 20.3C(68.5F)


R2 = 5K , R4 = 1K

4.5v @ 12.5C(54.5F) / 12v @ 49.8C(121.6F)

Delta T = 37.3C(99.1F)


R2 = 0K , R4 = 0R

4.5v @ 18.1C(64.6F) / 12v @ 41.2C(106.2F)

Delta T = 23.1C(73.6F)


R2 = 0K , R4 = 1K

4.5v @ 32.4C(90.3F) / 12v @ 75.7C(168.3F)

Delta T = 43.3C (109.9F)
Life is what you make it.
Still rockin' the Dean Markley K-20X