Author Topic: I came up with this temp controlled fan circuit.  (Read 1448 times)

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Offline Refrigerator

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I came up with this temp controlled fan circuit.
« on: June 11, 2015, 04:14:25 pm »
So i was out of thermistors but i needed something to turn on a fan when temperature's too hot so i quickly came up with this simple circuit which uses a diode to sense the temperature:
http://gyazo.com/d664fff48508359a40c04e13479ac83e
The circuit was tested on a breadboard and can be adjusted to work with any silicon diode using the 5k pot which also adjusts at what temperature the fan turns on.
The fan does ramp up quite quickly when giving it a brief blow of hot air ( set to 100oC @ ~10cm using 1N4148 ), might not be the best circuit but it gets the job done quite well.
Decided to post this here in case anyone needed it. would also like to hear what you guys think of it.
Just started a blog at http://brimmingideas.blogspot.com/ . Not much in it as of now but more is sure to come :)
 

Online macboy

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Re: I came up with this temp controlled fan circuit.
« Reply #1 on: June 12, 2015, 01:01:06 pm »
One problem may be that the VBE of Q1 will actually change quite similarly to VF of D1 if both are at the same temperature. So this may work well if D1 is a remote temperature sensor, with Q1 kept relatively cool, but with both mounted in the same hot space, it might not work at all.
 

Offline Refrigerator

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Re: I came up with this temp controlled fan circuit.
« Reply #2 on: June 12, 2015, 03:24:14 pm »
One problem may be that the VBE of Q1 will actually change quite similarly to VF of D1 if both are at the same temperature. So this may work well if D1 is a remote temperature sensor, with Q1 kept relatively cool, but with both mounted in the same hot space, it might not work at all.
Yes, as i said it's not the best circuit out there but when the temperature sensor ( diode ) is mounted remotely it does work very well.
This circuit from start to full speed gets in about 15oC but if a quick ramp up is needed the second transistor can be modified by connecting the emitter to ground and connecting the fan in between the supply and collector.
http://gyazo.com/a938d6d9342c326f5a9762de5edf3482
This way the circuit ramps up right when the set temperature is reached but the supply must not exceed the rated fan voltage.
Just started a blog at http://brimmingideas.blogspot.com/ . Not much in it as of now but more is sure to come :)
 

Online dom0

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Re: I came up with this temp controlled fan circuit.
« Reply #3 on: June 12, 2015, 04:23:39 pm »
One problem may be that the VBE of Q1 will actually change quite similarly to VF of D1 if both are at the same temperature. So this may work well if D1 is a remote temperature sensor, with Q1 kept relatively cool, but with both mounted in the same hot space, it might not work at all.

Yes, that's in fact a requirement of circuits like these, only one of the BE junctions in the circuit is in contact with whatever has to be kept cool.
,
 


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