Thermistor anyone know the anwser?

[FerrariF50]

I was going to build this temperature controled fan the guy says about a 470 Ohm thermistor puts out about 12 volts now if I got one thats 500 Ohm's would it still run at 12 volts knowing that it's going to be hooked to a 12 volt supply of power?

[maha_x]

470Ohm thermistor puts out 12V? At what voltage? I very recentrly thought that same question. The correct ohm to get the 12V down to ... 9V for example is something like 20ohm. I went trough tens of manufacturers (and someone even sent me samples trough mail! All the way to here, Finland), but there just isnt such a thermistor. Ideally youd need a thermistor that goes down to 0ohm at ... say 50C? Allowing full 12V for the fan. And It could have some 50ohm at 20C. Does not exist, or if you find one, let me know.

Also, the A rating of the fan affects greatly how large resistor youd need for that 9V. So youd need to get that thermistor, and a adjustable resistor (whats it called?) in parallel. Then with multimeter you could adjust the whole resistance of the pair to give that allmost 12V at some temp.

[Mord-Sith]

you guys need to build a voltage regulator like this

http://casemods.pointofnoreturn.org/vregtut/tutorial-1.html

r1 would be a constand resisitor and r2 is your thermister. r2s range is directly effected by the value of r1. I would put a trim pot at r1 and adjust it untill you get the right range for r2. I cant tell you if this will work for sure but its alot better than trying to just throw a resistor in line.

[FerrariF50]

btw here is the link to the stuff i want to build.....

http://www.virtual-hideout.net/guides/temp_controlled_fan/index.shtml

[FerrariF50]

On that site what are they building anyway?

Originally posted by Mord-Sith
you guys need to build a voltage regulator like this

http://casemods.pointofnoreturn.org/vregtut/tutorial-1.html

r1 would be a constand resisitor and r2 is your thermister. r2s range is directly effected by the value of r1. I would put a trim pot at r1 and adjust it untill you get the right range for r2. I cant tell you if this will work for sure but its alot better than trying to just throw a resistor in line.

[FerrariF50]

Well the point of it is to have the fan speed slow and speed up without me haveing to touch it.

Originally posted by maha_x
470Ohm thermistor puts out 12V? At what voltage? I very recentrly thought that same question. The correct ohm to get the 12V down to ... 9V for example is something like 20ohm. I went trough tens of manufacturers (and someone even sent me samples trough mail! All the way to here, Finland), but there just isnt such a thermistor. Ideally youd need a thermistor that goes down to 0ohm at ... say 50C? Allowing full 12V for the fan. And It could have some 50ohm at 20C. Does not exist, or if you find one, let me know.

Also, the A rating of the fan affects greatly how large resistor youd need for that 9V. So youd need to get that thermistor, and a adjustable resistor (whats it called?) in parallel. Then with multimeter you could adjust the whole resistance of the pair to give that allmost 12V at some temp.

[FerrariF50]

Well the point of it is to have the fan speed slow and speed up without me haveing to touch it.

Originally posted by maha_x
470Ohm thermistor puts out 12V? At what voltage? I very recentrly thought that same question. The correct ohm to get the 12V down to ... 9V for example is something like 20ohm. I went trough tens of manufacturers (and someone even sent me samples trough mail! All the way to here, Finland), but there just isnt such a thermistor. Ideally youd need a thermistor that goes down to 0ohm at ... say 50C? Allowing full 12V for the fan. And It could have some 50ohm at 20C. Does not exist, or if you find one, let me know.

Also, the A rating of the fan affects greatly how large resistor youd need for that 9V. So youd need to get that thermistor, and a adjustable resistor (whats it called?) in parallel. Then with multimeter you could adjust the whole resistance of the pair to give that allmost 12V at some temp.