heat activated cooling fan

this a circuit based on the op amp ic 741. this circuit can be used for cooling fans inside pc or an amplifier.it will reduce the unwanted usage of the cooling fans. please rate it.........

Step 1: Parts list

1 x LM741 IC
2 x IC base (holder)
1 x 10k thermistor 
2 x 10K resistor(brown black orange)
1 x 1k resistor(brown black red)
1 x 680r resistor(blue grey brown)
1 x 10k variable resistor (preset)
1 x BC327 transistor 
1 x 1000uf 25v electrolytic capacitor
1 x 2200uf 25v electrolytic capacitor
1 x a cooler fan or a 12v DC motor
1 x common circuit board

Comments

[steps39]

Hi, I would like to increase the voltage range of the device 5 - 12V so that the fans turn off completely when the PC is cold and then build up to max at about 50 deg is this possible and which resistors control the lower voltage please.

[rocketman217]

will a 100k thermisistor work?

[diy_bloke]

yes it will, but you better increase the resistor with which it makes a voltage divider to 100k as well. With a comparator like this the actual value of the resistors is less important than their relative value

[pcline2]

About how much current do you think this circuit would be able to handle?

[sooraj619]

a 12v 3A power supply (max) the 741 IC burned after this

[pfred2]

What does the 2200uF capacitor do in the circuit? I hate using those spring IC sockets too. They cause so many problems in projects. They're actually more expensive than ICs often too. If I have to socket an IC I use machined turret sockets. They're a lot nicer.

[sooraj619]

2200 uf capacitor is used to reduce ac ripples from a 12v dc transformer when connected as per supply, in case of batteries it is not necessary

[pfred2]

OK. I didn't think it would do much good with a battery.

[coolkids]

can it work just like a cutof in your ac like you set temperature as 24c on your ac and when the 24c is achieved it stops cooling and the blower mode goes on so if excess heat is present in the sorounding then the motor starts working to cool the excess heat

[sooraj619]

(removed by author or community request)

[sooraj619]

the motor that works from 9 - 12v can be used, or use a 9v relay

[sooraj619]

yes