Automatic fan regulator help needed

[chrisnasah]

Hi Guys,

New here hope someone can help.

Am looking to do this circuit for one of my noisy sat equipment. The issue am having is i am not able to locate a NTC with 470 ohms rating. I am able to get a NTC with 1K rating.

Now in order to reduce this can i put in a 880ohms resistor before it and have it roughly at the value i want?

Thanks

 

[crutschow]

You could put 880Ω in parallel with the 1kΩ NTC resistor to get 470Ω but the change in resistance with temperature would likely be less then using a 470Ω NTC.

But I think the 1kΩ NTC may work ok by itself. Just change the pot to 10kΩ.

You are aware that the circuit maximum output voltage will be only about 10V, so the fan will never get up to full-speed?

 

[chrisnasah]

Thanks for quick update. Is there any way to improve this circuit and maybe have it output 12v?

So do you think as am not able to get the 470 ohm NTC sensor i could use the 1k ohm without resistor and just change the pot to 10k ohms?

Sorry i dont understand things like this, not sure what effect using 10k ohm for pot will do.

 

[crutschow]

You either need to increase the input voltage to about 14V, or use a low drop-out type regulator to get near 12V at the output.

The resistance ratio between the two resistors determines the output voltage. Thus absolute values are less important than the ratio (unless the resistance gets too high and then the regulator bias currents can significantly affect the output voltage). Going from 470Ω and 4.7KΩ to 1kΩ and 10kΩ keeps the same ratio.

 

[chrisnasah]

thanks alot