Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Is the 5k pot ok in my attached circuit?

Status
Not open for further replies.

dmcmillen

New Member
My attached circuit calls for a 2k pot used as a variable resistor and I only have a 5k pot. My supply is either 5.2v/400ma or 12v/400ma DC. The output fan is 12v/200ma. The pot works fine using either supply. The problem I'm having is that I don't have enough control of the fan speed. I get off and full speed, but anything in-between is almost non existent. The fan seems to jump from slow to full speed with very little adjustment of the pot. I was wondering if that was because of the 5k pot instead of the 2k pot or perhaps a function of the fan.

I believe I have the pot wired correctly, jumping the wiper to one of the outside terminals.

I would appreciate any suggestions or help. I'm a bit of a novice/dangerous now. It's been years since I did any serious electronics work. Thanks!
 

Attachments

  • Schematic.jpg
    Schematic.jpg
    28.4 KB · Views: 296
Last edited:
What type of fan is it? Some DC fans tend to operate at the same speed, independent of voltage changes. Does the fan speed change much when you go from 12V to 5.2V?

The 5k pot gives you a maximum output voltage range of 18V, thus the pot is somewhat sensitive at low voltages. Changing the 330Ω resistor to 600Ω will reduce the maximum output to about 10V.
 
Now I see a 2k pot and a 330 ohm resistor. The results will be 1.25 volts to 8.82 volts output if the pot is really, really, 2k ohms. (They are almost never exactly what they say they are.) That still says nothing about how the motor will react to being treated that way. Try it and find out. If it doesn't work, a pulse width modulator might be required.
 
crutschow: The fan is a 90mm computer supply fan. The fan does "seem" to run faster with the 12v supply. Am I to understand that using a 600Ω resistor to drop the maximum output voltage to 10v would make the pot more sensitive at the lower voltage, giving me more control over the fan, assuming the fan operates at different speeds with voltage fluctuations (linear across some voltage range)?

The project specs call for using any 12v computer fan.
 
Fan controller

Most of these fans wom't run below about 50% of rate voltage. Most fan speed controllers use a low frequency PWM (30 HZ or so) to get around this. So if you have a 12 volt fan, a 555, and a power transistor you should be able to get 10 to 100% using a 12 volt supply.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top