Greetings Guys!

I have a question on controlling 2 DC Fans' speed with potentiometers!

I want to wire them up in parallel connection , more details :

2 similar DC fans : 12 volts and 2.5 AMPS for each
1 adapter : 12 volts and 5 AMPS
2 potentiometers for each of the fans!

But I think something is wrong with it ; as it is obvious (according to Ohm law) R is in contrast with I.It means when I want to change the resistance of one of my fans with potentiometer , then the AMPS of the another fan will be increased due to parallel connection! furthermore , it burns out!!!

What can I do about it ?!

Thanks in advance

 

Hello,

The second fan will not burnout due to the fact that the voltage will stay the same.
The fan just takes the current it needs.

Bertus

 

I smell a smoking potentiometer in someones future..

12V x 2.5A = 30 watts

 

Fans such as those sound similar to automotive types, they were typically ran with high wattage resistors switched in for speed control, now they are often done with PWM.
You could also put them both in series across 12v!
Max.

 

for controlling fan speed, u better to go with circuit. using LM2576 with adjustable output voltage.

got through this link

http://www.ti.com/lit/ds/symlink/lm2576.pdf

 

If the fans are brushless DC type, they have a built in controller that may not work right if the series resistance is high, i.e. you will have limited control over the speed, only at the upper range.

The potentiometers will need to dissipate large amounts of power- better to use a rheostat- a fancy name for a power potentiometer, but these are large, expensive and hard to find these days.

 

Thanks a million ...

 

I smell a smoking potentiometer in someones future..

12V x 2.5A = 30 watts

What do you mean by that ?!

 

What do you mean by that ?!

That means you CANNOT use a potentiometer as it will go up in smoke almost instantly.. They are rated up to a few watts max and cannot handle the dissipation.
These aren't uber small computer fans you are talking about here.

Hence the suggestion above for a rheostat.. But wait till you see the prices for those in the sufficient rating.

 

I would use a pwmcircuit using a 555 timer.