Very basic question from a newb

[Codyhtml]

if it is a dell then it probaly more hassel then it is worth don't use it but also be careful wth them they ground throgh there case so if you touch it when something it making it ground then it can give you a nasty shock (it has happened to me ) also if it had 3 wires it was probably a motherboard plug but the comp psu would still give good voltage and plenty of current and you could run 5v things too if you wanted to

 

[Adverse]

OK, here's the deal now:

I have the fan hooked up to a 13.8V Regulated power source with a multi-resistor switch in the circuit. The thing is, on the lowest setting the fan still runs too fast.

In addition to this, the fan stops intermittently only to restart when i touch the power source or switch...

Would lowering the voltage of the power source (getting a diff one) be a better way to regulate the rpm of the fan?

Thanks a lot!!

 

[audioguru2]

Hi Adverse,
The problem with using a resistor to reduce the voltage to the fan is that the voltage changes backwards to what it needs. It the fan slows down for some reason, it draws more current which causes more of the supply's voltage to be across the resistor, not the fan. Hence, even lower speed. You need a constant voltage with the ability to change it.

Why not make an LM317 variable voltage power supply? It will need a minimum of 14VDC input for a maximum of 12V output. Powering both fans with an 8V output, it will just get warm without a heatsink.  http://www.electronics-lab.com/projects/power/010/index.html

What does your defective meter read with the regulated 13.8V supply?

 

[Adverse]

i used my dad's meter and with the load it read 13.6 i think.

BTW i'm only running one fan now.

 

[Alun]

PWM is the best way to control the speed of a motor but I wouldn't bother for a fan as it's such low power and the torque isn't critical. A comparator or pair of transistors set up with a potential divider with a thermistor can turn a fan on/off with varying temperature of you could use this simple circuit that operates the transistors in the linear region to make the fan spin faster with increasing temperature.

I would normally warn people against circuits like this but it ok to control the speed of a 150mA fan motor like this. The only really big issue with this circuit is consistency because different fans and transistors will behave differently  so you might have to experiment with different resistor values but as you're only building one it shouldn't be a problem.