DC fan speed regulating question

[sunrise]

Hi guys,
I have buyed Titan TFD-12025M12B DCfan for cooling my amplifier. It has three wires for connecting - red, black and yellow. Black is probably gnd, red is probably +12V and yellow is probably for controling the speed of the fan.
Question - how to control the speed of this fan?

Should i regulate the dc voltage or should i use controling wire (which i would like to do best if possible) and if so - how to use it?
Best regards and thanks for the replies
sunny

p.s. here is the link for their home page but you can't find much there.........http://www.titan-cd.com/eng/dcfan/fa...odel=TFD-12038

[Christer]

More likely it is an output from the fan used to sense the rpm. Most computer fans have those nowadays. So you most probably has to control the speed by adjusting the voltage, or doing something more complex, like PWM.

[BlackCatSound]

The yellow is usually a speed pulse output so a PC can tell how fast its going.

[sunrise]

o.k. - this is probably done by changing the voltage between black and red wire - so the yellow wire is output from the fan that says how fast the fan is rotating - so i have to change the voltage between red and black afterall?
Does anybody know from which voltage it will start to rotate?
regards
sunny

[Christer]

It depends on the fan, but you can usually go down to half the specified voltage without problems. Some fans don't likte that, though, so if you have a variable voltage source, then test at different voltages. The problem is usually to get it to start at low voltages.

Edit:
Often people just add a resistor in series with the fan to get the speed they want, so one possibility is to just experiment with different resistors. Just keep in mind to respect the power rating of the resistors.

[jackinnj]

you get a tachometer -- if it isn't "tachom-a-tating" you have a problem. and while you're at it take a look at National Semiconductor Application Note 292 -- "Applications of the LM3524 Pulse Width Modulator".

[sunrise]

o.k. guys - thanks - it was helpfull.....i think that the easiest will be to use LM317 with a potentiometer and regulate it from 6VDC or so to about 12V or so
thanks again
sunny

[Christer]

Originally posted by sunrise
o.k. guys - thanks - it was helpfull.....i think that the easiest will be to use LM317 with a potentiometer and regulate it from 6VDC or so to about 12V or so
thanks again
sunny

Or even simpler, just an emitter follower and a pot,, since you don't need tight regulation.

[sunrise]

right
thnx
sunny

[Nelson Pass]

The trick is to start the fan with a higher voltage, so that it
gets rotating, and then settle it down to a fraction of the rated
voltage. You can do this by putting a capacitor from Collector to
Base on the voltage follower.

You can get the spped quite low, but you have to watch out, as
dust and age may cause the fan to stop at very low speed
settings.