Panaflo M1A w/rheostat

[beatle]

I'm planning on getting an Alpha 8045 w/a Panaflo M1A. I'll then attach a 5 watt, 100 ohm rheostat to the fan to tone it down when my room is cool or the comp is idle. How quiet will this fan get when turned down with a rheostat, I wonder. Down to L1A levels? That's my idea.

 

[HouRman]

I use a rheostat from Radio shack, I talked with a guy who's an electrician who helped me out when I chose mine but here's some useful information.

Go for at least a quarter of the power the fan uses, so for a 80mm delta screamer fan which takes 6.96w use at least a 1.74w rheostat.

Don't pick a rheostat whose resistance is greater than that of the fan's normal resistance. The normal resistance of the fan is 144 divided by the power it requires. For example a 80mm delta fan takes 6.96w so its resistance is 144 / 6.96 = 20.7 ohms. The nearest commonly available rheostat is 20ohms so go for that.

If you use a resistor with too high of a resistance you will most likely stall the Fan.

Technical Info:

Power = Voltage * Current

P = 12 * I
I = P / 12

Its resistance (from Ohm's so-called-law) is:

V = IR
12 = (P / 12) * R
R = 12 / (P / 12)

R = 144 / P

The current flowing in the circuit at any one time with the rheostat resistance at Y, again from ohms law is:

I = V / R

I = 12 / (Y + R)

 

[HouRman]

Oops, to answer your question, yes, with the right rheostat my 120mm fan was able to slow down to almost in-audible levels. For mine I use a chome knob so it's externally adjustable outside the case.

Picture of my Case

 

[beatle]

Ok, the Panaflo M1A has a wattage of 1.49. This means I only need a rheostat capable of 0.3725 watts. No problem. Now for the resistance. 144 / 1.49 = 96.64 or so. So should I get one rated for 100 ohms? It's close but too high. The next highest one I see is 50 ohms, 5 watts. Thanks for the help so far.

 

[HouRman]

if the fan voltage is taken below 6 volts it is likely to stall so if the rheostat resistance is equal to the fan resistance they both have an equal share of the voltage, i.e. 12 between two of them, or 6 volts.

I doubt 100 ohms will stall the fan, I'm using a 25 Ohm rheostat to power a fan that's "Supposed" to stall at around 21 ohms but the fan just slows down. At Radio shack they sell cheap 5 watts or less rheostats for less than $5.

The reason you'd buy a rheostat with more than 5 watts would be to power more than 1 fan, and the 25 watt rheostats can cost up to $25. I'd choose the rheostat that has enough watts, and 100 ohms. Then you just have to mount it on your case or inside, and solder or crimp the negative wires of the fan through the rheostat.