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|30th June 2002, 17:58||#1|
Hi, I'm planning on making a rheobus/stat/dunno how it's called for my fans..
At this moment, I'd like to control 4 Thermaltake 80mm fans.
On the fans is written:
DC-12V - 0,18 Amp
Which potmeters should I buy to control the fans (from 5v to 12v or sthing) (or it can start at 0v, but I think they only start spinning @ a certain voltage)
Anthro? Help me out
|1st July 2002, 11:49||#2|
Re: Potmeters question
12v 0,18 amp -> P = U.I
so we get 2,16 watts/fan
of you want to control the fans with one knob, take a 10 watt pot (wich are expensive )
if you want 4 knobs ( 1 fan/knob) 2 watt modells will do.
now calculating resistance
ok here we go:
we will name the fan : R2
the pot we will name : R1
total current ( 0,18 Amps @ 12volt ) : I
now we make a scheme:
wich gives :
R2 = 12/0,18
R2 = 66,6 Ohms
now we can calculate the pot's max resistance
R = U/I
now we take U = 7 ( 12 - 7 = 5 (start voltage))
I remains the same ( 0,18)
R = 7/0,18
R = 38,8 ohms
so you need a 2 watt 38 ohm (or nearest value) pot
so you get a pot ( 38 ohm) in series with a 66,6 ohm fan.
but you can do it the easy and cheap way... buy yourself a chip regulated rheobus ~10 watts model you can get it at loveno.be ( 17 euro i think)
but i can make it also @ 12,5 euro
you can solder it yourself if you like
|1st July 2002, 17:41||#3|
ok, tx for the calculations..
I'm in a lack of money atm, but I'll c..
Btw is it possible to connect ccfls to potmeters so you can change their intensity? (on/off isn't enough for me, and my green ccfl in the bottom of my chieftec is way too bright, my hands are green at this moment )
edit: (686 BEF) € 17.00 for 1 rheobus..
I need 8 of them... too much money to handle
|3rd July 2002, 05:36||#5|
So, let me get this straight, if I buy 4 "2 watt 38 ohm" (or nearest value) pots, then I'm settled for my fans?
Does that need heatsinks (as seen on some rheobusses?)
How much does that cost approximate?
And could you do a quick calculation on what pots I should use for ccfls? (or is it the same, but then 5 watt 38 ohm ?)
|3rd July 2002, 11:45||#6|
you can't place place heatsinks on pot resistors cuz' they are round
Voltage regulators on the other hand DO need heatsinks, but you don't need those for what you're doing.
|3rd July 2002, 16:52||#8|
with a potmeter, you simply make the resistance between your molex and your fan variable so it gets less/more voltage, with a voltage regulator, you can make an electrical scheme that does the same thing, not by changing the resistance, but by directly changing the voltage. You still need potmeters if you use voltageregulators though, otherwise you can't affect the voltage you get from the voltageregulator, you would just get the voltage the VR is built for
(eg. 7812 -> 12V).
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