Quote:
Originally Posted by Zoot
Nice job on the fan controller!
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Thanks!
Quote:
Originally Posted by Zoot
Most fans have some sort of power rating. I think the Akasa ones I had lying around were rated for 100mA at 12V.
If you simply use Ohms law you get an effective resistance of the fan of 12/0.1 = 120 Ohms. Since the fan is just a DC motor, and all motors rotational speed is a function of the current flowing in them. If you assume a linear relationship between fanspeed and current, halve the current and you'll halve the speed.
To do that, just make your resistor 120 Ohms (same as the fan), for 66% fan speed, make it 80 Ohms etc.
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The SP120's quiet are rated @ 0.08 A @ 12 V, which equals to 150 Ohm if my math is correct.
Taking three of them in parallel would yield 50 Ohm for the fans in total. Connecting the
potentiometer (100 Ohm @ max R) in series, that would give you 4 V over the 3 fans and
8 V over the Potentiometer.
I don't know the minimal resistance of the pot though.
Quote:
Originally Posted by Zoot
If you do anything in regards to electronics you'll see it again and again, it comes into everything.
But yes, all you're doing is just limiting the current that the Fan is pulling with the resistor.
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True, the voltage divider is a rather important concept.
Quote:
Originally Posted by JayCobs
Questions:
Is it possible to construct a 12 fan controller similar to what you built for 3? And, would it be cheaper than purchasing one?
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It would be possible. Taking 12 SP120 Quiets in parallel would yield 150 Ohm/12 = 12.5 Ohm
total resistance for the fans without the potentiometer. From there you can take whichever
potentiometer suits best your needs. A 12.5 Ohm potentionmeter would give you 6 V voltage
drop over the fans and 6 V over the resistor, a 25 Ohm pot would give you the same behavior
as in my circuit (provided I haven't made a mistake somewhere, I am admittedly a tad rusty
when it comes to electronics, haven't done anything since last August), meaning 4 V over
the fans and 8 V over the resistor.
What you need to pay attention to is that the potentiometer is specified for the power draw
for your circuit. For example, let's say I have my potentiometer (so, for the circuit with 3 fans)
set at 50 Ohm, meaning I have 6 V over the pot and 6 V over the fans.
Going by each fan having a resistance of 150 Ohm, this would give me a power draw for
each fan of 6 V/150 Ohm = 0.04 A. Since we have three fans, and the entire current for those
three fans needs to pass through our potentiometer, the current through that will be 0.12 A.
This will give us a dissipated power in the resistor of P= 6 V * 0.12 A = 0.72 W. Since the
resistor in my circuit is specified for 4 W (according to caseking's site), this is all good.
As for cost, I think the PCB cost about 4 bucks and the potentiometer another 4 bucks.
Provided you already have a soldering iron it would certainly be cheaper than a prebuilt
controller.
If it would be helpful and desired, I could make a drawing of the circuit, I usually have
an easier time understanding a circuit diagram than a long text describing said circuit
(both together are optimal, of course).
Disclaimer: As mentioned, I'm rather rusty when it comes to electronics. Since
this is rather trivial stuff, I hope I haven't made any errors (that would be rather
embarrassing
), however, Zoot knows this stuff inside out, I'm sure he'll call me out
on any BS.
Update: I will probably have one either tonight or tomorrow, depending on how
well things go. I'm more or less done with the PSU, still need to test it though. Besides
that I'm working on the new back panel and trying to get everything to fit together.
from me! I've thought about counting
Linear Mode
