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  #91  
Old 27-05-13, 07:11 PM
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Mgutierrez33 Mgutierrez33 is offline
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Quote:
Originally Posted by Zoot View Post
Nice job on the fan controller!


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.
Figured that was how you could do it. Been so long since I touched on Ohm's Law... plus I've been delving deeper and deeper into Calculus for my Engineering degree (Computer Engineering) and haven't yet gotten to take my Physics courses to get me refreshed on it (my community college has some terrible scheduling, seemingly put in place to ensure that the students have to stay there for as many semesters as is humanly possible). I studied it heavily though while I was in automotive school, really enjoyed it then and am finally starting to see more applications for it again x-).

But her I am spouting exposition... NEED more of this build to get posted up (but in your own time).

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  #92  
Old 28-05-13, 07:21 AM
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Quote:
Originally Posted by Mgutierrez33 View Post
Figured that was how you could do it. Been so long since I touched on Ohm's Law...
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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  #93  
Old 28-05-13, 09:15 AM
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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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  #94  
Old 28-05-13, 11:20 AM
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alpenwasser alpenwasser is offline
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Quote:
Originally Posted by Zoot View Post
Nice job on the fan controller!
Thanks!

Quote:
Originally Posted by Zoot View Post
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.
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 View Post
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.
True, the voltage divider is a rather important concept.

Quote:
Originally Posted by JayCobs View Post
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?
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.
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  #95  
Old 28-05-13, 05:29 PM
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Zoot Zoot is offline
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Quote:
Originally Posted by alpenwasser View Post
Zoot knows this stuff inside out, I'm sure he'll call me out
on any BS. .
Nah, no need. What you've said is correct.
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  #96  
Old 28-05-13, 06:03 PM
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alpenwasser alpenwasser is offline
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Quote:
Originally Posted by Zoot View Post
Nah, no need. What you've said is correct.
*sigh of relief*

Considering I'm starting a degree in electrical engineering next fall I really should be able to do
this, rusty or not. This is stuff from my high school days.

On another note: I got my first studio light today and have been experimenting around with that.
Unfortunately my camera's batteries have decided to quit after a day of playing around.

I'll give the PSU a good clean and take some proper pictures tomorrow morning along with a
status update for the back panel.

Until then,
-aw
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  #97  
Old 29-05-13, 07:24 AM
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Throbbi Throbbi is offline
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Gotta say, I wasn't familiar with cable lacing and I must look into that for my since I hate cable ties with a passion but i'm forced into used them at present. Looking forward to what else you come up with.

FYI - 1174 holes drilled (no, I wasn't sat with nothing to do before work, honest)
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  #98  
Old 29-05-13, 01:18 PM
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alpenwasser alpenwasser is offline
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Quote:
Originally Posted by Throbbi View Post
Gotta say, I wasn't familiar with cable lacing and I must look into that for my since I hate cable ties with a passion but i'm forced into used them at present. Looking forward to what else you come up with.
It is indeed not something one usually just stumbles upon. Originally I started with a Google
search about "Sewing Cables", which after a little while lead me to cable lacing. It's definitely
not as prevalent these days as it used to be.

Quote:
Originally Posted by Throbbi View Post
FYI - 1174 holes drilled (no, I wasn't sat with nothing to do before work, honest)
Oh dear god, that got an actual, literal from me! I've thought about counting
them, but so far couldn't get myself to do it.

*gives cookie for achievement of the day*

Hm, this gets me thinking: 1174 holes, and for each hole I
  • drilled a small hole for centering (yeah, yeah I know they're not all properly centered ),
  • drilled the actual hole,
  • deburred both sides,

which gives me 1174*4=4696 drilling operations.
No wonder my wrist hurt for two days after I was done.
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  #99  
Old 29-05-13, 02:04 PM
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alpenwasser alpenwasser is offline
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Fan Controller & PSU

Fan Controller - Finished

I've strengthened the fan controller with quite a substantial amount of epoxy glue. It might
not be the prettiest, but it won't be visible and it's pretty much bomb proof at this point.







PSU - Finished (More or Less)

There's still some very minor finishing touches to be applied, but it's as good as done.




24 Pin - Detail

There's a minor mistake in my lacing in the middle lacing section, but I'm not sure if I'm going
to redo the thing just for that. It depends on whether or not it will be visible in the final configuration
when everything is in the case. The lacing is not 100% straight at this point, that will be done
once everything is mounted, there's enough flex to do that.



Fan Cable

This cable will connect to the fan controller, hence only the 12 V wire. Obviously I couldn't
use the same technique for this as for the 24 pin.

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  #100  
Old 29-05-13, 02:17 PM
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hooleee geezus that cabling looks sweet :P the only thing i'm not really liking is the whole bunch of lacing on the 24 pin and on the molex and sata. personally i think it'll look cleaner without them
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