Greetings PCA'ers! I've got an upcoming mod planned, but since it's not a full-blown project, I just decided to document the mod in this log.

The 411:
I bought a 6 channel fan controller from Frozencpu.com around Christmas time this past year. The controller has six, 3 position switches, where you can select fast, slow, or off modes. The controller itself runs great... but I've noticed it will often cause my computer to restart or shutdown only when switching from high to low speeds. I assume that when the controller switches from a high fan speed to a low one, the controller dumps the extra current back into the system, which is when the PSU freaks due to it's tight current in-rush tolerences.


Solution:
I've thought about just buying another fan controller and being done with it, but I love the way this controller works... and you can wire the fans directly to the controller without the need for any kind of 2 or 3-prong plug. I've decided to canabalize a small 160W generic PSU to serve as a secondary dedicated PSU for the fan controller only. I've tested the controller with this 160W PSU to see how it behaves, and cannot for the life of me get the PSU to fail... so I think it'll work.


A convenient thing I found about this little PSU is that is is almost the same width and height of a pair of CD drives stacked on top of each other, so I plan to cram this 160W psu into the lower two drive bays of my case, underneath the existing cd drives.


To get power to the secondary PSU, I'll have to relocate the 3-prong 115V power plug in the PSU to the back of the case where it will be more accessable.


I've also already removed unecessary wires, like extra molex connectors and the mobo power cable... everything except one molex rail and the green and black leads which are needed to manually jump the PSU.


I won't actually be starting this mod until later in the summer, as I'm currently waiting for a new LCD screen for my laptop. After I fix that, I'll be able to start on this mod. In the meantime, I was hoping some peeps could chime in and offer tips, suggestions, or whatever.

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Jobistober looking forward to see how it turns out for you, good luck to you on your new project.

That is a good idea! I have the same problem on one of my machines when I turn the cold cathodes off (got 6 of them)

+Rep just for having such a good idea

wow jobi this sounds like a intersting mod ill keep checking on this one also thanks for the awesome sig

Super idea jobi,but I was wondering about use of only 1 voltage line on psu.I`ve read over and again something about all lines need to have a load in order to operate stable.Other wise Thumby Up,Jo

Quote: Originally Posted by jofultner Super idea jobi,but I was wondering about use of only 1 voltage line on psu.I`ve read over and again something about all lines need to have a load in order to operate stable.Other wise Thumby Up,Jo

Well, I won't say you're wrong... cuz I honestly don't know. But I'd suspect that's only with newer power supplies. While I was working on this little 160W, I noticed the red, yellow, and ground leads of both rails of the PSU are soldered to the same places... and I only have one component load to run, so it doesn't really matter in this case.

I do know that it's important to adequately load the 5V rails to get a stable 12V. I appreciate the concern, but it's just an old PSU powering some fans... not really life or death.

BTW-
I have a question for you guys. Should I wire the green and black jumper leads to a manual switch, or a relay running off my primary 500W PSU? I kinda want the convenience of a manual switch, but want to see what you all have to say.

I would personally go with a relay as i wouldnt want to forget to turn my fans on one time. But thats just me - i can be awful forgetful at times... like going into a game session only to crash out because i forgot to turn my CPU and GPU fans from min to max... DOH!

Being able to control everything is great but i prefer automated control where ever possible.

Nice idea though I'm sure either way would work just as well! +rep heading your way!


Mark

I would try and go with automated too. I too can forget thing easily and it would just make things easier.

Be sure to show us the diagram you used to wire the second ps from the primary psu in order to run stable.I do like this idea,on my muskateer or aerogate.Was only wondering about that load situation thingy.Jo

Ok guys, so I'm gonna go with a relay to power up the secondary PSU with the primary. I'll take a trip to radioshack and find the smallest relay possible. I know how I'm gonna do it, but I'm going to wait until I have pics to show... you guys are going to love it! Don't you just love surprises?!?!

I'll also be sure to provide a diagram for you schematic readers to enjoy

oooo diagram my favorite !!!!
jobi can you recall how much you payed for that bad boy the fan controller

Quote: Originally Posted by project vegas oooo diagram my favorite !!!! jobi can you recall how much you payed for that bad boy the fan controller

FrozenCPU Dual Voltage 6 Port Baybus $28.99
LINKY

Quote: Originally Posted by THRASHER2 6 Port BayBus - $18.95

Lol, they don't call you the Deal Dude for nothin'

OK lets see if someone can get it 10.00 cheaper than that,lol.Jo

Quote: Originally Posted by THRASHER2 6 Port BayBus - $18.95

this is a great idea i cant wait to see how it turns out

this is a great idea! i have been wanting to do something like this but couldn't figure out how to cram another PSU into my mid-tower.

have you considdered...or maybe i should first ask: would there be a way to keep the fans running for 5 or 10 minutes after shutdown?

Quote: Originally Posted by BigJunk93YJ this is a great idea! i have been wanting to do something like this but couldn't figure out how to cram another PSU into my mid-tower. have you considdered...or maybe i should first ask: would there be a way to keep the fans running for 5 or 10 minutes after shutdown?

Well, I don't know why you'd want to do something like that... not to say it couldn't be done though. You'd need some kind of timer mechanism that is activated by shutting down your primary PSU and starts a timer.

i dunno, i have seen these things that keep the fans going for a short time after you shut the system down based on the idea that your heatsinks and whatnot are going to give off heat after the system shuts down. i know it probably isn't necessary but i was just wondering. could do the same thing with a w/c setup too: keep the pump and rad fans going for a couple minutes after shutdown to remove the heat stored in the parts you are trying to cool and the w/c system itself.

but anyway, can't wait to see how it comes out.

You would need to use a capacitor.

If the capacitor was placed in parallel to the supply to the fanbus then it would be charged to the supply voltage and then once the PSU is turned off discharge through the fanbus, keeping the fans on.

+12V-------------------
............|....................|
...........---..................R (R = Fanbus)
...........---..................R
............|....................|
GND--------------------


As for the capacitor required... well - here we go!

the discharge time for a capacitor is based on its time constant.

The time constant for a capacitor is the time it takes for the capacitor to charge / discharge to 63% of its final value... ie if it were charging from 0-100V then the time constant would be the time to charge to 63V.

The time constant T = RC, where R is the resistance in the circuit and C is the capacitance of the capacitor

Another important formula in this problem is the 'Universal Time Constant Formula' (UTCF)

V(t) = V(0)*(e^(-t/T) )

Not very clear but hopefully you can see what it is supposed to look like.

SO... where does this leave us??

Well...

Take an average fan, assume a 0.5A pull at 12V. Using V=IR that gives a resistance of approx 24ohms (24R)

Now assume that the fanbus places all those fans in series and assuming you are keeping them at maximum flow, ie 6 x 24R fans in series that gives a discharge resistance of 1/R = 6* 1/24 = 4R

SO... our time constant now becomes 4C (the value of our capacitor is still unknown)

Going back to the UTCF;

V(t) = V(0)*(e^(-t/T) )

Where; V(t) = 0.1, V(0) = 12, t = 10 minutes = 600s, T = 4C

V(t) is not taken right down to zero as this makes the calculations more or less fade to nothing! lol

We get;

0.1 = 12 * (e^(-600/4C) )

=> 0.1/ 12 = e^(-150/C)

=> -150 / C = ln(0.1/12)

=> -150 / C = -4.787

=> C = 150 / 4.787

=> C = 31F


Things to note:

1) I may very well have gotten something wrong here as i am pretty tired and dont REALLY remember my capacitor theory as well as i should do...

2) 31F is RIDICULOUSLY high! i mean UBER high! - this is why i think i may have gone slightly astray in my calculations... i mean... capacitors are usually measured in MICRO farads... not entire farads... and ESPECIALLY not tens of farads! lol

Thats said though - a discharge time of 10 minutes across only 4 effective ohms of resistance is quite a big feat...

eg - 5 mins, 6 x 24R fans, 12 V becomes 15F

2.5 mins, 6 x 24R fans, 12 V becomes 7.5F and now we are starting to talk about high, but more do-able numbers...

And if you can assume that the resistance of each fan is increased by the fan bus (slowing it down) then the capacitance in turn will decrease...



As i have said... dont trust my calculations entirely... there may well be something i am missing that is blindingly obvious... Nerdz? this your territory at all? lol

Anyway - thats me done!


Enjoy


Mark