# [5v & 7v & 12v]Creating fan undervolt switches



## TwistedMind

I'm starting a tiny project nothing much. I have set of 4 DPDT switches & waiting on 2 more DPDT switches, some heatshrink tape.

I'm going to stripe an old psu for extra wire. Well what I'm going to do is create three 5v & 7v & 12v on the fly switch sets.

Two switches per application. Six switches all together. Three applications. I'm will be soldering a few leads with terminals onto the switches.

Each set are going to run different fan zones in my case.
#1 will run my fans on my HS.
#2 will run my exhuast fan.
#3 will run four case fans.
Never done this before but I have strong confidence that it will turn out great. This is going to involve a lot of soldering points. I'm looking forward to this. I will be testing the switches with a multimeter & old fans on an old psu with green and black wire jumped on the atx. I am taking precaution before hooking up to main system.

This will be an experience. I will lower the voltages while browsing the net & away from pc, raise em while gaming.
I found a schematic as well.
Here are three photo's + the schematic. I will post the finished project in a few days to a week with photos.


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## TwistedMind

All Finished up.



















Second Set.



















3rd Set. Besides running out of some stuff, had to use different connectors :/. But my soldering has improved from the first set to the third.



















Drilled and mounted the switches to a bay cap.



















12 Volt Selection.










7Volt Selection.










5Volt Selection.


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## ZHoob2004

for getting 7v, it looks like you're planning on connecting the 12v and 5v lines together, correct?

if that's your plan, I would recommend against it because I believe that would also drop the voltage across the entire rail, and raise the 5v rail voltage.

if that's not what you're doing, feel free to ignore my comment.


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## cory1234

Good project, but it seems like a lot of work when you can just pop out the wire with a pen and change it fairly quickly.


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## TwistedMind

Quote:


Originally Posted by *ZHoob2004* 
for getting 7v, it looks like you're planning on connecting the 12v and 5v lines together, correct?

if that's your plan, I would recommend against it because I believe that would also drop the voltage across the entire rail, and raise the 5v rail voltage.

if that's not what you're doing, feel free to ignore my comment.

I did a test after I read your post & finished up creating one 12v 7v 5v switch.

12v with one fan @ 5.074v on the 5v line.
7v with one fan @ 5.078v on the 5v line.
7v with two fans @ 5.082 on the 5v line.
7v with three fans @ 5.086v on the 5v line.
So every fan that you add running @7v increases the 5v line even more by .004v to .005v for each fan, this is with non horse power fans.

If my calculations are correct, if I ran all my fans at 7v, my 5v line will run at 5.109v, I used 7 x .005 = .035 + 5.074 = 5.109v give or take .007v to .014v.

Running quite a lot of fans undervolted @ 7v, this is very bad to do, I am guessing highly not recommended?

Thank you for that important note ZHoob2004.


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## wcdolphin

Nope, your PSU rails have a control system for voltage, within spec, they produce the 'same' voltage regardless of the current.
What you are seeing is a combination of variation in PSU voltage and a variation caused by increased power draw.
You are not changing anything with the 5V or 12V rails of your powersupply!
Voltage is the potential difference between two points.
Thus, in more accurate terms, a molex cable is:
+12V
0V (Ground)
0V (ground)
+5V

The voltage between any two connections is the difference between their potential (with respect to ground (0V), of course)

By Zhoob's logic, by supply any component with 12V, you are making your ground rail increase in potential (which is not the case!)

Further, those measurements are almost certainly within the error tolerances of your digital multi-meter, a variation of 8 mV is very hard to measure!

I do not for-see any problems occuring besides fan damage due to a different rotational velocity, as the bearings and the lubrication system was optimized for some frequency, any variation will cause some increased wear, however I doubt this is even remotely significant.

All the best,
Cory.


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## TwistedMind

Quote:



Originally Posted by *cdolphin*


Nope, your PSU rails have a control system for voltage, within spec, they produce the 'same' voltage regardless of the current.
What you are seeing is a combination of variation in PSU voltage and a variation caused by increased power draw.
You are not changing anything with the 5V or 12V rails of your powersupply!
Voltage is the potential difference between two points.
Thus, in more accurate terms, a molex cable is:
+12V
0V (Ground)
0V (ground)
+5V

The voltage between any two connections is the difference between their potential (with respect to ground (0V), of course)

By Zhoob's logic, by supply any component with 12V, you are making your ground rail increase in potential (which is not the case!)

Further, those measurements are almost certainly within the error tolerances of your digital multi-meter, a variation of 8 mV is very hard to measure!

I do not for-see any problems occuring besides fan damage due to a different rotational velocity, as the bearings and the lubrication system was optimized for some frequency, any variation will cause some increased wear, however I doubt this is even remotely significant.

All the best,
Cory.


Very informative, then I will continue to finish the project.

For the part

Quote:



By Zhoob's logic, by supply any component with 12V, you are making your ground rail increase in potential (which is not the case!)


I'm kinda not understanding. I do have a dvd burner hooked up, don't know if that is considered a component with 12v.

Thank You


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## [email protected]$r1g

U can get 9v by supplying orange 3v & yellow 12v.........


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## TwistedMind

Zomg, my ears are ringing from the silence. I'm loving how peaceful it is. Also, PC sounds like a







Dell







.









7Volt=Dell. 5v seems like the pc is off. 12v while gaming























I also updated Post #2 with finished results.

Quote:



Originally Posted by *[email protected]$r1g*


U can get 9v by supplying orange 3v & yellow 12v.........


I could have, but decided not to a couple days ago.


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## crazyap7

Looks very cool! +rep


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## TwistedMind

Quote:



Originally Posted by *crazyap7*


Looks very cool! +rep


Thanks bud.

I cut off a lot of slack that was not needed as well. Removed those trailer clamps, blue wire connectors, red male female connectors & soldered the wires together then wrapped em with heatshrink. Looks a lot better, whole lot shorter & less bulkier. I didn't grab any photo shots of it yet, one day I will.


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## tha d0ctor

why not just create a parallel type circuit with a dipper switch that each switch has X amount of resistance so by flipping each switch you can add +1v and have a dipper set up with 12 switches ?


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## TwistedMind

Quote:


Originally Posted by *tha d0ctor* 
why not just create a parallel type circuit with a dipper switch that each switch has X amount of resistance so by flipping each switch you can add +1v and have a dipper set up with 12 switches ?

I would not even know where to begin with what your asking.

Got a diagram or create a diagram? I might better understand your suggestion.

Thanks.


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## tha d0ctor

let me conceptionalize something once I get a free moment, hopefully tonight!


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## charliehorse55

You can turn the fans off too, right?

Just flip both switches down and they will have a 0V potential difference.


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## TwistedMind

Quote:


> Originally Posted by *charliehorse55;11541642*
> You can turn the fans off too, right?
> 
> Just flip both switches down and they will have a 0V potential difference.


I just tested it, and yes it shuts em off. I didn't even know that till I read your quote and tried it. Now for it being 0v potential, I dunno, but I thought I read somewhere flipping em that way would ruin something. I guess not though, that's why I never did it till now.

Thanks for that.


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## Liighthead

nice might give this a try sometime









well mostly just for my scyth 3k rpm fan haha loud prick xD


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## mcpetrolhead

I once did something very similar, excpet i used a 3 way switch, this meant i had only one switch per channel.


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## Liighthead

Quote:


> Originally Posted by *mcpetrolhead;12346334*
> I once did something very similar, excpet i used a 3 way switch, this meant i had only one switch per channel.


does 1 have a digagram how that would be setup?


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## mcpetrolhead

umm i cant remember what type of switch i used
i have no idea where it is now, ill have a look at my electronics distribution catalogue if you remind me at some point


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## Liighthead

Quote:



Originally Posted by *mcpetrolhead*


umm i cant remember what type of switch i used
i have no idea where it is now, ill have a look at my electronics distribution catalogue if you remind me at some point










maby i will







if i rember to remind u.
3 way switch.. shouldnt be hard to find :] 
might go have a lookies down the electrions shop if i get a chance.

on 12v
slow 7v?
off nothing? lol


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## mcpetrolhead

yeah 12v was top 7v was middle and down was off, it was a special type of switch which i cannot seem to locate :S


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## daemon123

Sorry to invade your thread,
but here is a simpler way to do it

the 12v and 7v goes as input to pin 1 and 3
the pin2 (common) is sent to postive of fan

and the GND directly goes to the fan


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## mcpetrolhead

Quote:


> Originally Posted by *daemon123;12368200*
> Sorry to invade your thread,
> but here is a simpler way to do it
> 
> the 12v and 7v goes as input to pin 1 and 3
> the pin2 (common) is sent to postive of fan
> 
> and the GND directly goes to the fan


The psu only supplies 12,5,0 on the molex pins. To get 7v to the fan you have to have the + side of the fan on 12v and the -ve side of the fan on 5v.


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## Liighthead

>.< thats the hard part lol

can only get like on/off with that type of switch.. ( faily sure )

as mcpetrol said carnt because u need +12v and +5v to the fan. :]


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## daemon123

aah sorry, i messeg up big time








i will post the one i made for 7v

i made the above kind of one for 12v direct and on 2nd pin was with lm317 controllerd
so up was 12v middle was off and down was the volts i wanted on with the lm317

here is the corrected one

12v + from power directly goes to fan +
5v and GND from power goes to pin 1 and 3
pin (common) goes to GND of fan

so its 12v - off - 7v


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## Liighthead

mmmm not sure.. dont think thatll have "off" though.. just 12v and 7v?

wait for mcpetrol to come







he knows more then me

>.< im confused..


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## TwistedMind

If this helps any of you, this is where I got the diagram and there are a couple more diagrams.

http://www.thebestcasescenario.com/f...ad.php?t=18428


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## mcpetrolhead

Quote:


> Originally Posted by *daemon123;12369232*
> aah sorry, i messeg up big time
> 
> 
> 
> 
> 
> 
> 
> 
> i will post the one i made for 7v
> 
> i made the above kind of one for 12v direct and on 2nd pin was with lm317 controllerd
> so up was 12v middle was off and down was the volts i wanted on with the lm317
> 
> here is the corrected one
> 
> 12v + from power directly goes to fan +
> 5v and GND from power goes to pin 1 and 3
> pin (common) goes to GND of fan
> 
> so its 12v - off - 7v


Yes this would work fine, it just wouldnt have an off position.








I was a bit confused at first because you labeled both the fan wires as positive








Quote:


> Originally Posted by *Liighthead;12369877*
> mmmm not sure.. dont think thatll have "off" though.. just 12v and 7v?
> 
> wait for mcpetrol to come
> 
> 
> 
> 
> 
> 
> 
> he knows more then me
> 
> >.< im confused..


hehehe, caught me just as im going to bed.


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## Liighthead

Quote:



Originally Posted by *mcpetrolhead*


Yes this would work fine, it just wouldnt have an off position.








I was a bit confused at first because you labeled both the fan wires as positive









hehehe, caught me just as im going to bed.










ni nights

would u be our to put a nother ( small? ) switch somewhere along that line so have a on/off? lol

EDIT: so this would work? to switch between 12v and 7v? 
and where would place a on/off switch?







seams alright to have on/off and 12v/7v switch :] still be faily clean ( i guess ) untill work out how to have "off" as well xD


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## daemon123

well the switches i got were 3 postion, up middle and down.

they were cheap chienese


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## mcpetrolhead

a 3 position switch would work fine.


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## Skiivari

dude ***, it looked good until i saw the front panel...
god, why is it so hard to put them in a straight line. Also, why not 3 position switches?


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## TwistedMind

Quote:


> Originally Posted by *Skiivari;12405412*
> dude ***, it looked good until i saw the front panel...
> god, why is it so hard to put them in a straight line. Also, why not 3 position switches?


No need for the three position and two is all i could get "for free".

Well, without a drill press, its hard to keep em in a straight line with it being mesh, bunch of tiny wholes, no real easy way to guide the drill bit drilling free handed.

If you like to try and have a scrap piece of mesh, try it yourself, you'll see.


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## Skiivari

Yeah, sorry for the aggro post, I've got the flu








yeah i understand


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## Liighthead

hey for the 3 way switch one..

is a .up - off - down. type switch alright?







to use.


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## mcpetrolhead

Yeah that would work


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## Liighthead

Quote:


> Originally Posted by *mcpetrolhead;12417476*
> Yeah that would work


might pick up 1 2morro or when i get a chance and try it








this scyth 3k rpm fan gets quite annoying sometimes


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## fshizl

Nice idea!


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## Liighthead

so how would i set it up?
if theirs

UP
OFF
DOWN


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## TwistedMind

Quote:



Originally Posted by *Liighthead*


so how would i set it up?
if theirs

UP
OFF
DOWN











http://www.thebestcasescenario.com/f...ad.php?t=18428


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