Author Topic: how to pull 12v from PSU on PC?  (Read 944 times)

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Offline ddmeltzer8

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how to pull 12v from PSU on PC?
« on: September 30, 2019, 06:55:45 am »
Hello.
Im wanting to pull 12v for
1)fan controller(1-1,5A)
2)LED strip-5630 1 meter
from the PSU.Im completely prepared to cut and solder.I just dont know what wires to cut...

Thanks in advance.
 

Online mariush

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Re: how to pull 12v from PSU on PC?
« Reply #1 on: September 30, 2019, 07:32:19 am »
Molex and SATA connectors have 12v and 5v in them

The lower voltage is towards the center of a device (ex hdd). For sata, you have 3.3v by the SATA data cable, then 5v and 12v on the other side.
For molex, you have 5v on the side with the SATA or IDE data cable, 12v on the other side.





If your psu cables are colored: orange is 3.3v, red is 5v, yellow is 12v, black is ground (com, common) .

You don't have to cut cables. You could just buy a molex to sata  or sata to molex extension cable and cut one of the connectors.

ex molex to 2 x sata :
https://www.newegg.com/p/N82E16812422786?Item=N82E16812422786
https://www.newegg.com/p/N82E16812422643R?Item=N82E16812422643R

sata to molex+floppy : https://www.newegg.com/p/N82E16812422644

So you can just cut one of the connectors and you get your exposed wires.
 
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Offline digsys

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Re: how to pull 12v from PSU on PC?
« Reply #2 on: September 30, 2019, 08:00:58 am »
Quote from: mariush
You don't have to cut cables. You could just buy a molex to sata  or sata to molex extension cable and cut one of the connectors. 
You can pick up all sorts of adapters / converters / dead or cheap P/Supplies from computer swap meets
Hello <tap> <tap> .. is this thing on?
 
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Offline beanflying

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Re: how to pull 12v from PSU on PC?
« Reply #3 on: September 30, 2019, 08:34:14 am »
Way back in the dim dark past I did this hack on an old PSU I had laying around. +-12V rails 3.3 and 5V and a hard switch as it needed one from the motherboard to wake up.

Doesn't get much use now due to much better PSU's but it was handy at the time and still occasionally gets powered up as it is easier than lugging around 10kg of bench supply.

The short answer for the OP is Yellow is +12V and black is ground as shown in the diagram above  :)
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Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #4 on: September 30, 2019, 06:56:21 pm »
Thanks.I think that will do it.
Il post back if theres any issues.

Cheers.
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #5 on: September 30, 2019, 06:58:03 pm »
Oh,i forget.
Does it matter which is 12v and ground on fans?
 

Online mariush

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Re: how to pull 12v from PSU on PC?
« Reply #6 on: September 30, 2019, 08:46:04 pm »
There's only two wires on fan which are 12v and ground. The others are rpm sensor and pwm signal and both are optional.

Pinout is ground, voltage, rpm , pwm tack

See https://allpinouts.org/pinouts/connectors/motherboards/motherboard-cpu-4-pin-fan/
See https://allpinouts.org/pinouts/connectors/motherboards/motherboard-cpu-3-pin-fan-connector/

No it doesn't matter which 12v wire and which GND wire from the PSU gets connected to CPU 12v and GND wires.
 
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Offline MarkF

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Re: how to pull 12v from PSU on PC?
« Reply #7 on: September 30, 2019, 09:35:44 pm »
Oh,i forget.
Does it matter which is 12v and ground on fans?

Yes. 
If you reverse the +12V and GND wires going to the fan, the fan will run backwards.
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #8 on: September 30, 2019, 09:43:35 pm »
But no harm?Does that apply to all DC devices?
Thanks.
 

Offline Monkeh

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Re: how to pull 12v from PSU on PC?
« Reply #9 on: September 30, 2019, 09:48:50 pm »
But no harm?Does that apply to all DC devices?
Thanks.

Not at all. If you reverse polarity on a typical PC fan you will destroy it.
 
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Online mariush

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Re: how to pull 12v from PSU on PC?
« Reply #10 on: September 30, 2019, 09:49:23 pm »
No, MarkF is trolling you.

If you don't connect the fan the right way, there's a high chance you'll damage the fan.

If you don't know which wire is positive voltage and which one is grouns, connect the wire that's supposed to be ground and then carefully touch the voltage wire to your 5v of the power supply.
If you see the fan spin a bit or move a bit, you got the voltage right... so you can connect the 12v wire instead of 5v. 

The reason I suggest 5v is because most fans will tolerate 5v reverse voltage for a second or so (the small time you'd need to see fins try to move)... but may be damaged with 12v.
« Last Edit: September 30, 2019, 10:02:45 pm by mariush »
 
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Offline ejeffrey

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Re: how to pull 12v from PSU on PC?
« Reply #11 on: September 30, 2019, 10:08:42 pm »
Computer fans use brushless motors which means they have a controller and FET switches delivering pulses to the coils.  They will certainly not work with reverse polarity and may be destroyed.

Brushed DC motors have no electronics in them and will generally run backwards if supplied reverse voltage.
 
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Offline JustMeHere

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Re: how to pull 12v from PSU on PC?
« Reply #12 on: September 30, 2019, 11:15:50 pm »
 There should be a 3 or 4 pin fan header on the motherboard.  You should prefer that.
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #13 on: October 01, 2019, 01:58:15 am »
So MarkF was lying?
Thanks.
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #14 on: October 01, 2019, 01:58:50 am »
Monkeh says u r lying!R u?
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #15 on: October 01, 2019, 02:02:01 am »
Thanks.
Is this trolling by MarkF something that is tolerated here?Im quite shocked that no one seems to be offended by this.
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #16 on: October 01, 2019, 02:05:18 am »
NOTE: This message has been deleted by the forum moderator Simon for being against the forum rules and/or at the discretion of the moderator as being in the best interests of the forum community and the nature of the thread.
If you believe this to be in error, please contact the moderator involved.
An optional additional explanation is:
« Last Edit: October 02, 2019, 03:21:38 pm by Simon »
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #17 on: October 01, 2019, 02:08:18 am »
Thanks but im not talking about CPU,but directly from the PSU.(6 pin)
 

Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #18 on: October 01, 2019, 02:13:08 am »
After reading the latest comments and thinking about it,it is quite clear that this forum is not at all what i thought it was!
If people can can just say things that will result in damaged/broken devices without anyone even being bothered by it,im not comfortable taking advice from anyone here.
I hope this will be cleaned up...
 

Offline Monkeh

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Re: how to pull 12v from PSU on PC?
« Reply #19 on: October 01, 2019, 02:18:04 am »
After reading the latest comments and thinking about it,it is quite clear that this forum is not at all what i thought it was!
If people can can just say things that will result in damaged/broken devices without anyone even being bothered by it,im not comfortable taking advice from anyone here.
I hope this will be cleaned up...

You didn't specify the type of fan - there are types which can be reversed and types which cannot. As we're not mind readers, we may make different assumptions.

No matter who gives the advice, do not follow blindly, and realise you're responsible for what you do, not us.
 
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Offline ddmeltzer8

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Re: how to pull 12v from PSU on PC?
« Reply #20 on: October 01, 2019, 02:24:38 am »
So,some PC fans r brushed?That would actually be quite useful.U have any specific fans in mind?

I know im responsible for what i do,if the Eev forum was,i would just keep on using it no matter if it destroyed my devices or not,because u would be responsible.
The thing is that when a poster has several thousands of posts on THIS forum i thought that actually meant something...but if u want this forum just to be perceived as any other random internet forum,im starting to see why no one thinks this is even an issue.
 

Offline Monkeh

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Re: how to pull 12v from PSU on PC?
« Reply #21 on: October 01, 2019, 02:30:35 am »
So,some PC fans r brushed?That would actually be quite useful.U have any specific fans in mind?

Not that I've ever noticed, but you never specified what type of fan. Typical PC fans are brushless, but you still haven't specified what sort of fan you're actually using, so assumptions are being made.

Quote
The thing is that when a poster has several thousands of posts on THIS forum i thought that actually meant something...but if u want this forum just to be perceived as any other random internet forum,im starting to see why no one thinks this is even an issue.

It means they've made a lot of posts. I don't know if he was trolling you or just made an assumption. This is not any other random forum.
 

Offline gnif

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Re: how to pull 12v from PSU on PC?
« Reply #22 on: October 01, 2019, 03:02:48 am »
So MarkF was lying?
Thanks.

No, he was not, you did not specify that it was a computer fan, he may not have much experience with computers and as such assumed you were using a brushed DC fan, which can be reversed by switching the polarity.

Monkeh says u r lying!R u?
Thanks.
Is this trolling by MarkF something that is tolerated here?Im quite shocked that no one seems to be offended by this.
And u should stop telling others what they should prefer!Idiot.
Thanks but im not talking about CPU,but directly from the PSU.(6 pin)
After reading the latest comments and thinking about it,it is quite clear that this forum is not at all what i thought it was!
If people can can just say things that will result in damaged/broken devices without anyone even being bothered by it,im not comfortable taking advice from anyone here.
I hope this will be cleaned up...

This barrage of messages was over a 14 minute period, this is NOT live chat, you have to give people a chance to respond to your questions. Nobody was offended at @MarkF, but I am sure many, including myself, are offended by your impatience and name-calling. This forum is full of patient and mature people very willing to teach and IMO is one of the most friendly places on the internet. Don't let my admin status fool you, this is not my forum, I am simply a forum member what helps Dave with server management, which I do out of my own pocket and time because this community gives so much to people like me that want to learn.

Also on the actual topic, a brushed fan (ie reversible) would be a bad thing to use inside your PC if that's your intention. Not only will noise be a concern due to no speed limiting, but electrical noise would be a concern also, the arcing of the brushes on the commutator as it switches coils emit EMI, which could interfere with the operation of your computer. The DC motor would also introduce noise in the forum of high voltage spikes as the magnetic field of each coil collapses unless you add some protection (usually a snubber diode), and as the brushes wear (they literally grind down) fine conductive carbon/copper particles would be thrown into your PC case and could cause shorts over time. Also, a brushed motor wears out far faster and uses more energy.

There is a reason why we use brushless fans in computers.

If you really want a reversible brushless fan I suggest you look at building or obtaining a brushless motor controller and replacing the electronics of a brushless fan with your custom controller, though I believe that this is a bit beyond your abilities at this time based on this and your other threads. Otherwise, it might just be easier to mount two fans back to back and only power up the one you want based on direction of airflow.
« Last Edit: October 01, 2019, 03:35:23 am by gnif »
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Online Ian.M

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Re: how to pull 12v from PSU on PC?
« Reply #23 on: October 01, 2019, 03:55:19 am »
Also, a typical PC PSU may well be able to deliver 30A at +12V.  Make a mistake with your connections, and if you didn't include an inline fuse, odds are you'll burn something.  If what you burn is the PSU output cable you tapped into, it may melt through the insulation on a 5V or 3.3V wire where the bundle comes out of the PSU, and that can dump 12V onto the 3.3V or 5V supply, which will probably fry your motherboard.  Worst case, it could fry your motherboard, CPU, RAM, and all add-in cards and drives.  If you are really unlucky, the dead parts can then kill whatever you try to test them in!

Therefore PC modding should *NOT* be attempted by anyone who doesn't have plenty of patience, and a good understanding of electrical theory and safe wiring practices.  Also, don't attempt to mod your main PC unless you've got a full backup + a spare that can get you back on the internet!
« Last Edit: October 01, 2019, 03:58:55 am by Ian.M »
 

Offline JustMeHere

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Re: how to pull 12v from PSU on PC?
« Reply #24 on: October 01, 2019, 05:01:19 am »
And u should stop telling others what they should prefer!Idiot.

I was hoping you could do a little research on your own, but I will give you the answer:

The advantage of using the chassis fan header on the motherboard is that system can monitor the fan for health (3-pin header) and control the speed (4-pin header).   Some motherboards will control the fan speed via the 3-pin header.
« Last Edit: October 01, 2019, 05:08:30 am by JustMeHere »
 


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