how to pull 12v from PSU on PC? - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: September 30, 2019, 06:55:45 am
content: Hello.Im wanting to pull 12v for1)fan controller(1-1,5A)2)LED strip-5630 1 meterfrom the PSU.Im completely prepared to cut and solder.I just dont know what wires to cut...Thanks in advance.

author: mariush
author_rank: Super Contributor
timestamp: September 30, 2019, 07:32:19 am
content: Molex and SATA connectors have 12v and 5v in themThe 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=N82E16812422786https://www.newegg.com/p/N82E16812422643R?Item=N82E16812422643Rsata to molex+floppy :https://www.newegg.com/p/N82E16812422644So you can just cut one of the connectors and you get your exposed wires.

author: digsys
author_rank: Unknown
timestamp: September 30, 2019, 08:00:58 am
content: Quote from: mariushYou can pick up all sorts of adapters / converters / dead or cheap P/Supplies from computer swap meets

author: beanflying
author_rank: Super Contributor
timestamp: September 30, 2019, 08:34:14 am
content: 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

author: mariush
author_rank: Super Contributor
timestamp: September 30, 2019, 08:46:04 pm
content: 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 tackSeehttps://allpinouts.org/pinouts/connectors/motherboards/motherboard-cpu-4-pin-fan/Seehttps://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.

author: MarkF
author_rank: Super Contributor
timestamp: September 30, 2019, 09:35:44 pm
content: Quote from: ddmeltzer8 on September 30, 2019, 06:58:03 pmYes.If you reverse the +12V and GND wires going to the fan, the fan will run backwards.

author: Monkeh
author_rank: Super Contributor
timestamp: September 30, 2019, 09:48:50 pm
content: Quote from: ddmeltzer8 on September 30, 2019, 09:43:35 pmNot at all. If you reverse polarity on a typical PC fan you will destroy it.

author: mariush
author_rank: Super Contributor
timestamp: September 30, 2019, 09:49:23 pm
content: 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.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 30, 2019, 10:08:42 pm
content: 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.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: September 30, 2019, 11:15:50 pm
content: There should be a 3 or 4 pin fan header on the motherboard. You should prefer that.

author: Monkeh
author_rank: Super Contributor
timestamp: October 01, 2019, 02:18:04 am
content: Quote from: ddmeltzer8 on October 01, 2019, 02:13:08 amYou 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.

author: Monkeh
author_rank: Super Contributor
timestamp: October 01, 2019, 02:30:35 am
content: Quote from: ddmeltzer8 on October 01, 2019, 02:24:38 amNot 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.QuoteIt 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.

author: gnif
author_rank: Unknown
timestamp: October 01, 2019, 03:02:48 am
content: Quote from: ddmeltzer8 on October 01, 2019, 01:58:15 amNo, 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.Quote from: ddmeltzer8 on October 01, 2019, 01:58:50 amQuote from: ddmeltzer8 on October 01, 2019, 02:02:01 amQuote from: ddmeltzer8 on October 01, 2019, 02:05:18 amQuote from: ddmeltzer8 on October 01, 2019, 02:08:18 amQuote from: ddmeltzer8 on October 01, 2019, 02:13:08 amThis barrage of messages was over a14 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.

author: Ian.M
author_rank: Super Contributor
timestamp: October 01, 2019, 03:55:19 am
content: 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!

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 01, 2019, 05:01:19 am
content: Quote from: ddmeltzer8 on October 01, 2019, 02:05:18 amI 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.

author: Simon
author_rank: Unknown
timestamp: October 02, 2019, 03:22:52 pm
content: Quote from: ddmeltzer8 on October 01, 2019, 02:13:08 amPerhaps you should learn some patience and get some experience. This is not a paid for Q&A, people give up their time to help each other and not everyone is an expert.