How to Wire a 12V Case Fan to a Molex PSU Connector With an Inline Switch?

Hi!
(Please note I am a complete noobie, so if you get technical it will probably fly over my head, today is the * first day* I have started "playing" with my own circuits.

I want to add a switch to my computer that starts and stops my 12v cooling case fan.
So basically:
Take power from PSU via Molex male
output power to fan via Molex female.
Please have a look at the attached file and tell me if I got it right.
(This is the switch if you are interested: http://www.ebay.co.uk/itm/360536153036?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)
Thanks!
Ryan

Ryan,

The wiring scheme looks good, so long as you can be sure that yellow is +12 VDC and black is your reference node ("COM", "ground", what have you). Do you have a multi meter to check the voltages with? That's a must have for electrical DIYers.

Also, depending on your PSU, I would consider fusing the fan. Check to see if the output of the PSU offers any sort of circuit protection, and evaluate your options from there.

-Cody

Hey Cody!

Thanks for replying!

Didnt know it was also called "COM", only heard of "ground" so far, already learned something new :)

I have an old multimeter that I used to check if AA batteries were dead or not, I wonder if I can use that or I have to get a new one...(?)

> I would consider fusing the fan.

What does that mean? (Sorry, am a noob)

> Check to see if the output of the PSU offers any sort of circuit protection

Will this be written on the PSU box or something?

Thanks!
R

well technically if all you want to o is switch the +12 (hot = yellow) sure that will do the job. I won't get into the whys, etc, etc, etc. Electrically it will work. This is simplistic. There are two more little goodies that you will need to add to your circuit and I will not explain why. I'll just give you a marked up schematic.

Some other strange things could happen because of the transient load you will put on the +12V, like an audio noise, pop, click or even a video glitch. It could you'll just have to see. If it does, then that's fixable, pretty easy.

I'll send you the MKUP schematic shortly.

Thanks!

This was bugging me for a while so I made it my first ever own "project".

Basically, I want to put 3 fans on when I am doing some video rendering and my comp is overclocked to 4.4ghz, otherwise put off the fans when its underclocked at 2ghz.

Once I get this working, I can start going through the other pages of "Electronics for dummies"

Ryan,

Always happy to help, I'm still a pretty big newvb myself :)

COM is not _exactly_ interchangeable with GND, I didn't mean to give that impression. COM is usually used as a reference node for systems where there are a lot of different power supplies, and where they aren't all necessarily referenced to the same point. For instance: the reference terminal of a 24 VDC power supply could be called "24VDC COM" for clarity sake. These usually are referenced to ground in some fashion, but the added clarity helps manufacturing techs sort things out in large complicated systems.

Any old meter should work. Set it to DC voltage mode, and measure between the yellow and black wires with the PSU on. It shuld read positive 12 volts.

By "fusing the fan" I mean putting a fuse in line with it. I know you had one in the schamitic from the other thread you posted today, it is a very good idea. It will make sure that nothing is damaged if something in your circuit happens to short out, Tesla forbid.

The PSU should have some sort of manual that tells you if the output is already fused. If it is, don't sweat putting one of your own in.

I really have to say one thing, this forum has some really decent folk!

I expected quite a bit of flack as I am such a noobie, but 99% of the people who replied have been so friendly and giving,* thanks again guys!*

I have been on quite a few computer programming forums where a lot of people are total ******s and answer noobs with a "RTFM" instead of a simple link...

You 'electronics guys' are cool in my book

Ah!
That clears quite a bit up ;)

About the schematic, I didnt make that, got it from Google images :p and was one of the few that I did understand so copied and pasted it, but thanks to you I have a better understanding of that schematic as well!

diode is reverse mmf protection, cap protects switch arching and frying. not special parts, radio shack stuff.

Well if you are truly a dummy, skip going through the other pages of Electronics for dummies. Besides nobody does that, not really.

What would happen is you would burn the fan and switch up, then you would read, that is the preferred approach for all of us, even rocket scientist!

Thanks!

Would love to skip it as I dont really like the dummy books but I thought I would go through the first few chapters as right now I know next to nothing... just a hair above completely nothing and didnt know which site / book / video to turn to to learn the _basics_ of electronics.

Always had a desire to learn, I'm a computer programmer by profession, but never really knew where to start so now I just said "screw it,i'm gonna do something" and bought a few things off ebay and... well, these are the 2 threads that came off it :)

quite happy I took the step, in all you guys seasoned eyes it might not be much but for day one to see something light up, that I put together... feels fantastic!

Can you explain what is a "reverse mmf protection" or give me a link please? Google is not helping

Those connections don't look right. The terminal on the switch that the black wire connects to looks like it might be the "pole" and the yellow wires might be the two "throws" of a Single-Pole_Double-Throw switch.

Do you have a multimeter? If so, check for continuity between each of the terminals. Do this twice, once with the switch flipped one way and again with it flipped the other way.

Case 1: If the terminals with the yellow wires connected show "closed" with the switch flipped one way and "open" with it flipped the other way, then that's half way to being correct.

Case 2: Next check to see if there is ever continuity between the terminal with the black wire connected, and the terminal with the yellow wire that goes back to the power supply (not the one that goes to the fans) [again with the switch flipped one way and then the other]. If there is, then remove the black wire, because you will short out the power supply in one of the switch positions. Otherwise it should be OK, unless...

Case 3: If the switch has three positions, then this becomes a bit more complex.. Just follow this rule: if any of the switch positions cause continuity between the terminal with the black wire on it, and the terminal with the yellow wire that comes from the power supply, then it is wired incorrectly. Also, if there is no case where one switch position connects the two yellow wires and another switch position opens the two yellow wires, then the wiring is incorrect.

So, find two terminals that are open in one position of the "bat" and closed in another position of the bat and connect the yellow wires to those terminals. The black wire doesn't even need to be connected to the switch, and in fact, I would recommend NOT connecting it.

BTW: when checking continuity, make sure your switch assembly is disconnected from the power supply

I didn't see the reference to the eBay site where you purchased this switch. I don't see a hook-up diagram or any information regarding what the terminals are, but it looks like it's a SPST on-off switch with an LED. But beyond that, I have no idea how to hook up that switch. Did it come with a diagram or other info for how to connect it?

Also called Revers EMF. MMF is MagnoMotive Force and EMF is ElectroMotive Force. This occurs when switching power to anything that has an inductor (or coil). The explanation is a bit involved, but I wager that it will be covered in your "Dummy" book.

I believe what Earl meant to say is "reverse EMF."

The short version is this:

Fans are run off of an electric motor, which usually involves one or more current coils. These coils have the primary desired effect of creating a magnetic field and turning the motor's rotor.

They also have a (usually) undesired secondary effect of behaving like inductors. Inductors oppose changes in current. Any time a change in current occures through an inductor, the inductor creates a large voltage to oppose the change. When people want to sound really smart, they sometimes refer to this large opposing voltage as a "reverse emf" or "reverse electro-motive force."

In the case of large inrushes of current through major inductors, this "reverse emf" can shorten the life of many different types of components. Switches, relays, and capacitors are common victims. The diode helps this problem by "turning on" when there is a reverse voltage across the motor, shunting the voltage and preventing damage. Coloquially, we call this a "Flyback diode" or a "Supressor diode"

Further reading, if you're interested:
-Reverse EMF
-Motor protection
-Induction
-Flyback Diode

Personally, in the case of a 12VDC fan, I would not be too inclined to worry about the diode and the cap. But that's just me, use your own discretion in all things

Hi Ryan,
By taking a bit of time to read up on the basics, you will progressively gain knowledge and ideas of what is possible, and soon be able to design and make circuits work (almost) the first time.
(Just like we all do (sometimes). ;-)

To obtain an understanding of electronics, the following sites offer free courses of instruction and advice for beginners. Have look at a few, and discover which one(s) suit your approach. Start with simple projects and work your way up. We will always be here to offer the best advice and wisdom we can.

Old (allegedly Chinese) proverb: “A journey of a thousand miles begins with but a single step.”

www.learnabout-electronics.org/index.php - Descriptions of components and principles, good diagrams, animations, & fault-finding techniques

http://www.satcure-focus.com/hobby/index.htm - Useful range of ideas tutorials circuits links etc

http://www.allaboutcircuits.com - a series of online textbooks covering electricity and electronics

http://electronics-for-beginners.com/links.php

http://www.hobby-hour.com/electronics/ - Teaching from basic principles, resistor code calculators, projects

http://www.radio-electronics.com - useful information and tutorials

http://www.electronics-tutorials.ws/index.html - plus calculators & tools

"Personally, in the case of a 12VDC fan, I would not be too inclined to worry about the diode and the cap. But that’s just me, use your own discretion in all things ."

This could be true. We don't have the fan specs or the switch specs. Also most DC fans already have the inductive MMF diode protection in the design anyway, to improve the reliability of the electronics. As for the switch, it would be good to put the cap in because you don't have test results to show it isn't necessary. I can not imaging a switched inductor design that doesn't use voltage snubbing across the switch.

Hey,
Thanks for replying (and sorry for my late reply, was away)

It is indeed a SPST on-off switch (found that detail on another sellers page) and it didnt come with a diagram.

Will also follow your above advise about checking with a multimeter ;)

Cheers/thanks!

Thanks Steve, Cody, Earl!
(...and sorry for my late reply, was away)

Hey,
Thanks for replying (and sorry for my late reply, was away)

Oh man! Lucky I dont have a limit on "thank yous" or I would have run out on this post :)

thanks for all the info x 10, should keep me busy for quite a while!

Cheers guys!