can i wire 12v pc fans in series?

[aidynphoenix]

I tried it with a pair if identical 80mm fans on a 12v dc adapter and they work, but im not sure if its safe for a PC power supply, or what would be the effective voltage for each fan?

they spun just fine, but they were slower and quieter than they are in series, which was the goal because they are noisy fans.

is this safe?

[Mad_Professor]

Re: can i wire 12v pc fans in series?

you could, but you would be passing more current through the second fan which isn't design to handle no more then itself.

Why not just get a potentiometer? you can wire the fans in parallel and attach it to potentiometer in series then hook it up the the 12v line.

Get a 1k rotary linear potentiometer, wire the supply to the left pin and wire the fans to the center and viola!
Get some heatshrink tubing and a hairdryer and you'll have a nice looking fan controller.
Be sure to add up the amperage of both fans to figure out wattage when selecting a potentiometer.

[Th3_uN1Qu3]

Re: can i wire 12v pc fans in series?

Or just wire them to 7v. Red wire to yellow wire of molex and black wire to red wire of molex.

@ Mad_Professor: Don't you remember Ohm's law? The current stays the same when two devices are in series, it's the voltage that splits between the two.

[ratdude747]

Re: can i wire 12v pc fans in series?

Or just wire them to 7v. Red wire to yellow wire of molex and black wire to red wire of molex.

@ Mad_Professor: Don't you remember Ohm's law? The current stays the same when two devices are in series, it's the voltage that splits between the two.

its not ohm's law. but it is true:

series- voltage changes at each element, current is constant. AKA Kirchoff's Voltage Law.

parallel- voltage is the same at each element, current is different at each element. AKA Kirchoff's Current Law.

[Mad_Professor]

Re: can i wire 12v pc fans in series?

brain fart..

At the time of writing it made sense, now that you remind me, I feel stupid.

Disregard my last post, it's worthless just like me.

[mariushm]

Re: can i wire 12v pc fans in series?

The 7v trick is nice, but it depends on the power supply design when it comes to how many fans you can actually power like that.

I don't remember why exactly but at some point the power supply may turn itself off if you add too many fans and power them like that.

The power consumption of the fans is small enough that you could just use a 0.5-1w resistor to lower then fan's speed. Again, don't remember exactly the value as I did the calculations some time ago, but I think you need about 30-60 ohm.

[aidynphoenix]

Re: can i wire 12v pc fans in series?

thanks guys, i have been looking for a decient fan controller, id like some simple ones that fit a pci slot, but i have 4 fans to control and not 4 free pci slots, looked around for some that filled a cd rom bay, or a floppy bay, and all of them seem to turn the fans off when turned down too far. and also cost about $50. i think id like something more rugged, and relyable. i have concerns about the carbon in pots, burning up over time, i think id like a switch that has resistors for different resistances, that way i can use higher wattage resistors and run multiple fans at once, and not have to worry about them burning up over time. i have been shopping online at, newegg.com tigerdirect, directron, xoxide, and frozencpu. is there any other online retailers that are decient for pc acessories? if i cant find something online, il probably take a pci slot cover, cut out a rectangle in it, and fit a 3 position switch, that will be wired up to different value resistances, one will be low, other will be med, and next will be 12v. no resistance. but that seems like a bit of work.

any suggestions?

[momaka]

Re: can i wire 12v pc fans in series?

The power consumption of the fans is small enough that you could just use a 0.5-1w resistor to lower then fan's speed. Again, don't remember exactly the value as I did the calculations some time ago, but I think you need about 30-60 ohm.

+1
I didn't do any calculations, but I experimented with various resistors before and found that 10 to 60 Ohms usually gives a good range to play around with. At 10 Ohms, the fan will run at nearly full speed and at 50-60 Ohms at low speed. The fans I experimented with were cheap, 80mm sleeve bearing fans rated for 0.12 to 0.18 A of current.
For the higher resistance resistors (40 to 60 Ohm range), you might want to use resistors rated for at least 1W (2W recommended). For the smaller-resistance resistors, 0.5W may be enough, but 1W is recommended.

You can also use a LM317 adjustable voltage regulator to make a variable power supply. With a good heatsink, you can pull up to 1.5A from it. That should be more than enough to power all your fans at once (if you choose to make it that way). Pretty easy to build this circuit too (the LM317 data sheet even tells you how!)

[Scenic]

Re: can i wire 12v pc fans in series?

I'm using a 5.25" bay fan controller by Zalman (ZM-MFC1), mainly because the previous owner managed to create a short and burn a trace off, so I got it for free

They can be picked up pretty cheap, but they need a bit of "fixing" to not be annoying. The LED brightness is controlled via the rpm sense wire of the fan.. so it ends up flickering like mad. putting a 6.3V 1000uF cap in parallel to the LEDs permanently fixes that (and that's exactly what i did to mine.. good use for questionable used caps, in my case old Teapo SC from 2002)

On the other hand, Zalman also made a very cheap manual fan controller called the FanMate II (Newegg link).

It's basically nothing more than a 7805 voltage regulator, a resistor and a potentiometer. That's it.

You could easily build one yourself and put a row of potentiometers onto an empty drive bay cover or something.

I've attached a rather crude "schematic" of how these are wired up internally. The more experienced guys on here would probably want to bash me for how I put this to paper but hey.. I did this who knows how many years ago. Probably before I even registered on here.. lol

[mariushm]

Re: can i wire 12v pc fans in series?

See the third picture on this one:

http://www.newegg.com/Product/Produc...82E16811998065

Can't get much simpler than that... just like the design above.

This one is sort of the same: http://www.newegg.com/Product/Produc...82E16811998808

If someone designs one for 4-6 fans, it would be nice if they made it with an pic or some logic that would turn the fans on sequentially, giving them a bit more juice for a couple of seconds and then lowering them to the previous setting.

Why? If set to 3-5v, some fans may not start but spin once they're started will still spin at such low voltage... and spinning 6 at boot is 3-4 amps on 12v which may matter on 300-400w psus... who wants to adjust fans may try to build a silent machine, with low power psus.

[Scenic]

Re: can i wire 12v pc fans in series?

The Zalman MFC1 I mentioned in my previous post is basically the simple 7805 circuit above times 4, with a rather annoying LED added to each channel.

In fact, most of the affordable 3.5" or 5.25" drive bay controllers use a circuit similar to the one above. Crude but effective.

[ratdude747]

Re: can i wire 12v pc fans in series?

I'm using a 5.25" bay fan controller by Zalman (ZM-MFC1), mainly because the previous owner managed to create a short and burn a trace off, so I got it for free

They can be picked up pretty cheap, but they need a bit of "fixing" to not be annoying. The LED brightness is controlled via the rpm sense wire of the fan.. so it ends up flickering like mad. putting a 6.3V 1000uF cap in parallel to the LEDs permanently fixes that (and that's exactly what i did to mine.. good use for questionable used caps, in my case old Teapo SC from 2002)

On the other hand, Zalman also made a very cheap manual fan controller called the FanMate II (Newegg link).

It's basically nothing more than a 7805 voltage regulator, a resistor and a potentiometer. That's it.

You could easily build one yourself and put a row of potentiometers onto an empty drive bay cover or something.

I've attached a rather crude "schematic" of how these are wired up internally. The more experienced guys on here would probably want to bash me for how I put this to paper but hey.. I did this who knows how many years ago. Probably before I even registered on here.. lol

not bad on the schematic... the only way to make it prettier would be a kicad screenshot (what I do for college lab reports involving schematic drawing and notes involving schematics). but your drawing is pretty enough that it is sufficient (unlike my drawing, which sucks).

[aidynphoenix]

Re: can i wire 12v pc fans in series?

thanks guys, il get some photos on here once i get something that works out. kinda starting to want a fan controler with green led lights, might have to buy something and swap led's. i just want something that looks good, but i also like the idea of it being relyable because i made it myself and wont skimp out on wire/solder/ect.