Fan Speed Controller Q?

hey all

my DVD player was overheating so i put in a couple 50mm case fans and the top of the thing stays cold now. so that worked great, but the problem is, it sounds like a vacuum cleaner. guess its time to add a fan speed controller.

i have one of the ones from a thermaltake volcano 11 that goes in a PCI slot. the problem is it has some form of plug that is not a normal fan header, and so i dont know exactly what to do. basicaly the controller has a black cable and a red cable. they both go to one of the two pins in the plug. thats it.

do you think it would work to splice just rip that plug off, then cut the 12v line to the fans, and connect red to one end of the cut and the black to the other? heres a pic of what im thinking ===> [/IMG]

I'm not gonna be calling myself an expert or anything (after all, I turn to here for help ).

That speed controller is usually pluged into another plug on the thermaltake fans. I have a SF2 (mistake... ), and use one of those. I am not quiet sure how the circuitry works, but I think the knob does not have all the amps the fan pulls go through it. For that reason, I think you should not use it how you drew it out; it might burn the controller up.

On the other hand, I know several posters here know how to wire a rheostat (or something) that will acomplish what you want. That will give several steps for your speed, but IMO is alot to solder up.....

If I were you, I would simply get a couple resistors (maybe 100 ohm??), and start from there. BTW, the resistors probably cant handle the amps either, so you will have to wire them in parrallel, which lowers their ohms (2 100 ohm = 1 50 ohm). But to get it back up, just throw several of those together to get a series. BTW, I think you may need to get like 3 or 4 of the common 1/4 watt resistors in parrallel so they dont burn out.


If anyone sees any mistakes in my post, please feel free to clear it up.

That brings up some interesting quandries. i never concidered this thing not being able to handle the power. i purposely opted to not use resistors as i would like to be able to make adjustments for warmer days or what not, as i live in an area that is like 4000 degrees in the summer and like -4000 in the winter.

Oh hey, Reno.... Might get a tad bit warm.... You could always be cheap like me and make a switch to switch between two volts.

ok, i tried that fan speed controller idea... it didnt work. the fans were either on or off with it. so now i guess i concider the resistor idea... the problem is, i know NOTHING about this stuff. anyone care to give me a 101 or something? what do i need to know, what should i use, and can i get them at radio shack? lol.

K, hold on for the ride

Basics (as I understand them)
ohm = the amount of resistance. Ohms Law says Resistance = Voltage / Current. Resustance is messured in ohms, voltage in volts, and current in amps.

A simple example is for LEDs. Say a LED drew 20 ma, and 3 volts. You power source is a 12 volt line. Find the voltage (the difference of source and load) 12 - 3 = 9. Then divide that by the current (make sure its in amps, not milliamps) 9/0.02 to get 450 ohms.


Unfortunatly, fans are not the same deal... I was trying to figure out how to wire a LED on/off switch and a fan 12/7v switch, and this is the thread I found helpful. Big note: FANS ARE NOT LIKE LEDs.

Somethings important from that thread:
http://www.cpemma.co.uk/sdiodes.html (Diodebus, varible voltage).

If you plan to go with the resistor with switch plan, you will connect it something like this:
That has just one fan in the picture, just wire the other one in parrallel.

We also determined that a 12 volt, .17 amp fan would require about a 46 ohm resistor to 'be on 7 volts'.

Another thing to look for is that the fan described above would require a resistor that could handle at least 1/2 a watt. I know radioshack has a 2 pack of 10 watt resistors for like a buck (just to be on the safe side )

A QUICK guess for what ohm resistor you need might be about 70 ohms... VERY QUICK guess. To be more accurate, you could try plug the specs of your 50 mm fans into klath's formulas.

thanks man.
that is very helpful. that and a quick readthrough of http://www.pcreview.co.uk/articlelist-48.php helped a lot too. (incomplete unfortunately)

ya know, when i was a kid my dad got me one of them cool circuit boards with the springs all over, and you connect them with wires, just like the book tells you to. i loved doing that and he alwasy told me i should read and learn the section that explains it all, but i never did. so a shoutout to my dad *I shoulda listened to ya!* lol.

well, i am at a point where i want to learn this stuff, and i need to learn this stuff, so im going to have to take some time to do some serious research. im just gonna have to squeeze it in when i have time, so who knows how long it will all take

my fans are 12v and 0.12A, so if yall wanna tell me exactly what resistors to buy, that wouldn't hurt so i can get this up and running again. i have spliced a 12V and a ground into the wire coming straight off the players power supply, the wires run a few inches and then i spliced the two fans together, and i think it would work best to have the resistors between the two Y splices (like where i showed the fan speed controller splicing in earlier) right?

wiring diagram (had to draw it out, i cant picture what you are saying, and give you something to compare to... ):


I of fan at 12V = power/12V
I = 1.44/12
I = 0.12
Rfan = Power/I^2
Rfan = 1.44/0.12^2
Rfan = 100
Vfan = (Rfan/(Rfan + Ra))*12
7 = (100/(100 + X))*12
.583 = 100/(100 + X)
(100 + X)(.583) = 100
100 + X = 100/.583
100 + X = 171.53
X = 71

My estimate was close.... too close... that scares me.

Anyways, that is with one fan....

I of fans at 12V = power/12V
I = 2.88/12
I = 0.24
Rfan = Power/I^2
Rfan = 2.88/0.24^2
Rfan = 50
Vfan = (Rfan/(Rfan + Ra))*12
7 = (50/(50 + X))*12
.583 = 50/(50 + X)
(50 + X)(.583) = 50
50 + X = 50/.583
50 + X = 85.76
X = 35.76

Hmm.... I thought u would need to double it, but instead its half... That doesnt make sence for me.... But I guess have someone check it, or you could try wire 4 of these in parrallel to get a 37.5 ohm, 2 watt resistor or http://www.radioshack.com/product.a...11_002_014_002&product_id=271-1108]3 of these to make a 33 ohm, 1.5 watt resistor... BUT I AM NOT TOO SURE. I would say PM someone knowlageable from the other thread, such as klath, because I am not too sure... Unless u want to try it, and keep a eye on the resistors to make sure they dont burn up.

It would be alot easier to get about a 100ohm pot and use that instead of resistors. A pot is a variable resistor and will let you adjust the fans on the fly.

12v-----------<pot>------<fan>--------Ground

The 100ohm is a guess as I havent done to math yet.

Heh Neonblingblig, I see you remembered a lot of the stuff I posted in your thread. For Neon's switch, it made more sense to have static resistors rather than pots.

For your case, I would get a pot and stick it where you have the speed controller. Since the pot would be handling double current of one fan, I would make sure it can handle that much otherwise your pot might be smoking. I burned plenty of pots before when lowering the resistance too low.

I doubt a regular pot will handle the current from those two 50mm's if they are fast enough to sound like vacuum cleaners. The other route you can go is get a SPDT switch. Thats basicly a 2-way switch with 3 leads. Wire the center up to the black wire on your fans, then one of the outer wires to the black ground wire from a molex, then the other side to the red +5v line from a molex. When it's on the black ground side, the fans will get 12v. On the other side they'll get 7v.

thats a thought, but being as this is a dvd player, i dont have molex connectors to work with, and i dont know for sure if there are +5v lines in there or not.. ill have to i check when i get home. how does that get to 7v though? i dont get that concept.

HiProfile has the right idea, I will just detail it.

There is a much easier way to do this w/o resistors. Get a three position switch on|off|on connect 12 volt one in, one out. On the other side(This is the kicker) take a 12 volt and 5 Volt connect(twist) them together on the input side of the other "ON" side and a single wire output this will make this line 7 volts. Then just connect both the 12 and the new 7 volt line to the hot wire of the fan and a common ground. This is the simplest way to make a 12|off|7 switch. So basicly it would work like this... "ON" right would feed 12V, Center "OFF", "ON" Left would feed 7V.

I hope this is clear.

S...12V + 5V <--In
W..-------------------out 7V__
I..........................................._
T..........................................--Fan Positive+___"FAN"____- Common Ground
C..--------------------out 12V_
H..12V <--In

Oh, the 12v to 5v mod. I just assumed DVD players never had a 5V line -_-. SOOOOOOOOO much easier. Or a 12v/5v switch...

All I understand about the 7v concept is that the difference in the voltage. For example, on the 5v line on a computer, there is 5 volts different between the red wire, and the negative (0v) wire. So, the difference between 12 and 5 is 7.... ta da.

Before I go into detail about wiring and switches and stuff, can you do it in your dvd player?