How to run 6 fans on one rheostat?

[RIG RIDER]

I have 6 120mm fans that draw .42A each and I need to control the rpm of all 6 at once.
I don't know how to wire the rheostat nor do I know what rheostat to use.
Some help from the members here would be great.
This is what I need to tame. *click pic for a bigger pic*
http://img235.imageshack.us/img235/6434/dscf1897hx8.th.jpg (http://img235.imageshack.us/my.php?image=dscf1897hx8.jpg)

[gangaskan]

eeek!!!! are those 74 cfm delta's i see? i have 3 of those in my pc and they get pretty damm loud at high rpm's, however, even a PWM does an ok job, but i want a reho

[RIG RIDER]

96.4 cfm @ 38db x 2240 rpm
WFB1212ME
http://www.excesssolutions.com/cgi-bin/item/ES2909
http://www.excesssolutions.com/mas_assets/acrobat/ES2909.pdf

Ya, I could use some help slowing these puppies down.

[gangaskan]

errr, yeah those are the ones i have haha, i had to double check my model num. i have mine hooked up to a zalman and they seem to be fine, however, you might be off buying 6 single reho's and modding a bay panel thats what i would do

something like this ?

http://www.performance-pcs.com/catalog/index.php?main_page=product_info&cPath=137&products_id=21101

[RIG RIDER]

I really would like one rheostat and no bay device.
I know that might not be possible but I'd like to see if it is.

[meionm]

Push pull config does't work, so you could ditch three fan. If you won't find speed controler, you could make a switch. A switch that would let fans either run at 7v or 12v

[ctrl_alt_del_]

wow - isn't 6 Deltas on a BIP a little overkill?

[RIG RIDER]

And your point?
hehehehe....well .....maybe.

[Linux_Box]

There is a store selling a very large rheo...something like 25 watts or so. I'll try to find the link. You can build one quite easily but the cost of the rheo could be high.

Here it is: http://www.sidewindercomputers.com/sirh25wa.html

To build your own: http://www.alltronics.com/cgi-bin/category.cgi?item=100RH25

or

http://www.surplussales.com/Potentiometers/Rheostats/PotsRheost-3.html

Now your next question on the build your own is what resistance, ohm, do you need. I'll find a link for it if you want to go that route. Do it yourself is uber, uber easy.

[Linux_Box]

OK..you got me started on building my own again.

Here's a link: http://www.cpemma.co.uk/rheo.html

You can do some math to figure it out. Now I'm going to get rid of my 12v/7v switches for another rheo...thanks alot. :p

[RIG RIDER]

Wow I'm lost and electrically challenged, and as well with the math.
I hate to admit this but I need the Dummy version of this.

I can solder with the best, but I need a map.

[Froggy]

Why aren't your fans close to the rad frame? Is the perspective bad, or is your fans blowing air out the side of the rad instead of all the air thru it?

[noxqzs]

I have a few fans similar to yours and was testing them earlier. If your goal is to silence the fans, the cheapest way would be to run them in series in pairs. All this would require is you rewiring them to work on 6v.

http://home.comcast.net/~noxqzs/pics/fansetup.jpg

Basically take 2 fans, RED from one to BLACK of the other, then the remaining to Positive and Negative power source. This way is nonadjustable, but quick and easy.

[djgizmo]

Good Idea! Hmm, would have never thought that 12v fans would still function properly on 6v.

[RIG RIDER]

I have a few fans similar to yours and was testing them earlier. If your goal is to silence the fans, the cheapest way would be to run them in series in pairs. All this would require is you rewiring them to work on 6v.

http://home.comcast.net/~noxqzs/pics/fansetup.jpg

Basically take 2 fans, RED from one to BLACK of the other, then the remaining to Positive and Negative power source. This way is nonadjustable, but quick and easy.
That is a great way to do that, thank you.

I would still like to control the rpm of all 6 Deltas with the turn of one knob.
If anyone can help in my quest to control my Deltas please post your ideas.

[Roofles]

Well, you know the current draw of each fan, .42A , which means the current draw on your 12V line for all the fans is 2.52A. Now you don't really want those fans to run lower than 7V because that can mess with the motor. This means we want to drop 5V across a rheostat. Using V=IR we can divide 5V by 2.52A and get about 2 Ohms of resistance. Also we can find the power dissipation by P=VA, so 5V * 2.52A is a ~12.5W. One rule of thumb in power (heat) dissipation is that the part should be rated for twice whatever its steady state load is at, in this case about 25W.

So after all that, what you are looking for is a ~2 Ohm, 25W rheostat. To control everything after that, connect this rheostat in series with your 12V rail and connect all your fans in parallel after this, and ta da! You have one rheostat and 6 fans being controlled!

Edit: here is a random link for exactly what I described, http://www.surplussales.com/Potentiometers/Rheostats/PotsRheost-1.html for $8 bucks.

[Froggy]

Here is a pre-built 25 & 50 watt rheostat!!!

http://www.sidewindercomputers.com/sirh25wa.html


http://www.sidewindercomputers.com/si50warh.html

[RIG RIDER]

Well, you know the current draw of each fan, .42A , which means the current draw on your 12V line for all the fans is 2.52A. Now you don't really want those fans to run lower than 7V because that can mess with the motor. This means we want to drop 5V across a rheostat. Using V=IR we can divide 5V by 2.52A and get about 2 Ohms of resistance. Also we can find the power dissipation by P=VA, so 5V * 2.52A is a ~12.5W. One rule of thumb in power (heat) dissipation is that the part should be rated for twice whatever its steady state load is at, in this case about 25W.

So after all that, what you are looking for is a ~2 Ohm, 25W rheostat. To control everything after that, connect this rheostat in series with your 12V rail and connect all your fans in parallel after this, and ta da! You have one rheostat and 6 fans being controlled!

Edit: here is a random link for exactly what I described, http://www.surplussales.com/Potentiometers/Rheostats/PotsRheost-1.html for $8 bucks.

I hope your right, cause that's $20. cheaper than anywhere else.
Thank you.

[Roofles]

I can't verify that the random link I found is a quality dealer. I hope so for your sake.

No problemo!

[Malpine Walis]

If you are still working on this, there is another way that you can go about it for less money. A voltage divider is not all that hard to put together and will give you a few steps to select from. Here is the basic circuit:

http://i33.photobucket.com/albums/d93/MalpineWalis/divider.jpg

And the resistor that you would use would be this one:
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=321

Roofles can check my math but that should put you pretty close for under $10 total cost.

[JimmyG]

If you are still at it, here is a complete how to do it for a pulse width modulation circuit that will easily handle all 6 fans and won't generate any extra heat in your case: http://www.cpemma.co.uk/pwm.html

This is really easy for anyone that can use a soldering iron.

I recommend the "Nomad" version of the circuit because the parts are easily obtained. Use the "TIP 1xx" transistor for yours to handle the high current draw.

[Skeith]

people really need to stop thinking about these rheostats and get PWM to controll motor speeds. Rheostats are highly ineficient, not only to they burn up the excess energy as heat thus wasting power, at low voltages the fans loose torque and power.

A good PWM is the most efficient way to go. It switches the fan on and off at a high speed. Becuase the fan is run at its rated voltage (12v) and not 7v 5v or whatever else you may set it at, they dont loose torque or power. Also because the fans speed is controlled by the amout of time the fan is on or off, (duty cycle) you arent wasting power by turnign it into heat with a rheostat (which is just a large variable resistor). Resistor devider networks, or voltage deviders are the same idea, it uses resistance to bias the voltage and turn the rest of the energy into heat.

The 7v mod, while quick and easy is also inneficient since the fans arent running at their rated voltage, however it is more eficient since there is no rheostat to waste power into heat.

Ill tell you, as somone who builds this stuff, and know the theory behind it, stay away from rheostats. Also the reason rheostats are expensive is well,.. they're obsolete. Everything that requires power controll now adays is all done with a form of PWM or phase alteration (like PWM but for AC voltages) because its much more efficient, in some cases more than 80% more. No rheostats, and because of that they dont manufacure them as much so they are expensive.

You can build a PWM for peanuts. The simplest one requires 1 IC, a NE555 timer and a power transistor or MOSFET to controll the output, and a few resistors and capacitors to controll the duty cycle.

[Roofles]

Don't get me wrong Skeith, I agree with you here, but you have to make a concurrent 6 channel PWM, which although not hard is not as easy as one rheostat.

[Skeith]

Don't get me wrong Skeith, I agree with you here, but you have to make a concurrent 6 channel PWM, which although not hard is not as easy as one rheostat.
...um no? 1 channel, he wants to controll the fans at the same time. All he needs to make sure is that the power device doing the switching can handle all 6 fans, wich isnt that hard since most power transistors can switch 8Amps or more.

[RIG RIDER]

Maybe you could draw a plan to show folks like myself who are not as knowledgeable as you are, what you are describing.

[JimmyG]

If you are still at it, here is a complete how to do it for a pulse width modulation circuit that will easily handle all 6 fans and won't generate any extra heat in your case: http://www.cpemma.co.uk/pwm.html

This is really easy for anyone that can use a soldering iron.

I recommend the "Nomad" version of the circuit because the parts are easily obtained. Use the "TIP 1xx" transistor for yours to handle the high current draw.
If you go to this website, it will lead you by the hand. It is a very well written and illustrated website.

[Roofles]

...um no? 1 channel, he wants to controll the fans at the same time. All he needs to make sure is that the power device doing the switching can handle all 6 fans, wich isnt that hard since most power transistors can switch 8Amps or more.

Er crap, I just realize I said that wrong. For whatever reason I was thinking 1 mosfet per fan, but yeah you could do that with one power mosfet... my fault.

RIG - Skeith posted a version of a good PWM controller in one of the stickies, he has some pretty well explained details.

JimmyG also posted a version of the same thing with a different configuration, both should work well.