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Driving 50 fans from one pwm signal - Page 2

post #11 of 58
Quote:
Originally Posted by FireDragon View Post

I don't know enough to "tweak" the 555. However, Bing on the thread referenced by ehume shows a 555 pwm amplifier in post 1606. Reading the 555 specs however, it appears that it can only sink 5ma at 5v (up to 200ma at 12v, but that is not relevant). Since the basic pwm circuit has to sink (if I remember correctly) 8ma, this doesn't do any good.

Because of that I don't see a 555 being useful. Wouldn't a MOSFET be better than a BJT since (while it uses current to charge the internal capacitance) it is voltage controlled rather than current controlled.

I am thinking that something like a pwm signal, pulled up to 5v could be used to drive a MOSFET, which in turn could sink as much current as needed. If that approach would work, then I am on the right track. I don't know enough to specify the pull up resistor or the MOSFET part number. I am assuming the need to drive 500ma (the 1.3 fan spec would require 250ma for 50 fans).

No you don't need a 555. Like you said a million times you already have the PWM signal. All you really need is a transistor to supply a current gain (without voltage gain).

You should probably use a FET since they don't generate as much heat. Since you want current only, probably use a common drain configuration. You basically need an NMOS transistor that can supply a drain current of at least 500mA, probably more just to be safe. Make sure the threshold voltage is less than 5v or you won't get anything biggrin.gif.

PWM to gate, PSU 5v to drain, source is pwm out. Try it and if you blow up your power supply and 50 fans I'm not responsible redface.gif.

No but seriously, you should test it first, I have a general idea that it will work, but someone should double check this. Since it's PWM you're basically using it like a switch so its fairly simple.
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post #12 of 58
It sounds like you already know this, but for what it's worth, here's the details on the pwm wire. It took me a long time to find something like this, that's why I'm linking it smile.gif.
4th pin PWM specs
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post #13 of 58

You could also enter the PWM thread and ask Bing and others your questions. I say enter the thread because your question is interesting.

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post #14 of 58
Thread Starter 
Quote:
Originally Posted by drjoey1500 View Post

It sounds like you already know this, but for what it's worth, here's the details on the pwm wire. It took me a long time to find something like this, that's why I'm linking it smile.gif.
4th pin PWM specs

Thank you. There is a new 1.3 version available. Sorry, I don't have the link (but I did download it when I found it).
post #15 of 58
Ok, since no one else will ask ...

Why on Earth do you need to drive 50 fans with just 1 signal?
post #16 of 58
Thread Starter 
Quote:
Originally Posted by ehume View Post

You could also enter the PWM thread and ask Bing and others your questions. I say enter the thread because your question is interesting.

I already have. Bing hasn't chimed in yet, though. But there are different people on this site vs that. There are also many thousands of threads and a bit of searching has not turned up anything. And I have searched repeatedly on the web and not found anything relevant, which is surprising since a lot of water cooling people will have similar issues with fans. They can't all be using non-pwm fans.
post #17 of 58
Thread Starter 
Quote:
Originally Posted by 47 Knucklehead View Post

Ok, since no one else will ask ...

Why on Earth do you need to drive 50 fans with just 1 signal?

Its part of a long, complex build so I won't go into too much detail. Having said that, I have 4 Black Ice GTX 560 radiators. In a push/pull configuration that will require 32 fans. However, I am planning on building (or me and a local machine shop) a case for the radiators. Given that, I decided to build two fan "walls" 25 fans each. That will provide a built-in fan "shroud" and increase the air flow which will help to compensate for any added acoustic dampening that is required. An Ardiuno 2560 Mega will be controlling everything in the cooling case. Its output pins can sink 40ma, although I would not like to push it that much. One Ardiuno circuit is slated for controlling the fans.

In the first phase, my system will be air cooled. It is up and running, albeit missing a few things yet. The case has 10 fans that need to be controlled. The same solution can be used for that.

In the second phase, I will move to water cooling. Everything related to cooling will be outside of the case. I have a Cosmos II case, but it will have 4 optional drives 4 SSD drives and 10 hard drives. I also don't want any more water in the case than needed. I am modding the case for quick release, low loss connectors so that everything can just "snap" together.

In the third phase, I will add TEC chiller to the water cooling (if needed) to get my 3770K up to 5Ghz. stable on a 24/7 basis. The remaining Ardiuno circuits will be devoted to temperature measurement, flow measurement and controlling the TECs.
post #18 of 58
I have no knowledge on how PWM works so bear with me on this. The problem you say you have is that the PWM signal will become too weak. You also said that you could in some way make a PWM signal with an arduino. Now, couldn't you in theory, make multiple PWM sources powering only a certain number of fans each. I know that would end up taking up a lot of space, and you wouldn't be able to monitor the RPM of those either. But instead of taking one source and trying to amplify it, just make multiple sources calibrated to be the same speed to power x amount of fans each.
post #19 of 58
Thread Starter 
Quote:
Originally Posted by BgG286 View Post

I have no knowledge on how PWM works so bear with me on this. The problem you say you have is that the PWM signal will become too weak. You also said that you could in some way make a PWM signal with an arduino. Now, couldn't you in theory, make multiple PWM sources powering only a certain number of fans each. I know that would end up taking up a lot of space, and you wouldn't be able to monitor the RPM of those either. But instead of taking one source and trying to amplify it, just make multiple sources calibrated to be the same speed to power x amount of fans each.

That would work, although a bit inelegant. It would also require a number of cooperating Ardiunos -- much more complex than a PWM amplifier! And programming would become more complex as well. Finally, I want all of the fans to run at the same speed. By using different PWM circuits, it will be tricker to ensure that they are all getting exactly the same signal.
post #20 of 58
Quote:
Originally Posted by FireDragon View Post

don't know enough to "tweak" the 555. However, Bing on the thread referenced by ehume shows a 555 pwm amplifier in post 1606. Reading the 555 specs however, it appears that it can only sink 5ma at 5v (up to 200ma at 12v, but that is not relevant). Since the basic pwm circuit has to sink (if I remember correctly) 8ma, this doesn't do any good.
Because of that I don't see a 555 being useful. Wouldn't a MOSFET be better than a BJT since (while it uses current to charge the internal capacitance) it is voltage controlled rather than current controlled.
Quote:
Originally Posted by drjoey1500 View Post

You should probably use a FET since they don't generate as much heat. Since you want current only, probably use a common drain configuration. You basically need an NMOS transistor that can supply a drain current of at least 500mA, probably more just to be safe. Make sure the threshold voltage is less than 5v or you won't get anything biggrin.gif.
That's nonsense. Nothing is current controlled http://amasci.com/amateur/transis.html
Also by the way, amplifying PWM on BJTs generate very low amounts of heat because it is either fully on or fully off a mosfet doing the job is going to dump it's RDSon as heat
Using FETs blindly can cause a whole variety of issues on top of that
Also 555 timers can sink at least 50mA on the whole Vin range
Quote:
Originally Posted by FireDragon View Post

That would work, although a bit inelegant. It would also require a number of cooperating Ardiunos -- much more complex than a PWM amplifier! And programming would become more complex as well. Finally, I want all of the fans to run at the same speed. By using different PWM circuits, it will be tricker to ensure that they are all getting exactly the same signal.
A pin on each Arduino (Why does everyone use arduino ... sigh) to act as a output to sync with other arduinos (a input of course on the others)
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