Trying to follow this pwm fan controller guide...

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DarkenReaper57

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Oct 2, 2003
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Hey, I'm kinda a noob to electronics. I've been doing a lot of reading, but more complicated things like IC's in a circuit are still rather overwhelming.

Anyway, I want to build this PWM circuit here: http://casemods.pointofnoreturn.org/pwm/circuit3.html.

Now, I'm also a noob to matching electronic parts (specifically IC's). I wanna try to get everything locally at radioshack if possible since shipping usually kills any decent buys online.

Is this the same as the uA741P op-amp as described in the guide? http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=276-007. If not, why and where can I find out?

Oh, another thing - I would like to modify the circuit so I can use 2 or 3 total pots to regulate different fans. How would I go about doing this? Would I need to use one IC for each pot?

Thanks.

EDIT: Is there also anything at radioshack that will work instead of a 2n222 transistor? I can't seem to find that one...
 
I might actually go with this guide instead due to simplicity and the fact that I want 2 or 3 different channels. If I go with this, I can simply make 2 or 3 different linear circuits. http://casemods.pointofnoreturn.org/vregtut/tutorial-full.html

The downside with this is I need a heatsink to dissipate at least 6.12 watts on each regulator (since this is the input power on the 120mm U1A). Is a linear regulator impractical at this point?
 
Is this the same as the uA741P op-amp as described in the guide? http://www.radioshack.com/product.a...ct_id=276-007. If not, why and where can I find out?
Click to expand...

That should would fine.
The *NC is national's suffixes, N is the package type (DIP) and C is the grade, rated for slightly lower supply votlage (+/-18V instead of 22) and temerature range (0-70 instead of -50-125C), neither of which should cause you any troubles.

Oh, another thing - I would like to modify the circuit so I can use 2 or 3 total pots to regulate different fans. How would I go about doing this? Would I need to use one IC for each pot?
Click to expand...

yea, you can reuse the 555 timer part for all three fans, but the op-amp, pot, and output (including the 2n222 and IRF510) would have to be built for each individual fan.

s there also anything at radioshack that will work instead of a 2n222 transistor?
Click to expand...

This should work. All you really need is a basic NPN general purpose transistor.


You can also consider this cicuirt (as well as many many more).
(You can use the IRF510 in place of the IRF530, 4A continous current is more than enough to drive your fans I gather).
I don't know if it's really any simpler (there are a few other designs that you might take a gander at) but it replaces all the different transistors and ICs with one quad op amp (LM324 availible at RadioShack as well, at leat their online store).


If I go with this, I can simply make 2 or 3 different linear circuits.
Click to expand...

Sure. You can build multiple copies of that to operate different fans.

The downside with this is I need a heatsink to dissipate at least 6.12 watts on each regulator (since this is the input power on the 120mm U1A). Is a linear regulator impractical at this point?
Click to expand...

if you're only putting 500mA through each 317 chip, it's doable.
You can still get that kind of current at Tj (basically the internal temp of the device) over 100C or more, so you ony need maybe a 10-15C/W heatsink for each. You can get two or three of those by ripping apart an old PSU.
I wouldn't say that's a paritcullarly good idea as you do that for 3 fans, and you're dumping an extra 20W of heat in the case.
 
FreiDOg said:
That should would fine.
The *NC is national's suffixes, N is the package type (DIP) and C is the grade, rated for slightly lower supply votlage (+/-18V instead of 22) and temerature range (0-70 instead of -50-125C), neither of which should cause you any troubles.



yea, you can reuse the 555 timer part for all three fans, but the op-amp, pot, and output (including the 2n222 and IRF510) would have to be built for each individual fan.



This should work. All you really need is a basic NPN general purpose transistor.


You can also consider this cicuirt (as well as many many more).
(You can use the IRF510 in place of the IRF530, 4A continous current is more than enough to drive your fans I gather).
I don't know if it's really any simpler (there are a few other designs that you might take a gander at) but it replaces all the different transistors and ICs with one quad op amp (LM324 availible at RadioShack as well, at leat their online store).




Sure. You can build multiple copies of that to operate different fans.



if you're only putting 500mA through each 317 chip, it's doable.
You can still get that kind of current at Tj (basically the internal temp of the device) over 100C or more, so you ony need maybe a 10-15C/W heatsink for each. You can get two or three of those by ripping apart an old PSU.
I wouldn't say that's a paritcullarly good idea as you do that for 3 fans, and you're dumping an extra 20W of heat in the case.
Click to expand...

Yeah, the reason why I'd prefer a PWM fan controller is for the reason of heat. It seems rather counter-productive to dump more heat into the enclosure. I'm trying to keep temperatures as low as possible.

My main problem is I'm still a pretty big noob to electronics. I understand about resistors, capacitors, charge time, simplifiying resistor/capacitor circuits, but not IC's. I'm kinda lost in that department. I don't feel too comfortable modifying a circuit on my own as I don't really know what I am doing. Is it fairly easy for a noob to modify one of the above PWM circuits so I have 3 channels? If so, would you recommend this one http://www.cpemma.co.uk/pwm.html?

I really do want to learn this stuff though. Im an electrical engineering major, but I haven't gotten into my major courses yet (just the calc/physics/etc). It would be nice to get a head start.
 
Depends, do you want 3 seperate channels or hook 3 fans up using the same signal. If you want 3 fans on the same signal that's easy, just hook them up if you can without exceeding the MOSFET's power output.

Making 3 channels from that circuit isn't hard either. You can just replicate the op-amp circuit 3 times fed by the same timer pulse.
 
EventHorizon said:
Depends, do you want 3 seperate channels or hook 3 fans up using the same signal. If you want 3 fans on the same signal that's easy, just hook them up if you can without exceeding the MOSFET's power output.

Making 3 channels from that circuit isn't hard either. You can just replicate the op-amp circuit 3 times fed by the same timer pulse.
Click to expand...

I want to do the latter - that is, use 3 different potentiometers to control each fan individually. You said all I need to do is replicate the op-amp circuit 3 times, so is this the part?



So, you are saying that I just run the 3 op-amp circuits in parallel with the 555-timer circuit, correct? More specifically, I branch out from the 10k resistor to each pin 2 on the op-amps, and branch again from pin 6 on the timer chip to each pin 3 on the op-amps, correct? There are some other connections to be made, but they seem kinda trivial. It seems logical, and if this is correct, it is easy enough.

Am I right?
 
You need to include the potetiometer in your duplication since it's what controls your PWM duty cycle. If you look at that schematic you'll notice that it's 2 seperate circuits, you have the 555 timer circuit and the op-amp/fan driver circuit. The only real connection between them is the pulse from the 555 timer to the op amp. If i had hosting i'd post a picture. You just have to have 3 driver circuits (from R4 / pot. / R5 ) and run your 555 pulse to each op-amp.
 
EventHorizon said:
You need to include the potetiometer in your duplication since it's what controls your PWM duty cycle. If you look at that schematic you'll notice that it's 2 seperate circuits, you have the 555 timer circuit and the op-amp/fan driver circuit. The only real connection between them is the pulse from the 555 timer to the op amp. If i had hosting i'd post a picture. You just have to have 3 driver circuits (from R4 / pot. / R5 ) and run your 555 pulse to each op-amp.
Click to expand...

Ok, I understand now. Thanks for the reply.

Now, in the diagram there is a diode...how do I know what kind to get?

Also, is there something to know about pots and knobs? I don't want to buy a pot and find out the knob doesn't fit.

I am looking at a list of pots here but I am not sure which 10k pot to get https://www.jameco.com/webapp/wcs/s...hType=k&searchValue=10k pot&categoryId=205035.

Does anyone know?

EDIT: Do I need to get a heatsink for the MOSFET? I will be running 1 120mm panaflo U1A per channel (.65 amps at 12V).
 
A regular general purpose diode will be fine, you're not dealing with large currents or huge voltages. It's not in use all the time either, and then only breifly. Get a cheap little 10k pot. since again it's not huge currents or voltages. You may not need a heatsink running just 1 fan per MOSFET. The MOSFET used in that circuit has an internal resistance of around 0.54 ohms. At 0.65A of current you get 0.65^2 * 0.54 = 0.228W of power that the MOSFET has to dissapate. Depending on airflow where you put the controller you may not need a heatsink and probably won't at only 1/4 watt.

Oh.. as for knobs, the description on the pots. tells shaft diameter which is 0.25" for all those... at least the ones I saw. Just look for a knob to fit a shaft of that diameter which is really common.
 
EventHorizon said:
A regular general purpose diode will be fine, you're not dealing with large currents or huge voltages. It's not in use all the time either, and then only breifly. Get a cheap little 10k pot. since again it's not huge currents or voltages. You may not need a heatsink running just 1 fan per MOSFET. The MOSFET used in that circuit has an internal resistance of around 0.54 ohms. At 0.65A of current you get 0.65^2 * 0.54 = 0.228W of power that the MOSFET has to dissapate. Depending on airflow where you put the controller you may not need a heatsink and probably won't at only 1/4 watt.

Oh.. as for knobs, the description on the pots. tells shaft diameter which is 0.25" for all those... at least the ones I saw. Just look for a knob to fit a shaft of that diameter which is really common.
Click to expand...

Does it matter if the shaft on the pot is knurled or not?

EDIT: Nevermind. I see that they make different knobs for different shafts. Something else though - I'm thinking of building and hooking up a 10 element bar graph led to each channel. Here is the guide http://casemods.pointofnoreturn.org/voltmon/tutorial-full.html. Now, I connect the circuit to pin 2 on the op-amp, but it says here http://casemods.pointofnoreturn.org/pwm/circuit3.html that I want to "change the VLo and VHi signals on the LM3914 chip to 4V and 8V." How would I do that?
 
EventHorizon said:
A regular general purpose diode will be fine, you're not dealing with large currents or huge voltages. It's not in use all the time either, and then only breifly. Get a cheap little 10k pot. since again it's not huge currents or voltages. You may not need a heatsink running just 1 fan per MOSFET. The MOSFET used in that circuit has an internal resistance of around 0.54 ohms. At 0.65A of current you get 0.65^2 * 0.54 = 0.228W of power that the MOSFET has to dissapate. Depending on airflow where you put the controller you may not need a heatsink and probably won't at only 1/4 watt.

Oh.. as for knobs, the description on the pots. tells shaft diameter which is 0.25" for all those... at least the ones I saw. Just look for a knob to fit a shaft of that diameter which is really common.
Click to expand...

Well, I made a change. I'm going to have 2 channels instead of 3 due to aethetics and cost. Would I need a heatsink on the MOSFET that needs to dissipate roughly 1/2 W of power?

EDIT: I am still trying to figure out what the author is talking about with "VHi" and "VLo" here http://casemods.pointofnoreturn.org/pwm/circuit3.html. Does he mean RHI and RLO? Forgive my ignorance...I am still learning. How would I go about changing these values to 8V and 4V, respectively?

Help would be greatly appreciated :).
 
Ok, looking at the bottom of this tutorial http://casemods.pointofnoreturn.org/voltmon/tutorial-full.html it says how to change RHI: "One last note - what if I want to use a different high value than 12V - say, 7V or 5V? In this case, get a second resistor and place it next to R1 - connect R1 to it in series, and connect this new one (call it R4) to ground. Disconnect pin 8 from ground and connect it to the middle between R1 and R4. Then, the top LED will be equal to 1.25 * (1 + R4 / R1) - it's identical to a LM317."

Ok, well I want to change RHI (this is VHi, right?) to 8V, and RLO to 4V. Doing some math, I can make RHI 8V with a 6.48k resistor. The closest actual resistors to this are 6.2k and 6.8k.

If I am correct, would simply following this work? Don't I need to do something to make RLO 4V?

Argh, I hate being a noob, lol.
 
Well, I figured most of everything out (I think) in terms of the voltage monitor. I have a few questions concerning the 555/741 PWM fan controlling circuit, though.

I tried to find on several datasheets what terminals on a pot are actually 1 2 and 3. How do I know? I want to properly hook them up to this circuit: http://casemods.pointofnoreturn.org/pwm/circuit3.html.

Are these terminals labeled correctly? I just added some numbers to a pic in mspaint.
pot321.jpg


Oh, one more thing. I changed this circuit so it has two channels, but I want to make sure I did it properly.

Basically, thre are 2 separate circuits...the 555 and the 741 op-amp. The only thing joining the two is the wire from pin 6 on the 555 to pin 3 on the op-amp.

So, I put two pots in parallel with the 9k resistors. Off of these pots is a complete duplicate of the circuit to the right. Here is a basic schematic.

circuit3twochannels.png


Sorry for the crudeness, but you get the idea. This should work, right? I hope so, since I have already built most of it...
 
On the pot, the pins work like this:

The middle pin is equivalent to the "arrow" on the pot in the schematic. So you have pin 2 labeled correctly. The outside pins are the two ends of the resistor.
Looking at your pic of the pot, if you turn the knob clockwise, the resistance between the middle pin and the pin on the left will go down, and the resistance between the middle pin and the right-hand pin will go up. (the resistance between the left pin and the right pin is constant).

<think to myself>If you want the fan to go faster as you turn the knob clockwise, you want the voltage on the negative terminal to be as low as possible....center + left shorted....2-3 shorted...</think to myself>

Yes, you have it labelled correctly.
 
Bump for help with my schematic...this modification should work if I want 2 channels, right? Would I need to duplicate the 9k resistors as well?
 
You would probably be best served by duplicating the two 9kOhm resistors. It's possible to do it without duplicating them, but better to keep them isolated.

To adjust your top speed and low speed, I would personally opt to change R4 and R5 instead of some of the other resistors. As the schematic stands (assuming you will duplicate the 9k resistors), you can go from about 0-12V. As you increase the value of R4, the minimum speed will increase. As you make R5 larger, the max speed will decrease.
 
Mohonri said:
You would probably be best served by duplicating the two 9kOhm resistors. It's possible to do it without duplicating them, but better to keep them isolated.

To adjust your top speed and low speed, I would personally opt to change R4 and R5 instead of some of the other resistors. As the schematic stands (assuming you will duplicate the 9k resistors), you can go from about 0-12V. As you increase the value of R4, the minimum speed will increase. As you make R5 larger, the max speed will decrease.
Click to expand...

Well, I already built the circuit more or less, it just isn't working properly...probably forgot to hook something up or am shorting something.

The voltage going to each pot will be the same if I don't duplicate the pots, so why is it better to keep them isolated? Better practice?
 
The voltage going to each pot will be the same if I don't duplicate the pots, so why is it better to keep them isolated? Better practice?
Click to expand...
The voltage won't be the same if you don't duplicate the 9k resistors--that's the problem. If the two 10k pots are in parallel, they will combine to form less resistance, so the two ends of the pot will have a smaller difference in voltage. A quick head-calculation tells me they will be about 4.8V to 7.2V, instead of approx. 4V - 8V. Which means you're losing the top and bottom 20% of your range.

The reason I said to duplicate the 9k resistors is simply because it makes the circuit easier to debug when things go wrong. Like they just did. I say this because I was a lab assistant for one semester, helping students design, build, test, and debug circuits. Life is much easier when you can componentize (is that a word?) parts of the circuit.

If you have access to an oscilloscope, see if you're getting the sawtooth-like waveform out of the first part of the circuit. Compare the max and min voltages of that waveform with the voltages on either side of the pots. If they're roughly equal, you should be able to get full range (0 to 100% duty) on your fans.
 
Mohonri said:
The voltage won't be the same if you don't duplicate the 9k resistors--that's the problem. If the two 10k pots are in parallel, they will combine to form less resistance, so the two ends of the pot will have a smaller difference in voltage. A quick head-calculation tells me they will be about 4.8V to 7.2V, instead of approx. 4V - 8V. Which means you're losing the top and bottom 20% of your range.

The reason I said to duplicate the 9k resistors is simply because it makes the circuit easier to debug when things go wrong. Like they just did. I say this because I was a lab assistant for one semester, helping students design, build, test, and debug circuits. Life is much easier when you can componentize (is that a word?) parts of the circuit.

If you have access to an oscilloscope, see if you're getting the sawtooth-like waveform out of the first part of the circuit. Compare the max and min voltages of that waveform with the voltages on either side of the pots. If they're roughly equal, you should be able to get full range (0 to 100% duty) on your fans.
Click to expand...

Thanks for the help. I don't have access to an oscilloscope, but I can still troubleshoot with a multimeter (somewhat).

I may just desolder everything, get a new board, and start over (after testing on a breadboard this time, of course).
 
Mohonri said:
What are your 'symptoms' of your non-working circuit?
Click to expand...

One of the fans is always at 12V no matter what the pot is at.

The other can be adjusted, but it seems like the adjustment isn't linear. It is almost as though the fan speed decreases rapidly after the resistance on the pot hits a certain threshold.

I DID good and use a non-polarized capacitor in one part of the circuit where I should have used a polarized one (on accident). I will fix this when I get the chance. Perhaps this contributes to it, but I am not sure.

Is it reasonably safe to desolder IC's and MOSFETS and get them back out of a board w/o burning them up? I have a 40W soldering iron and a desoldering braid.
 
Using a non-polarized cap instead of a polarized one shouldn't be a problem--using a polarized one instead of a non-polarized one WOULD be in some cases.

Make sure the pots you got are linear, not logarithmic or audio. Using a multimeter, check the voltages on either side of the pots(pins 1 & 3). They should be about 4V and 8V.

Desoldering the ICs and MOSFETs shouldn't pose a problem--just don't hold the soldering iron on them too long.
 
Mohonri said:
Using a non-polarized cap instead of a polarized one shouldn't be a problem--using a polarized one instead of a non-polarized one WOULD be in some cases.

Make sure the pots you got are linear, not logarithmic or audio. Using a multimeter, check the voltages on either side of the pots(pins 1 & 3). They should be about 4V and 8V.

Desoldering the ICs and MOSFETs shouldn't pose a problem--just don't hold the soldering iron on them too long.
Click to expand...

Yeah, at this point it is a jungle of wires. I also messed up once before so the back of the board is burnt.

I now have jumper wires so I'll use those instead. I also have more experience so I just want to start over.

The pots are linear, these are the ones I bought http://jameco.com/webapp/wcs/stores...toreId=10001&catalogId=10001&productId=264410

When you say check the voltages on the pots, do you mean turn the pot completely one way, test between one of the pins and the wiper (pin 2), check the voltage, then turn the pot the other way, and test again?

I just want to make sure, and I'm very grateful for your help.

EDIT: One more thing. I have some 2.2k polarized electrolytic caps and many resistors. To avoid buying more, I decided to modify the PWM circuit.

On the page here http://casemods.pointofnoreturn.org/pwm/741.html he gives an equation to change these values. I want a frequency of about 80 hz (for 120mm fans) so here are the values of my results to achieve this:

R1 = 1k (constant from before)
R2 = 2.2k (also constant from before)
C1 = 2.2 uF (changed from .1 uF)
RF = 2.2k (changed from 51k)

I the end, frequency is 81.35 Hz. This is close enough for me. I checked my math several times, and it seems fine, but I'd just like to get a second opinion :).
 
80Hz is too low. PWM is used for motors of all sizes, up to and including 100MW (yes, Megawatt) electric motors that are twice the size of a Lincon Navigator. And the frequency used at all levels is in the tens-of-kilohertz range. You might get it to work at a lower frequency, but I suggest using at least 20kHz to get it out of the audio range.

When you say check the voltages on the pots, do you mean turn the pot completely one way, test between one of the pins and the wiper (pin 2), check the voltage, then turn the pot the other way, and test again?
Click to expand...
That's not what I meant, but you gave me a better idea than what I meant. Test the voltage between pin 2 and ground at both extremes of the pot. You should see about 4V and 8V at the extremes.
 
Mohonri said:
80Hz is too low. PWM is used for motors of all sizes, up to and including 100MW (yes, Megawatt) electric motors that are twice the size of a Lincon Navigator. And the frequency used at all levels is in the tens-of-kilohertz range. You might get it to work at a lower frequency, but
Click to expand...

Wow, are you sure? Take a look at this "For simple brushed fans, used in power drills and other machinery, you regularly see frequencies in the range of 5 kHz to 50 kHz (1 Hz = once per second, 2 Hz = twice per second, etc... 1 kHz = 1000 Hz). However, with brushless fans, the electronics inside need time to detect the fan's position and create the correct magnetic field on its windings. So, for brushless fans, we want between 20 Hz and 160 Hz." from http://casemods.pointofnoreturn.org/pwm/pwmtheory.html

I can surely go higher than 80, but I think the kHz range is a bit too high for brushless fans. Please correct me if I am wrong.
 
Hmmm. That's interesting. I've never heard that reasoning before. I know that the heavy-duty motors I've seen are all induction or permanent magnet motors, neither of which have brushes (these motors are designed to run for 20+ years without stopping, so brushes are a no-go), and they use tens-of-kilohertz PWM.

I don't know whether that guide is correct or not. I can, however, say this: I've built a PWM fan controller with a design only slightly different (and somewhat simpler) than the one you're using. My frequency ranged from ~20kHz to 100kHz. And it worked just fine driving normal computer fans. I also (on a different project) built a PWM drive for a couple DC brush motors. It didn't work until I raised the frequency above about 4kHz (IIRC).
 
Mohonri said:
Hmmm. That's interesting. I've never heard that reasoning before. I know that the heavy-duty motors I've seen are all induction or permanent magnet motors, neither of which have brushes (these motors are designed to run for 20+ years without stopping, so brushes are a no-go), and they use tens-of-kilohertz PWM.

I don't know whether that guide is correct or not. I can, however, say this: I've built a PWM fan controller with a design only slightly different (and somewhat simpler) than the one you're using. My frequency ranged from ~20kHz to 100kHz. And it worked just fine driving normal computer fans. I also (on a different project) built a PWM drive for a couple DC brush motors. It didn't work until I raised the frequency above about 4kHz (IIRC).
Click to expand...

Interesting. I will be sure to experiment with my resistors.

Can you still hear "groaning" of 120mm fans at frequencies in the kHz range? I am not sure if they groan at 80 Hz, but I have heard that they can when the duty cycle is low and the frequency is low.
 
Avoiding 'growling' was one of the reasons I went for the multi-kHz range. Even if there is some 'growling' at over 20kHz it'll be inaudible to just about everyone. I did not get any growling.

It may be easier for you to swap in a smaller capacitor than to play with your resistors--it's only one part to swap instead of two.
 
Mohonri said:
Avoiding 'growling' was one of the reasons I went for the multi-kHz range. Even if there is some 'growling' at over 20kHz it'll be inaudible to just about everyone. I did not get any growling.

It may be easier for you to swap in a smaller capacitor than to play with your resistors--it's only one part to swap instead of two.
Click to expand...

I would do that but I don't want to bother ordering more caps :). I only have 1 polarized capacitor, the 2.2 uF ones.

Swapping in and out resistors isn't a big deal. I have many of them and after all, I'll learn more :).
 
Using a non-polarized cap is perfectly fine--I used one on my PWM controller. If you have a small ceramic (disc-shaped) cap, it'll work just fine.

Do you know how to read that type of capacitor?
 
Mohonri said:
Using a non-polarized cap is perfectly fine--I used one on my PWM controller. If you have a small ceramic (disc-shaped) cap, it'll work just fine.

Do you know how to read that type of capacitor?
Click to expand...

No, but I know that they are .1 uF ceramic caps.
 
Reading caps--it's (almost) exactly the same as reading resistors. Except you're reading numbers, not colors. And it's in picofarads instead of ohms. So a cap marked "104" would be a 1 followed by a 0 followed by 4 zeros, so 100,000 pF, or .1uF

just FYI.
 
Ok, well I've been busy with class and all, but I finally got the PWM circuit built on a breadboard.

Unfortunately, the fans are far noisier when under 12V (namely 7V) than when I run them at 7V via the 7V trick on PSU leads.

Anyway, I've been experimenting with different resistors and caps. I've tried frequencies around 30, 60, 80, 100, 150, 3937, and 5790 Hz.

I either get a low or high pitched "growling" or feedback at these frequencies.

At about 5790 Hz (and simliar frequencies) it seems like my fans don't even adjust their speed properly. It suddenly jumps when they are at 12V, but are rather erratic when below that.

Perhaps the thing about the electronics inside needing time to detect the fan's position and create the correct magnetic field on its windings is true?

Argh, I would hate it if this circuit made the fans louder. The whole point of having this fan controller was to dampen the noise...

Any ideas? Thanks.

BTW, I have the following caps and resistors to play with:

Caps:
.47 uF unpolarized tantalum
.1 uF unpolarized ceramic
2.2 polarized electrolytic

Resistors:
680 ohm
1.0k
1.2k
2.2k
5.6k
9.1k
51k
 
Some fans can handle the high torque geneated by a PWM signal fine, some can't.
easiest way to deal with it is to smooth the output with a capacitor or an inductor into a fairly constant voltage. Experiment with the value, it varies from fan to fan. Start small and work your way up, see what deadens the noise best.
 
FreiDOg said:
Some fans can handle the high torque geneated by a PWM signal fine, some can't.
easiest way to deal with it is to smooth the output with a capacitor or an inductor into a fairly constant voltage. Experiment with the value, it varies from fan to fan. Start small and work your way up, see what deadens the noise best.
Click to expand...

Do you mean "blunting" the PWM signals, as described on pages 2 and 3 here http://www.cpemma.co.uk/an58.pdf?

I may try that. Hopefully I can do it with the caps and resistors that I already have.

It would suck if all of this work and money I spent ended up with a fan controller that is louder than a linear one...
 
Well, I got the blunting of the PWM signal to work, but the fans I am using still didn't work too well with the PWM signal. I experimented with different cap and resistor values for the RC circuit for blunting, but the fans still made noticable, annoying groaning noises.

So, I decided to use a LM317 and build a linear voltage regulator instead using this tutorial http://casemods.pointofnoreturn.org/vregtut/tutorial-full.html.

So far, it works great, except it doesn't output a maximum of 11.5V like it says...more like 9.1V or so, measuring from Vout to ground with a multimeter. This is acceptable, I suppose, but it would be nicer if the max voltage were a bit higher.

I could run a switch to bypass the regulator and run the fans at 12V, but it would be a PITA and I would hardly use it since I was silent fans.

Anyway, here is the problem: I am using the LED voltage monitor described by this guide: http://casemods.pointofnoreturn.org/voltmon/tutorial-full.html.

Now, the high is 12V. I want to get it down to 9V or so, so the LED's all light up at full scale. I have followed the part at the bottom of the guide, but it didn't work. I did the math and I figured that a resistor around 7.5k will do the job.

I did the following:

1. Disconnect R1 from ground. Place new resistor R4 in series with R1, and connect R4 to ground.
2. Disconnect pin 8 from ground (and 4 for that matter) and connect it in between R1 and R4 (thus it is a voltage divider).
3. Keep pin 4 connected to ground.

The total LED's that lit up at full scale actually decreased to 1 or 2. Why is this?

Oh yeah, I did follow the guide and connected the signal out (positive voltage to fan out) on the voltage monitor to the Vout on the LM317 circuit.

Any help or ideas as to what is wrong?

Thanks a ton. This has been rather...frustating...but at least I'm learning a lot :).
 
I would suggest the following: Instead of playing with R1 and the VR/ADJ levels, I would suggest adjusting R3 and/or R2. If the last couple of LEDs are not lighting when you're at max fan speed, it means that the voltage going into pin 5 (SIG) on the LM3914 isn't getting high enough. Either increase the value of R2 slightly or decrease the value of R3 slightly, and put the rest of the stuff back the way it was.
 
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