PWM to Analog converter circuit

Decided to go ahead and build the thing....

Quite a useful board this one. Negates the need for PWM splitters and fan controllers. The fan response curve for the 4x DC fans can be tailored with the separate RPM feedback.

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Board dimensions 75 x 22 x 14mm.
 
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Looks very nice.

PSU power for both converter for 3-pin variable voltage and 4-pin PWM fan headers
PWM control fan plug monitoring rpm for 3-pin variable control fan​
PWM control to both converter for 3-pin variable voltage and 4-pin PWM fan headers
2nd fan plug monitoring PWM fan speed.​

Is that correct?
 
All it need to look like a commercial unit is a little case and braided cables .. but I know that would likely almost double the price.
 
doyll said:
All it need to look like a commercial unit is a little case and braided cables .. but I know that would likely almost double the price.
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That looks lovely (the one with 4 pin and 3 pin); depending on what double the price actually is it might still be worth it/good value. :)

If you were to build it with "proper" fan connectors (with the plastic shroud/key) and in a box with nice cables you may very well have a business on your hands.

Maybe OCUK/CaseKing could distribute it for you? I can see the "8-pack fan controller" being a product, as it has 8 outputs, LOL.
 
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Those proper 4 pin PWM fan headers are quite a bit more expensive than the ones I've been using. I did buy a few of them early on but they were probably the most expensive part in the build. Most of the cost of the boards I sell, and it's only 1 every other month or so these days, is for the time it takes me to build.

Im sure they could be built in China for next to nothing but I'd need to stump up cash for thousands of units. I just don't have the spare money or belief that they'd sell all that well.
 
Tealc said:
Those proper 4 pin PWM fan headers are quite a bit more expensive than the ones I've been using. I did buy a few of them early on but they were probably the most expensive part in the build. Most of the cost of the boards I sell, and it's only 1 every other month or so these days, is for the time it takes me to build.

Im sure they could be built in China for next to nothing but I'd need to stump up cash for thousands of units. I just don't have the spare money or belief that they'd sell all that well.
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Exactly, that's why I was suggesting maybe contacting OCUK to see if they would be interested in maybe licencing the design/paying you royalties/putting up the cash to get started to do it on more commercial basis.
 
AdamScott85 said:
Tealc would you be able to make one of these to run 12 fans? Just wondering as an option.
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Hi Adam. The circuit as it stands isn't ideal for quite so many fans. I did do some ground work a while back on boosting the power capabilty and had some encouraging results but seeing as there was no outlet for these boards I didn't develop further.

My normal method of working around this is to make multiple circuits to spread the load of the fans. In this case 3 x 4 fans. The easiest way to do this would be to make a single PCB with 3 lines of circuits, similar to that imaged a few posts ago but with 3 lines of analog rather than a mixed digital and analog solution. A 12 fan solution would obviously involve a larger board, maybe something like 75mm x 40mm x 14mm (LWH). Load on the PWM channel would be minimal and should not pose a problem. Fan tach output could easily be made on all 3 channels to achieve balance. Power from Molex, obviously. ;)

Was it all 3 pin fans you were interested in using or a mixture of PWM/3 pin?
 
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It would have been a mixture of 3 pin and 4 pin but I am not sure how many of each Tealc mate. There might be 14 fans and not 12, again not certain so will check later and post back.
 
Seems like a good place to ask instead of creating my own thread. (nb: not an electronics guy, this might be a load of pap)

With 3 pin fans, why not pulse 12v to them in a square wave pattern? I'm not sure why all mobos decrease the voltage instead of pulsing 12v? From what I'm reading, this kind of pulsing is how pretty much all 2 and 3pin fans are controlled outside of PC applications?

Since as we all know some PC fans will not start if the voltage is too low, wouldn't it make more sense to control 3pin fans by pulsing the voltage instead of varying it?
 
Good question. It's all about the tach feedback.

If the 12v is pulsed, the whole electronics of the fan are switched off between the pulses. What this means to the hall sensor that sends a pulse back to the motherboard twice per revolution is that it'll work and then not work several thousand times per second and this will cause absolute havoc to speed monitoring. I've seen crazy 125,000 rpm readings using 12v PWM on PC fans and the fan was only spinning at 600rpm or so. When a 2 pin fan is employed in say a PSU it doesn't matter about fan monitoring as they'll design the fan to fit the function.

What a 4 pin fan does is disengage the drive only and keeps the remainder of the electronics active, so the tach will still work.

With the converter circuit I have used there is always some residual voltage in the circuit to keep the electronics active, no matter the current draw, so the hall sensor provides a reliable result, down to about 3v or 4v.
 
So in theory then you could pulse between 12v and 5v, instead of 12v and off?

It's just that I'm reading elsewhere that some mobos, Asus and Gigabyte etc, do use PWM on pin 2 for 3-pin fans...? And others are saying they vary the voltage...
 
FoxEye said:
So in theory then you could pulse between 12v and 5v, instead of 12v and off?

It's just that I'm reading elsewhere that some mobos, Asus and Gigabyte etc, do use PWM on pin 2 for 3-pin fans...? And others are saying they vary the voltage...
Click to expand...

Pulsing between 12v and 5v would provide only a 7v potential difference. This is how the 7v mod trick works. It would work but the fan would be limited to 60% speed.

Motherboards will likely use PWM to drive a DC-DC buck converter. I've not ever looked into it though but expect this to be the case as it's more efficient that way.
 
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In layman's terms, does that mean a variable, smooth voltage output between 12v and whatever? Or does that mean an oscillating output with 12v peaks?

Wish I'd studied electronics at school :p
 
For the tach to work it'll have to be a smoothed voltage, at least to some extent. To be honest I've never bothered to view the fan voltages or PWM signal on my computer to actually see what they look like on my oscilloscope. I may do one day.
 
Carlos, who I sent a build off to a while back, decided to make a few PCBs and sent me a few to try out...

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So I loaded up the components on one of them to see how it looked and how it changed the build time and quality.

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Overall it makes it much easier to build. It's just a matter of shoving a few leads in holes, following the polarity in a few cases and soldering the leads from around back.

I bent the 4 pin PWM connector off to the side thinking it might be nice to have it come out the side, but decided to go back to straight up for the remainder. It is intended for a panel mount Molex but I couldn't find any. I also didn't bother to fit a heatsink to the PNP.

The holes in the PCB were quite tight for the resistors and the larger 330 Ohm resistor barely fit and had to be pulled through with pliers and due to its size had to be vertically mounted.

It certainly sped up the build time, at the expense of a approx £1 per PCB vs a 10s of pence for a length of strip board which requires cutting with hacksaw and drilling of tracks to lay out the circuit. It was much easier to solder and also limits risk of solder bridges and has far less stray capacitance.

If I were to sell these I'd probably have to make a 4 pin extension cable to go with each, otherwise an extra lead would be required.

So many thanks to Carlos for sending me these all the way from sunny Spain. :)
 
I didn't sent them from the sunny part of Spain, but from the good old rainy north :)

I will probably made a corrected version with your suggestions in the future, but I'm having a serious lack of free time at the moment, and my top priority is still figure what P channel mosfet and other components you use in that Youtube video where you drive 8 or more fans. I still think a version of this circuit driving 8 fans is a godsend for watercoolers.
 
FQP27.... something. I can't remember but it's written on the bag in the video where I control 10 fans. I took a screenshot but I can't read my own writing fully... As for the rest of the components it was largely the same, although I do seem to remember swapping in resistors somewhere.

It was selected because of low rds on and logic level operation. Goodness knows where the bag is now though to verify.

I'm currently looking at the Phanteks hub and seeing how that operates on heavy loads. Well, I will be when I get a chance.
 
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