Maximum PC

Awesome guys - thanks. I'll fiddle with that and let you know how it goes. In the meantime, thanks again for the great advice!

EDIT: I think I'm going to try the circuit first and see what happens. I love the smell of solder in the morning!

Ron,

I dug up my Multisim and found the IRF510, but only found a 3 pin one. Did you add in the extra diode? From the diagram, it looks like a database part.

That is how the part come out of my parts library. I should have covered that. The device is actually as you saw a 3 pin TO-220 case device. The diode you see that looks like part of the device in fact is. The 1N4000 series diode I have in there is to snub any inductive kick from the fan motors.

I wish I would have had time this weekend to run the actual circuit but it should run fine.

Ron

I was trying to sim it before building it. I'll dig around and see if i just overlooked that one or not.

The part I pulled is out of a TO-220AB.

Could you save the circuit and e-mail it to me? jsgaggero, gmail.

The case is a TO220AB so my bad again. The schematic I posted was done using Orcad Capture for schematic. I did the drawing on a page with other small drawings then did a copy and paste into photo shop to get the .gif file I posted. Unlike my version at work the version of Orcad I use at home doesn't include a simulator. No surprise as we pay 10 grand per seat license for the sim and board development package add on.

I could export the schematic file as a EDIF or DXF and send it to you but you would get all the other garbage on the page? There isn't much to the file or actually schematic. A few parts and that is about it. I think I labeled all the parts.

Ron

That's alright, i'll keep on playing with it and see if i can get it. I did get everything added and laid out like you have it, the only thing that is different is that my IRF510 doesn't include the diode in the schematic - has to be the same part, just illustrated differently I guess.

I ran the sim and am getting only 0.018 mv across the motors, though I used a dc power supply for the PWM of the MBD.

I'm looking through the PWM controllers now and I'll try to replace the dc supply with a subcircuit containing the PWM controller, if I can get that to work.

It is my part. If I open my IRF510 in Orcad I get the part you see. However, just for the hell of it I opened it in Eagle and guess what, there is no diode in the part.

I won't have an opportunity till this weekend but I do have the parts to breadboard and try the circuit. I have a pile of fans too!

Ron

Cool - thanks!

I've been toying with this idea for a while, so a few more days isn't that important.

Thanks Ron!

Enjoying a 3 day weekend so I bread boarded the little thing this morning and it actually works just fine as drawn. I used an old Intel 875 PBZ board in an old P3 system that I use for experiments. The board actually had three fan speed control headers but now has two.

I toasted one but it matters not. Anyway I used the PWM signal to drive the circuit and the MOSFET doesn't even begin to get warm.

Something to note (and where I screwed up) is the PWM is tied to the fan Negative much as drawn in the add on circuit. The CPU fan positive is maintained at +12 volts constant and they PWM the negative side of the fan.

If you wanted to get slick about this rather than use the PWM from the motherboard you could drive the MOSFET using a 555 timer chip to generate a PWM signal and have a small pot to adjust fan speed for a half dozen fans or more. I powered three.

Ron