Over spin your fans!

[QSDT]

Has anybody tried this and would it be safe look here:http://www.afrotechmods.com/fanmod.htm

And for those in the know where would I put a rheostat in this circuit? In series or parallel? I think I'll give it ago.

[Gizmo]

I wouldn't recommend it at 24v. You might try 17v and see how long it lasts, but you are for sure going to reduce the life of the fan. How much? Dunno. I'd be surprised if the fan lasts more than a week at 24v, but you never know. At 17v, it could last several months.

[QSDT]

So what I'm going to do is build a pulse width modulation circuit with a thermal diode to control my fan speeds on my radiator up to 17 volts. I'm going to hate writting this code!

[Samuknow]

Question is WHY?

Most fans are plenty loud...We ususlly try to lessen it. I understand the to see if I could issue. Most things I do fall under that catagory. I tend to think the added noise would out weigh the added air flow.

I also wonder about causing an issue with the board. I have an electronic relay that runs my water pump. 120 V AC. I tapped off of the 5 V and had issues when I shut down. Killed the bios 2 times. Had to put a diode across the input to prevent the reverse current from messing up my board.

Not trying to rain on your parade. Not intended to offend either.

[QSDT]

No problem and no offense taken, but with the PWM circuit it will also turn the fans all the way to off, so I'll like 17 volts for quick cooling if comming from the fans being off or at very low speed.

[Samuknow]

I have 2 120's (push pull) on my rad. @ 12 V they put out a crap load of noise and air. I can't imagine @ 17 V. I think my rig would probably move across my desk.

Keep us posted...

[Gizmo]

Originally Posted by QSDT

So what I'm going to do is build a pulse width modulation circuit with a thermal diode to control my fan speeds on my radiator up to 17 volts. I'm going to hate writting this code!

'twould be quicker and easier just to use a little 555 timer as your pulse-width modulator, with the thermal diode controling the cycle period, IMHO.

[QSDT]

Would I need 2 x 555 or just one 556 for PWM's? Or I'll go with an OP-AMP. Thanks for the idea they are cheaper.

[Aedan]

Decent fans should be happy running at 15V for extended periods of time. Cheap fans will probably not be.

However, also remember that the -12V line on the PSU is not designed to provide very much current at all. For example, the Enermax ELT620AWT can only provide 7W of power on the -12V line. Running the your fans on higher voltages increases the power they take, so be aware you could do damage to the PSU!

[skool h8r]

Originally Posted by QSDT

So what I'm going to do is build a pulse width modulation circuit with a thermal diode to control my fan speeds on my radiator up to 17 volts. I'm going to hate writting this code!

Off topic: You mean you're a software developer as well? You learn something new every day.

[Gizmo]

Originally Posted by QSDT

Would I need 2 x 555 or just one 556 for PWM's? Or I'll go with an OP-AMP. Thanks for the idea they are cheaper.

You should be able to do it with a single 555, but since 556s are cheap as chips too, you could use a 556 and maybe use the other half of the chip to flash an LED or something.

[chrisbard]

Or just go buy thermaltake fan kit and get speeds from 1300 rpm to 3000 with all 4 80mm fans like I did and I am very happy !

Tt 4Channel VR Fan Kit

[QSDT]

LED with temp showing, you are tempting me. Now drolling like Homer Simpson. Oh and I was going to hate writting the code for ''AVR micro'' because I'm not very good at it at all would take me some time, but the wisdom of gizmo to use a 555 or 556 will save much time and $$.

[BobRoss]

Originally Posted by Samuknow

I have 2 120's (push pull) on my rad. @ 12 V they put out a crap load of noise and air. I can't imagine @ 17 V. I think my rig would probably move across my desk.

Keep us posted...

Do you notice a temp drop from the 2nd fan? I just ordered a 3 fam Rad and I am considering using 6 instead but I am not sure there is a bennefit to push pull. Do you notice one?

[Gizmo]

Originally Posted by QSDT

LED with temp showing, you are tempting me. Now drolling like Homer Simpson. Oh and I was going to hate writting the code for ''AVR micro'' because I'm not very good at it at all would take me some time, but the wisdom of gizmo to use a 555 or 556 will save much time and $$.

Contrary to popular opinion, a microcontroller and software is not always a better solution than dedicated hardware....

[Samuknow]

Originally Posted by BobRoss

Do you notice a temp drop from the 2nd fan? I just ordered a 3 fam Rad and I am considering using 6 instead but I am not sure there is a bennefit to push pull. Do you notice one?

The bennefit I see is I am able to run the fans at a lower speed and still acheive the same temps. In tern it is quite a bit quieter. Again every situation is different. Location, where the fresh air is drawn from.

I can't tell you that there will be a big diff in temps. It may be only a degree or two. try both setups if you can.