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Old 24th March, 2002, 04:26 AM
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What is the difference?

Here is a link to OCMod's variable speed controller circuit layout: http://www.ocmod.com/code/show_art.php?id=4&pg=3
Why doesn't one just connect the fan where the voltage regulator chip is? In fact, what is the purpose of the voltage regulator chip? The chip will only recieve a fraction of the input voltage to begin with, why can't this voltage be applied directly to the fan?
My idea for a variable speed controller is simply a voltage divider circuit using a potentiometer: http://www.columbia.edu/~apd2002/images/circuit.gif
I'd probably select a potentiometer with a resistance which is close to the effective resistance of the fan.
What is the difference between what my circuit does and what OCMod's circuit does? Obviously OCMod put the voltage regulator in but what is its purpose and why is this better than my circuit?

Thanks,
Claudius
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Old 24th March, 2002, 04:58 AM
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If you just want a mod to drop the volts on a fan all you need it a switch, and on one side put normal, and on the other resistance. You can use a rheostat to have variable resistance, or use the formula;
(Device voltage - Desired voltage )/ Device Amperage = Ohms.
and just use a resistor. (make sure it is the right wattage)

Here's a diagram of the one I'm building, well I wired it I just need a dremel and the rheostats to finish.
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What is the difference?-untitled.jpg  
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Old 24th March, 2002, 06:55 AM
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You boys really should use voltage regulators. Solid state parts are more reliable than mechanical parts. Rhesotats alone work, but I wouldn't trust them in mission critical applications.

Satan, that is the worst electical schematic I've ever seen, it took me 5 min to figure out what was going on! Would have been nice if you had labled the the DPDT switches at least!
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Old 24th March, 2002, 07:49 AM
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MAKE SURE that you use a 5 WATT pot. Anything lower will get pretty damn HOT!!!

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Old 24th March, 2002, 07:53 AM
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Quote:
Originally posted by dimmreaper
that is the worst electical schematic I've ever seen, it took me 5 min to figure out what was going on!
I know, it's very sloppy and unprofessional, but you can sort of get what's going on. I don't know how to make good schematics.
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Old 24th March, 2002, 03:45 PM
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Quote:
Originally posted by satan


I know, it's very sloppy and unprofessional, but you can sort of get what's going on. I don't know how to make good schematics.
Electronics workbench. Great program or Autocad with the elec plugin.
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Old 24th March, 2002, 05:15 PM
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Quote:
Originally posted by satan
If you just want a mod to drop the volts on a fan all you need it a switch, and on one side put normal, and on the other resistance. You can use a rheostat to have variable resistance, or use the formula;
(Device voltage - Desired voltage )/ Device Amperage = Ohms.
and just use a resistor. (make sure it is the right wattage)
Actually using a voltage divider will give you more predictable results. I still don't understand what the purpose of the voltage regulator chip is though.
Why should you use it? What makes it more reliable? Is OCMod.com using it correctly?
My questions more concern this chip rather than how to make a rheostat.

Thanks guys,
Claudius
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Old 24th March, 2002, 06:37 PM
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Begin rant. Why oh why can't people run fans as God intended them to be run? 12 Volts, end of story.

AFAIK, every method of reducing the fan's voltage has a drawback. Rheostats/Resistors waste power and get very hot. The Switching method is said to have problems in making a fan that's at a dead stop spin up at all.

Why not think ahead? Buy the fans with the cfm you need in the first place.
"But my CPU needs more cooling at load than at idle." This will never change, arrange your cfm to handle full load. Then forget about it.
"But my pwecious wittle ears!" Grow up, or go with lotsa case cutting and lots of low volume/low noise fans. Or water! Rant over.
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Old 24th March, 2002, 10:35 PM
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Why can't I run my fans as god intended them? Personally, my computer will lock up unless my fans run full blast while at full load or while I'm playing games. BUT, I also want to sleep with my computer on. My fans are just too darn loud at full blast; I have to shut my computer down at night. So what is my solution? Well, I don't have much money to work with here. I'm not about to lay down $200 for a water cooling system or even a new motherboard that will handle full load better. Therefore buying a $3 potentiometer from RadioShack to cut the voltage to my fans seems like the best idea to me. Still , I do not want to do a half-assed job. I came across a circuit which uses a voltage regulator chip. This chip seems completely pointless to me and no one has been able to tell me what good it does. Why should I use this chip in a circuit?
Sure I'm being a baby, but I don't have nearly the money to throw around that some of you guys do, nor do I have the tools here to do many projects.

Simple answer to my question would be fine, thanks.

Claudius
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Old 25th March, 2002, 06:55 AM
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Very good points, Claudius! And welcome to AOA's Forums! Whew, glad I bracketed my post with rant warnings. Close one there!

I can't deny that I can't sleep with a Delta Screamer six feet from my ears. 16 hours a day is bearable, but those Screamin' Banshees just get under my fingernails at night. Perhaps you need to keep your box on 24/7. If this is so, you might think of buying a ~33 cfm 60mm fan to replace a Delta 38. Or a fan adapter and a 80mm fan to replace a Delta from hell-a.

I'm well acquainted with the exigencies of a limited budget. I have no sig listing all my fabulous collection of PC components.

Sorry that I can't be of real help with your Q. My bad.
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Old 25th March, 2002, 11:38 AM
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Quote:
Originally posted by cloasters
The Switching method is said to have problems in making a fan that's at a dead stop spin up at all.
This is news to me! Switching regulators are known for their superier low speed regulation and standing starts over a linear regulator!

Generally when you have a motor that requires a slow start from stand still you'd use a switching regulator because a linear can't do it.

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Old 25th March, 2002, 07:21 PM
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Thanks Cloasters! Sorry if I sounded irritated.
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Old 26th March, 2002, 10:48 AM
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Using just a rheostat to control the fan speed is an Un-Elegant solution. Rheostats arent the most relaible of components, especially when loaded up with 5 or so watts.
Using a voltage regulator means you can buy a much cheaper rheostat, which will be more reliable because the regulation of voltage isn't being done by a mechanical component, its being handed over to a solid state device.
Also, a voltage regulator can handle over 20w if heatsinked up if i recall correctly.
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Old 26th March, 2002, 06:02 PM
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Quote:
Originally posted by Dave
Using just a rheostat to control the fan speed is an Un-Elegant solution. Rheostats arent the most relaible of components, especially when loaded up with 5 or so watts.
Using a voltage regulator means you can buy a much cheaper rheostat, which will be more reliable because the regulation of voltage isn't being done by a mechanical component, its being handed over to a solid state device.
Also, a voltage regulator can handle over 20w if heatsinked up if i recall correctly.
Alright then what is the proper way to use one? The way OCMod.com used it (see the link at the top) seems pointless to me. I could be wrong, but it looks like the rheostat is cutting the voltage and this voltage is being fed to the voltage regulator to do nothing except create that voltage with respect to ground.
So whats the deal?
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Old 26th March, 2002, 11:56 PM
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A linear regulator works off of an error amplifier that compares the voltage at the output pin with that at the ground/adjust pin. Increasing the voltage supplied to the ground/adjust pin increases the output voltage, decreasing the voltage supplied to the ground/adjust pin decreases the output voltage. The ground/adjust pin draws very very little current, so you can use a very small very cheap trimmer as Dave pointed out.
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Old 27th March, 2002, 12:02 AM
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Im currently working on a circuit controlling my radiator fan using a thermistor and an Operational Amplifier, it doesnt vary the speed as such, but switches the fan on and off at a certain temperature. Some people would see this as a bad way of controlling a fan, after seeing all these fully variable ways about.
Basically im just fooling around, if it works okay itll get relegated to my sisters PSU fan, if its really cool (whcih i doubt) itll stay on my box.
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Old 27th March, 2002, 12:50 AM
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I've been toying around with the idea of building a thermostaticly controlled variable 8-14V stetp-up/step-down switching supply to control my radiator fans. It'd be nice to keep my water temps precisely 2C above ambient.
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Old 27th March, 2002, 04:44 AM
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Oh, the ignominy. I better start remembering the details of all PC centric material I read on the Web. Fuhgettaboud it. Permanent cloaster's disclaimer: I have no degrees in electrical engineering.
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Old 27th March, 2002, 05:23 AM
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i took a different path to noise polution 2nd psu hot wired into my main atx two heavy duty reostats one for the case fans and one for the hs fan and this rig has been running 24/7 for about a year and 2 months no problems yet
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