how many volts does a standard fan use?

ArmoArmo Mr. Nice Guy Is Dead,Only Aqua Remains Member
edited September 2003 in Hardware
a bud of mine is trying to build his own fan reobus or what ever its called and he wants to know many much watts, voltages and amps a standard 120mm and 92mm fans would take to operate

Comments

  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited September 2003
    Standard desktop computer fans are 12v. To be on the safe side, 1a @ 12v (12w) per channel should be more than sufficient for all but the Vantec Tornados and big Deltas.
  • ArmoArmo Mr. Nice Guy Is Dead,Only Aqua Remains Member
    edited September 2003
    so the watts are the volts x the amps?

    hes got another ?

    what would be a goot POT to use, how many ohms and Liener or audio tapper
  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited September 2003
    Yes, watts = volts x amps

    You may want to get your friend to do some reading up on basic electronics before he does this. (This coming from a guy who blows LEDs up- literally- on a regular basis... :rolleyes: ). Pots are a very, very bad idea for something like this. Most of them can only handle 1/4w or 1/2w at most.

    As a side note, for computer applications, you generally want linear taper pots.

    Another side note: the number of watts a resistor has to dissipate varies with the amount of power the device it's connected to draws and the voltage drop the resistor is providing.

    What you're friend is going to want to use is an adjustable voltage regulator. I recommend an LM317T, which is available from <a href="http://www.radioshack.com/product.asp?catalog_name=CTLG&category_name=CTLG_011_002_017_000&product_id=276-1778">Radioshack (part # 276-1778)</a>. It's not quite the right spec for this application, but I've used them before, and they work very well.

    I don't understand wiring diagrams worth sh!t (I got my dad to help me wire mine up...) so I can't help you wire it up. However, I can recommend what you'll need. For each fan your friend wants to control, he'll need:

    1x LM317T voltage regulator
    1x 0.1uf capacitor
    1x 5k ohm potentiometer
    1x 240 ohm resistor (a 220 ohm will work)
    1x 1uf capacitor
    1x Heatsink (radioshack part # 276-1368)

    I also suggest a toggle switch with three positions- one for off, one for adjustable voltage, one for full 12v. Unfortunately, I can't remember what kind of switch this would need to be. I THINK it would be either a SPDT (single pole, double throw) or a SPTT (single pole, triple throw), but I'm not sure.

    He'll also need some way of hooking it all up. I suggest one of the boards that radioshack has that are predrilled but have no circuits on them- you hook things up with jumper wire.
  • edcentricedcentric near Milwaukee, Wisconsin Icrontian
    edited September 2003
    The reason to not just use pots is that when you slow the fan down all of the unused power is turned straight into heat. They are just resistors.

    The other choice, rather than fully adjustable is to use SPTT switches and three fixed voltages say low (7V), med (10V) and high (12V). You only build two voltage reg circuts to feed the 7V and 10V.
  • KhaosKhaos New Hampshire
    edited September 2003
    I highly recommend using fixed voltages rather than pots. Volt regulators work fine, too, but they are relatively expensive, and in truth, you really only need 12V and 7V settings. Most 12V fans are rated for operation between 7V and 13V. Anything more or less than that is out of spec, and over time, will burn out your fan's motor.

    What you need to get yourself are a few ON-OFF-ON switches with one contact per position (i.e. three total contacts). Then wire it up so that the center contact runs to the fan's ground wire (Black). The other two contacts go to the PSU, with one being a normal black GND (To provide for full 12V operation), and the other +5V (Red wire from the PSU) to provide for 7V operation (12-5=7). The hot wires for the fans just get wired into +12V Yellow wire from the PSU or red wire from another fan).

    Something to keep in mind: You can combine as many fans as you like onto a single hot wire (+12V), but EACH FAN or GROUP OF FANS requires its own ground, otherwise you will not be able to properly regulate the voltages. Each fan or group of fans needs to have its own switch, and its ground MUST run all the way back to the fan bus. The hot wires can come from anywhere, as long as the circuit you tap into can support the amps and delivers +12V. I recommend creating a dedicated fan circuit from a PSU cable so as to avoid putting too much strain on motherboard or accessory circuits.

    Oh, and like I mentioned, you can combine fans into groups. A single switch can control two or more fans by comining their grounds before the switch. In this way, if you have two 80MM case fans side by side, you can just control them using one switch (Which is usually the desired effect).

    Remember to always triple-check your fan circuits before you fire everything up. When building any kind of fan bus, the wiring can sometimes get confusing, and plugging in two hot 12Vs to a fan that is drawing amps can lead to a smokey situation... Believe me. It's an easy mistake to make, and costly depending on how many fans are on the circuit. Good luck! :D
  • Straight_ManStraight_Man Geeky, in my own way Naples, FL Icrontian
    edited September 2003
    Yeah, the Panaflos run about .25 to .5 amps(5 flow ranges, higher flow out, more parts of amps), Sunon Ball bearings more like an amp each for big ones, the thermotake fan I use for folks that want 120mm fans runs about .45 amps for the 120 mm, its a TT 12025A 1B1S that starts with 6 V and runs all out at 12 V. That fan pumps 78 CFM EACH.

    Trick with a limited size PSU is to limit fan draw. Other side effect of that is the less amps you have to run for just cooling, the more likely you are to be able to add a DVD burner in place of a CD-RW later.
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