Can you change a fan's internal wattage?

I was looking through fans (trying to figure which ones I want to buy), and I noticed that the more watts a fan uses, the higher CFM it is. There are other factors, like fan depth, blade angle, blade shape, etc. For instance, the Sunon 120x38mm fan is 108 [email protected], whereas the 120x25mm is [email protected]. The YS Tech 120x38mm is [email protected]. Big difference there.

But still, is there a way to remove some sort of resister to allow more wattage (but NOT voltage!) into the fan to increase it's overall CFM, then use a rheo to gain a wider range of control over the fan?

Hoot, I'm expecting you'll find this one.

ive been thinking about this lately. perhaps we design/mod a fan that is perfect for the ocer, perhaps with auto heat based speed control. looking forward to knowing what ya find.

ed8150 said:

ive been thinking about this lately. perhaps we design/mod a fan that is perfect for the ocer, perhaps with auto heat based speed control. looking forward to knowing what ya find.

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Well, my idea was to increase CFM without increasing voltage. You can only take 12 volts, but if it's possible to suck more wattage off the PSU to pump the total possible fanspeed (ans subsequently CFM) up, OCers would have more control over their fans. If you leave the room, crank that mofo up to 8 watts, 162CFM. If you're back, take it down to 80CFM@4 watts. =)

P (Watts)=VI. Put in a smaller resistor and hope the motor doesn't burn out

you'd have to crack it open and respool all the coils to change it's wattage. Be easier to just overvolt it!

Well which is it, respool or change a resistor? Respooling would just change the torque and/or rotation speed, ala RC car motors (twelve turn double, eighteen turn triple, etc), wouldn't it? Wouldn't the resistor change VOLTAGE and not wattage? My aim is exclusively wattage.

yah, a respool would change rotational speed- that's what you want isn't it? same goal, different path.

Since all computer fans are made to run off a PSU that puts out 12V, wouldn't they naturally design the fan to run at 12V natively- What resistor is there to change? hmm, i wish i had a dead fan around here to pick apart do I could look at the thing's innards!

That may be the best way to find out- dissect a fan, and look for components between the hub and +12V input and start measuring em

Über~PhLuBB said:

Well which is it, respool or change a resistor? Respooling would just change the torque and/or rotation speed, ala RC car motors (twelve turn double, eighteen turn triple, etc), wouldn't it? Wouldn't the resistor change VOLTAGE and not wattage? My aim is exclusively wattage.

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V=IR (Ohm's Law)

V stays constant at 12v since that's the only thing the12v line will put out. Since V is now a constant, I and R and inversely proportional. I will go up if R goes down, and R will go up is I goes down. Plug in some numbers and you'll see that it's true.

P=VI (Watt's Law)

Once again, V will be a constant 12v. That makes P and I directly proportional. Increase I, and so will P. Increse P and so will I.



V=Blv (Generator Formula)

I haven't had much experience with motors, but I'll see if respooling the fan would work. Once again, v is a steady 12v. B is the magnet's magnetic field strength, so that will be constant as well. So changing the length of the coil will increase the velocity, V. It's up to you what you want to do

I believe you are beating a dead horse

If you want more wattage you must increase the windings.. changing the pitch will slow the motor down and maybe or maybe not increase cfm (will increase wattage a little).. Its much like variable pitch props on a plane you add more pitch.. it bogs the motor down you then will need more power to keep the revs up..in a motors case you will have to add windings to keep the revs up.. Your best bet is going to be buying a fan that is suited for your needs or overvolt it.. most fans are pretty tolerant to 15 volts and i have gone as high as 18 but melt down is probable in long term use at 18 volt.. If you really want to O/C your fans that your best bet is to find an electrical liquidators store and purchase an adjustable power supply.. then you can use a relay off your PSU to power the unit up.. this way you can run your fans at whatever voltage you so desire

Über~PhLuBB said:

But still, is there a way to remove some sort of resister to allow more wattage (but NOT voltage!) into the fan to increase it's overall CFM, then use a rheo to gain a wider range of control over the fan?

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If you have soldering skills, the components to build a fan controller capable of overvolting to 15v are available at your local Radioshack.

I have put together 3 of the units (two of which I didn't trust) found here at hardware-corner.net and the final unit works great. As walaka mentioned, you do take the risk of destroying a fan. A multimeter is a big plus when building one of these setups. The attached setup from hardware corner uses the LM317 voltage regulator in conjunction with a mechanical rehostat to control a wide range of voltages.

I have some pictures and details in an earlier thread ]here. They're fairly straightforward to build. A smaller tip iron is suggested. I'm working on a writeup on a lot of this stuff but I've got a ways to go. Might be a better idea to just get a different fan depending on your situation. Good luck with your final decision.

Well it looks like you are up for a project. Instead of trying to push more amps into your fan (which is basically what you need to do if you want the voltage to stay the same) why not consider a stepper motor for your fan?

If you have an old floppy drive that you do not mind breaking up, then you already have the motor and a controler chip for 12 volts. If you want software control, you can drive it from a parallel port.

Here is a link to a page with lots of useful data on the subject.

Hm. I was trying to figure out a way to turn a $10 fan into a $15 fan. I guess the effort isn't worth $5. Eh well, project scrapped.

wire it up to the main atx connector you can volt it out to 15 17 and 24 and it only takes like 2 mins. ie ran a generic radioshack 120mm fan at 24 for a month or so no noticable damage it still works

Why not try a mains powered fan, you can get them 110 mm, looks just like a 12v, and use a light dimmer to control it.

just my 00.02c worth