potentiometers? which one do i need?

[cowanrg]

ok, i have 2 panaflo fans (the 120mm 89cfm ones) they are 0.45amps each. wattage is 5.4W

my question: what potentiometer do i need? im assuming a 5W will be ok... i just may lose a little performance, but rarely will these be on full anyway. i will most likely have to use 1 pot for each fan, so that is no biggie. im just wandering what OHM rating i should use? i see anyhting from a 5 ohm to a 5 mega ohm. what is the difference? i have heard that a 10 ohm is what i need, but what difference is there from a 5 -10, or from a 10 - 1K?

also, i assume i want a wirewound... anyone want to help me on this? ideally i would like to be able to hook up both fans to the same pot. (i am technically inclined, and understand electronics fairly well. just never dealt with these before).

[flounder43]

I tried using potentiometers with my Panaflo 120mm fan, none of them worked well for me. If I were to turn them down in the slightest, the fan would stop altogether.

I did some research, and found out there is a difference between a potentiometer and a rheostat, I can't ariticulate the difference right now, however. I was told the a rheostat was the way to go.

Anyway, I purchased a 5 Watt rheostat from sidewinder computers. It slows the fan significantly, but will not stop it...

The fan is 5.4 Watts, I think. I also note that when I have it turned to the lowest setting, the rheo gets pretty warm.

[cowanrg]

yeah, from what i understand, a rheostat IS a potentiometer... but there is a slight difference. i see that a 25 ohm will work well for my panaflo fans. i will try a bunch out before i solder it all together. i have an old power supply, as well as an extra 120mm fan to test it all out on. plus, radioshack lets you return stuff no questions asked.

[Owenator]

Flounder,

I belive you may have ran into an 'audio taper' potentiometer. What that means is teh resistance goes up basically exponentially as you turn them. This leads to a very small usable range of resiatance that slows the fan. You need a 'linear taper' potentiometer which changes reistance like a standard light dimmer. I think the audio taper is mostly used for volume nobs and the like. The reheostats are linear tapers that usually handle higher wattages. Radio shack sells a 25 Ohm rehostat that I have used for three panaflo H' 120mm fans but it got pretty hot.

The best solution IMHO is to make a voltage regulator circuit like Hoot did in his cohesive air cooling article. RS sells a low power voltage regulator (LM317) that is good for up to 1.5W. There are higher wattage ones too you can buy online or at other electronic stores. I'll look for the how too link and post it.

O

[Owenator]

Flounder

Here is the how to article hope it helps. I read in another thread about using 17V to get the output higher I will look inot that looks useful.

O

[jbird]

Watts=V*A, so 12V*0.45A=5.4W. So far, so good. Let's assume you want to vary the voltage on the fan from 6-12 volts. 6 volts across the fan will yield ~0.23A. Your rheostat must drop the remaining 6 volts. The rheostat value then should be 6V/0.23A=26 Ohms. Your power dissipation will be 6V*0.23A=1.38 Watts. A good rule of thumb is to double that power value; and as it turns out, there are standard 3 Watt devices on the market. Here's the problem - assume you want 9 Volts on the fan. This will yield around 0.34A through the circuit. The rheostat setting will be 3V/0.34A=8.8 Ohms. The power dissipation will be 1.02 Watts. We had chosen a 3 Watt device - the rating of the ENTIRE part - in our initial calculations. Your new 1.02 Watt dissipation is now occurring along the 34% of the rheostat that is now in the circuit (the other 66% is not conducting current!). Remember the x2 rule of thumb for power dissipation? You need 2W to properly dissipate the power in that 34% of the rheostat. This now requires a 6 Watt device! And so it goes. Personally, I'd use a variable switching power supply, although others are claiming good results using the LM317 linear regulator. Hope this helps! :cool:

[Dissolved]

do anyone know of any rheostats higher then 5watts? im getting a new delta fan, and the 5watt rheostats wont handle the power i belive :(

[jbird]

How about placing some limitations on the problem? What voltages do you really want the fans to "see"? It may be much cheaper (and easier!) to use some discrete power resistors and switch them into the circuit. Otherwise, a variable power supply could do the trick.

[Dissolved]

Originally posted by jbird
How about placing some limitations on the problem? What voltages do you really want the fans to "see"? It may be much cheaper (and easier!) to use some discrete power resistors and switch them into the circuit. Otherwise, a variable power supply could do the trick.

i think im just gonna go water cooling... im tired of buying fans.

[cowanrg]

Originally posted by jbird
How about placing some limitations on the problem? What voltages do you really want the fans to "see"? It may be much cheaper (and easier!) to use some discrete power resistors and switch them into the circuit. Otherwise, a variable power supply could do the trick.

well, i would like it to go from ~5V - ~12V really. there are 2 fans, 5.4 watts each, 0.4A each.

[Warlord2]

I believe a 5watt rheostats with 100ohm should work

seen many people using these for 120mm fans and they say it works fine

[cowanrg]

yeah, i went to radioshack last night (2 different ones actually), and they had jack for potentiometers! they had 2 audios, a couple linears in the 10K-100K range, and that's about it.

know anywhere other than radioshack's website to get them?

frankly, after all this, i think im just going to hook the fans up at 7volts, and forget about all this ;-) ill probably end up running the fans at 7v anyway.

[jbird]

If you parallel both fans, and you want to go from 5V to 12V in 1V increments, you will require 7 resistors and a 7-position wafer switch. (If you run both fans separately, double the above. Also, you can get wafer switches that can switch both circuits simultaneously.) Of course you could go with bigger voltage steps and reduce the parts count. Getting a continuously variable voltage from 5V to 12V is a lot more difficult. Barring a great deal of design, you will require a SEPEC (or CUK) converter (12V input to 5_12V output). Linear Technology and Maxim both sell SMPS chips that will do the trick. Check out their web sites (try a search using SEPEC) - you should find some application notes on how to design and build a suitable converter. (Beware, though, it isn't for the faint of heart!)

[Warlord2]

http://www.jameco.com/ carries thim

[Dissolved]

heh, you guys should go water cooling.. by the time u buy all these parts and fans, u could have gotten a nice water cooling setup.. thats the way im going pretty soon :)

[Warlord2]

I am watercooling but its still very loud if you go 12v on your radiators......

Im at 7v and all I can here is my pump vibrating

[Dissolved]

Originally posted by Warlord2
I am watercooling but its still very loud if you go 12v on your radiators......

Im at 7v and all I can here is my pump vibrating

you have water cooling, and you've only gained 300mhz?

[cowanrg]

you are aircooling and you only get 70mhz?

[Warlord2]

lol

Im at 1.2 because of this ****ing cheap deer psu that is giving me a headace:(


and for the love of god I got the AK31 1.4v so I can do anything with and the hard drive is dieing and I dont want to speed up the process

next thing to buy is new mobo,psu,hard drive,nice memory:D

but yea I was at 1.5 for a while but I couldnt go any higher sense the mobo will only go to 1.89v
Im sure I could get it to 1.6 easly if I have the right stuff

[cowanrg]

300 extra mhz aint bad at all. i wish i could get 300 extra out of mine! we will just have to see... watercooling in like 3 days.

[Nforcer]

ive got a 120mm Sunon 108CFM fan and ive tried wiring it direct for 7v and cant get it to turn

im using it on my heater core - in a water station setup

it is running on a AT psu.........thats all the psu has to run - is the fan

no luck at 7v

at least at 5v it tries to turn over - at 7v it doesnt do anything

what am i doing wrong??

[cack01]

I have the same problem with my 120 sunon fan. I'm looking into getting a pot or a resistor, but now I"m just confused.

[Nforcer]

originally i tried wiring it to a switch (SPDT)

would run at full speed - off in the off pos - and off in the low (7v) pos

so now i dont know what to do

when i wire it to 5v it tries to turn - at 7v - i get nothing

and at 12 - well it works

im going to try a DPDT switch and see if that helps (thats what all the rheobus' use)

ARG

[ciz28]

try keeping the positive lead of the fan on 12v and have the spdt switch go from ground (12v) or 5v (7v). this should give you the 12v/off/7v you are looking for.