View Full Version : Potentiometer Problem

10-08-2002, 12:55 PM
last weekend i built (rebuilt) my rheostat fan controller thingy :)
the last time i built it with like 2 watt potentiometers and it caught fire, i was wonderin if any 1 knows what watt potentiometers i should use to prevent it from bursting into flames

any help would be........um... helpful:cool:

10-08-2002, 01:24 PM
According to this thread (http://forums.procooling.com/vbb/showthread.php?s=&threadid=4295) it should be rated for at least 1/4 of the total wattage that is applied to it.

Since you've got concrete experience, maybe you can tell us all about what you tried to load on it?

10-08-2002, 01:58 PM
ok, heres my setup, i had 3 pots. each pot was running 1 fan. there were two 120mm fans and one 80mm fan

10-08-2002, 02:12 PM
Something is fishy...

Are you sure your pots were rated for 1K Ohm, 2 Watts?

10-08-2002, 02:25 PM
mine are either 1 or .5 watt pots
its all they had a radio shack :(

10-08-2002, 02:34 PM
If the pot you have is that one with the 1 1/2 inch long shanck, it's 1/2 (0.5) watts.

What's the power rating of your fans? (volts and amps, if not watts)

10-08-2002, 02:53 PM
my pots aren't those long ones, my pots are about 1.5 inches total. one of my 120mms says that its 2.8 watts, but the other fans say nothing about electrical specs except that they are 12volt fans

10-08-2002, 03:26 PM
also, on my pots i connected the fans positive to the right prong, the negative to the center, and a positive power line to the other prong. the pots actually controled the voltage but is this wiring incorrect??

10-08-2002, 07:42 PM
That would do it...:rolleyes:

You want to use the right and middle pins of the pot, to tap into the 5V (or 12V) connection to the fan. Ground from PSU goes to ground (negative) of fan, nothing else.

10-08-2002, 09:43 PM
HOLY SOLDERING ERROr BATMAN!!!!!!!!!!!!!!!!!:eek:

Thanks a WHOLE lot Ben, the things don't even get hot now!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
im sooooooooooooooooooooooooooooooooooooooo friiiiiiiiiiiiiiiiiiiiiiigiiiiiiiiiiiiiiiiiiiiiiii iiiiiiiiiiiiiin happeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeeeeee!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!

phew..................ok i'm done now thanks Ben

10-08-2002, 09:55 PM
1 problem is that now, even though the pot doesnt get very hot, it doesnt control the fan as effectively IE when the pot is at full power the fan is at full power but when i turn the pot all the way down, the fan only lowers slightly in speed are the pots still the problem???

Can O' Beans
10-09-2002, 01:19 AM
They might just not be high enough in resistance to slow the fan down much. What is their resistance?

10-09-2002, 10:17 AM
You really need to know what resistance is needed. Also, watch out for linear versus audio pots: the resistance changes linearly in the former, and that's what you want.

10-09-2002, 02:47 PM
the resistance on the pots is probably 100ohm but i dont know how high it goes, i think i'll just spring the 5$$ or so for some new ones, just tell me what i should get

10-09-2002, 03:06 PM

First off, if one of your fans is rated for 2.8 Watts, you'll need a pot rated for at least 0.7 Watts. The closest one you'll find, I believe is 1 Watt.

If the same fan is rated 2.8W at 12V, then its (average) resistance is about 53 Ohms. A 100 Ohm pot would, at best, leave 4 volts for the fan, which is just below the minimum voltage, so that'll work.

In short: get 100 Ohm, 1 Watt, LINEAR pots.

If you need sources, I've got a few links.

10-22-2002, 11:43 AM
Ok, took a trip to Radio shack last week and along with other stuff, i bought sum pots, soldered evrythin together and it works perfectly. I can now turn my 120's down to a whisper and still feel the wind on my desk :D

10-22-2002, 11:54 AM

10-22-2002, 12:30 PM
Heres a pic! :cool:

01-06-2003, 12:19 AM
i was under the impression that the pots have to be rated a higher wattage then the fans OTHERWISE IT WILL BURN!!!!!

unless you have a voltage regulator, then i dont know.

here is a formula to calculate the wattage you need for a fan

Watts=volts X amps
ex. w= 12v x 0.2(120ma)