Potentiometer Problem

Vector86 · 10-08-2002, 11:55 AM

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

bigben2k · 10-08-2002, 12:24 PM

According to this thread 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?

Vector86 · 10-08-2002, 12:58 PM

ok, heres my setup, i had 3 pots. each pot was running 1 fan. there were two 120mm fans and one 80mm fan

bigben2k · 10-08-2002, 01:12 PM

Something is fishy...

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

Vector86 · 10-08-2002, 01:25 PM

mine are either 1 or .5 watt pots
its all they had a radio shack

bigben2k · 10-08-2002, 01:34 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)

Vector86 · 10-08-2002, 01:53 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

Vector86 · 10-08-2002, 02:26 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??

bigben2k · 10-08-2002, 06:42 PM

That would do it...

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.

Vector86 · 10-08-2002, 08:43 PM

HOLY SOLDERING ERROr BATMAN!!!!!!!!!!!!!!!!!

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

Vector86 · 10-08-2002, 08:55 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, 12:19 AM

They might just not be high enough in resistance to slow the fan down much. What is their resistance?

bigben2k · 10-09-2002, 09:17 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.

Vector86 · 10-09-2002, 01:47 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

bigben2k · 10-09-2002, 02:06 PM

OK.

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.

Vector86 · 10-22-2002, 10:43 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

bigben2k · 10-22-2002, 10:54 AM

Kewl

Vector86 · 10-22-2002, 11:30 AM

Heres a pic!

lukasz70 · 01-05-2003, 11:19 PM

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)
=2.4watts

10-08-2002, 11:55 AM	#1
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	Potentiometer Problem 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

10-08-2002, 12:24 PM	#2
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	According to this thread 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? __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

10-08-2002, 01:12 PM	#4
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Something is fishy... Are you sure your pots were rated for 1K Ohm, 2 Watts? __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

10-08-2002, 01:34 PM	#6
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	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) __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

10-08-2002, 06:42 PM	#9
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	That would do it... 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. __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

10-08-2002, 12:58 PM	#3
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	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, 01:25 PM	#5
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	mine are either 1 or .5 watt pots its all they had a radio shack

10-08-2002, 01:53 PM	#7
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	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, 02:26 PM	#8
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	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, 08:43 PM	#10
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	HOLY SOLDERING ERROr BATMAN!!!!!!!!!!!!!!!!! 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, 08:55 PM	#11
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	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???

10-09-2002, 12:19 AM	#12
Can O' Beans Cooling Savant Join Date: Aug 2002 Location: Pa - USA Posts: 264	They might just not be high enough in resistance to slow the fan down much. What is their resistance?

10-09-2002, 09:17 AM	#13
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	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. __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

10-09-2002, 01:47 PM	#14
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	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, 02:06 PM	#15
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	OK. 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. __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

10-22-2002, 10:43 AM	#16
Vector86 Cooling Savant Join Date: Jun 2002 Location: KANSAS "it's not just cows"! Posts: 211	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

10-22-2002, 10:54 AM	#17
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Kewl __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

01-05-2003, 11:19 PM	#19
lukasz70 Cooling Savant Join Date: Nov 2002 Location: Ontario. Canada Posts: 159	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) =2.4watts __________________ Asus A7V266, AMD1600xp 1x 256ddr 2100 Crucial radeon 8500 64mb, Ati TV-Wonder PCI Maxtor Diamond Max Plus 9 7200rpm ata133 & 60 MAXTOR ata100@5400rpm 6xdvd, TDK dvd+RW SoundBlaster 5.1 w/ logitech Xtrusio DSR100 speakers Case: Enlight 7237

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