removing a Thermistor and replacing with a Pot

[Adragontattoo]

ok so I picked up a few of http://www.coolerguys.com/840556050001.html awhile ago and I want to mod 2 of them to have a Pot instead of the Thermistor. What size pot do I need to use(going on a couple Delta 120's)? Also does the thermistor have any current running through it to tell me which is the positive and which is the negative side or does it even matter?

Eventually Ill build my own Fan controller but for now I dont have enough knowledge or faith to build my own and trust it.

[four4875]

can you measure the resistance across the thermistor? then you get somethin that is a tad higher than that (giveit full range like) and i think you should be set. and i dont think polarity matters.

[Adragontattoo]

I should be able to get it measured, Ill have to check when I get home to see what happens.

I may just use one as a "please dont break on me" tester and see what happens with the Pots I have at home (250k I think) and then a fan or two will be connected (low power 80's).. these will be connected to the tester PSU (old antec 300w) to see what happens.

[four4875]

i think the 250k would definately do the job. basically im thinkin that 0ohms will be full speed, and higher will be lower, up to a certain point. basically, with the vr varying so much, it'll justbe toucher i think. but it should definately cover it i'dthink.

[Adragontattoo]

ok so it is a 25ohm pot. It isnt giving any effect when it is turned.. The only thing I can think is that it is too low and not giving enough resistance. I am going to run back to radio shack and exchange it for a higher resistance one to see what happens.

[Adragontattoo]

ok got it working


picked up a 50k
100k
1M

the 1m is off/on ONLY
the 100k works but is REALLY picky and is mostly high/low/off
the 50k is closest to correct. The voltage gets too low about halfway through and drops out though. It works pretty well otherwise and once I test mount it I can mark the high/mid/low/off spots if possible.

[four4875]

what about a 25k? if you can get one locally, i'd try how that works.

[Adragontattoo]

I tried the 25k first, it wasnt enough and did nothing.

It seems like it is about 35-40k to about 65 or so on the Thermistor.

[eobard]

Run a fixed resistor inline with the variable one. So if 0-25k is no good put a 33k fixed resistor in line and now you got 33k-58k.

[Adragontattoo]

Argh and something that simple is what I should have thought of... grrr I may just do that and bump the resistance a bit over 50k to see what happens. About half of the Rotation on the Pot does nothing (below about 30 or so, Im guessing here) so I either am going to have some (+/-45%) dead space on the Pot or I am going to be able to bump it up high enough to minimize that amount of dead space.