Ive been searching on and off for a couple of years now to find a source of potentiomenters which are used in comercial fan controllers, to no avail. Through a bit of calculation myself and with the help of others, i keep coming back to the point of needing a 100Ohm pot, which thus far have been impossible to find. Basically i want to take 12V in, and vary it between 12V and 0V, as you would expect with a fan controller. I know that some fans dont repond below a certain voltage, but thats fine, all i want to do is vary the voltage in under one revolution of the knob, but more than about 30 degrees, which is what i had when i last tried this. On that occasion i was sold the "lowest value pot" Maplin stocked, which turned out to be 10k, thus gave almost no controllable variation. Now ive found that RS components do stock 100 Ohm pots here and they're about £5 a piece. They do another one which is £13 ea, but as i need 5 of them, i'm not paying that much. Basically what i need is confirmation that the pot i need is infact 100 Ohm, and if there are better palces to get them in the UK (i have an RS account, so if need be i can get them there). The fans i'm using are Zalman low profile 80mm units designed for use with their large passive heatsinks if more cooling is required. The fans draw 0.14A @12V each and i'll be running them in pairs, to effective drain will be 0.28A. Any help much appreciated.
I would have, in your position, just tied a 100 ohm resistor in parallel to the 10K variable resistor you have. Now you can not go over 100 ohms and can turn down to less than 1 ohm of resistance if you desire.
Most probably use the cheapest they can find that work, and certainly use over 1kOhm. Commercial fan controllers typically do not use the pot to dissipate power, but rather, to control a resistor divider for some IC that does that work. The real trick is cheaply getting an output that can go near 12v, but still be able to handle some decent current/power (growl-inducing PWM is the common method). I=V/R, 0.28A=12v/43Ohm So a 100Ohm pot should get you pretty far down (4v or less). Just be sure it can handle dropping 70% of the power--near 2.5W. Also, it will perform differently with a different fan configuration. 50Ohm or so would probably give better control, for this method (down to just under 6v).
Would this limit it to 100ohms through the whole turn? or just limit the effect to a small portion as before? Thanks Cerb, how would you contstruct something like that, any ideas? (from experience on a few occasions, i suck at anything more than basic circuits)
This will limit the entire apparent resistance to 100 ohms max. The variable resistor at full resistance (wiper on one side): 10k ohms (10,000 * 100) / (10,000 + 100) = 99 Ohms max The variable resistor wiper at the other side (0 * 100) / (0 + 100) = 0 Ohms min
www.cpemma.co.uk It took me quite a few tries to get the LM317T one working, and I got only to 10.4v. The transistor one, with an extra small resistor inline with the pot, would get closer, but then the trouble is finding a single transistor to do the job. Exactly how I would construct it is still somewhat up in the air . (wrong stuff was here. SLEEP) Oh, one idea, which would work up to four channels, and require only minimal soldering work: get a Sunbeam Rheobus, measure the pot values, remove the panel and pots, replace them with your own of the same ratings, wired back to it (so it can be hidden away, not taking a 5.25" bay, with only wires for now-external potentiometers going to it). Still not up to full 12v, but you'll get a good half turn to work with, I think (0-11v or so).
http://www.maplin.co.uk/search.aspx...=y&criteria=Potentiometers&doy=9m10&worldid=3 Yup hteres one here but finding the fixing hardware is a pain in the arse (pun intended)
Are you against using voltage regulators? You could use a low drop out regulator as described here along with a potentiometer with a built in switch. The switch would control the ON/OFF function (enable pin) of the MIC29152 (or similar) regulator. Basically your voltage range would be something like 6.9V-11.9V, along with an OFF position. I've built the circuit on that page and it works great for my 120mm fans. Or you could just do as Cerb said and modify a store bought fan controller to use whatever pots you wanted. While not being quite as flexible it would probably be the easiest route to go.
On all but the lowest power fans a 50-ohm pot would be better, but the problem is finding a wire-wound one in a suitable wattage, around 3W. One of these might be OK. See me for the theory side. All modern commercial controllers use a regulator or PWM circuit with ordinary low-power (1/4W or less) pots.
Thasnk guys, voltage regulators and circuits of that ilk are a tad over my boundaries of ability electronics wise, really looking for the simpleest way at the moment. Those 50ohm units look good cpemma, anything special required to order from that place or to get an account?
Quad LEDs This thread answered ALOT of questions I had about fitting a rheostat/potentiometer. One thing i've thought about is that the fan that i want to fit a rheostat to has 4 blue LEDs built into the fan chassis. It's a 120mm Casecom fan and i was wondering what affect a potentiometer would have. I'm guessing it would fall into these: A: it wouldn't work at all B: fan would work (increase/decrease the RPM) but no lights C: it would dim the lights and increase/decrease the fan RPM D: It would kill the fan Any information woudl be great!
At best the fan will slow down and the LEDs will dim slightly. If they've connected a few blue LEDs in series (so it takes more voltage to light the string) it may even dim the LEDs to extinction at low speed settings. But it won't damage the fan and you'll have speed control.
hmm. The LEDs are connected through metal strips inside the plastic case that run around the edge of the fan chassis. I wonder if there's any way of jsut having the fan connected to the potentiometer and both connected to the rocker switch i intend to use.
If you do a search in the the Modding forum, maybe Mod Guides, I remember people showing how they'd modded fans to separate motor power from LED power. But I'd try the fan first, may look OK.
Ok, i've made my first sketchup of the housing and rheostat. all looks fine. Used a grill compnonent and a fan component. I'll make a project log shortly edit: read the project rules, won't do it until i'm in the middle
