Potentiometers, trimmers, chokes... agh! I'm confused!

[Crazy Jayhawk]

I'm trying to figure out just what these things are. Do potentiometers perform the same function as rheostats? And what are these things called trimmer pots? Chokes I think I understand, but even that's debatable. :confused:

Thanks for your help. :)

[eobard]

They're all basically the same thing, variable resistors, the reason there are so many names is it helps some people feel big, using jargon.

[flounder43]

I found this while looking through Google, it doesn't make much sense to me:

http://www.clarostat.com/NewWebsite/website.nsf/SiteMap/BBE4A85541BE7B51872568B20011F3BC?OpenDocument

look a the bottom, there is an explanation.

I would also refer you to my personal experience, located in this thread: http://forums.overclockers.ws/vb/showthread.php?s=&threadid=43783

[donny_paycheck]

Rheostats vary voltage because they are inductive loads, potentiometers vary current because they are resistive loads. Basically this means that a Rheostat lowers the voltage applied to the fan by absorbing some of it and dissipating it as heat, while a pot varies the amount of current flowing through it by increasing the resistance of the fan circuit. Rheostats are used as light dimmers and pots are used as volume controls. A rheostat is less effecient because it absorbs rather than resists current flow, plus it will get hotter but because it varies voltage it is better for a speed control application. You want the ultimate? Use a LM317 voltage regulator IC and the +12 and -5vdc power supply rails to put in 17 volts.....then the IC can regulate the voltage between 0 and 15 volts with little current loss and great effeciency.

[Owenator]

Originally posted by
Rheostats vary voltage because they are inductive loads, potentiometers vary current because they are resistive loads. Basically this means that a Rheostat lowers the voltage applied to the fan by absorbing some of it and dissipating it as heat, while a pot varies the amount of current flowing through it by increasing the resistance of the fan circuit. Rheostats are used as light dimmers and pots are used as volume controls. A rheostat is less effecient because it absorbs rather than resists current flow, plus it will get hotter but because it varies voltage it is better for a speed control application. You want the ultimate? Use a LM317 voltage regulator IC and the +12 and -5vdc power supply rails to put in 17 volts.....then the IC can regulate the voltage between 0 and 15 volts with little current loss and great effeciency.

donny_paycheck,

OK so how would you wire this? Is the +12V the input and the -5V the ground? I am building a new/cleaner LM317 based volatage regulator this weekend so any info would be greatly appreciated!

O

Here is the ciruit I'm building.

[Crazy Jayhawk]

Originally posted by Owenator


donny_paycheck,

OK so how would you wire this? Is the +12V the input and the -5V the ground? I am building a new/cleaner LM317 based volatage regulator this weekend so any info would be greatly appreciated!

O

Here is the ciruit I'm building. I tried building that circuit, but something went wrong. Either I got a bad LM317 or I've shorted something out somewhere because no matter what I do, the fan doesn't turn.

[donny_paycheck]

You could try using a LM317K vs. a T, the K is in a TO-3 case and can handle 3 amps vice 1.5. You could try substituting a lower value pot on the +ADJ leg of the IC and using a resistor in series with it to make sure you don't over-bias the IC too much also....for the 17VDC in use the +12 rail as normal and use the -5 rail as the ground side. The LM317 needs at least 15VDC to function properly, although I'm surprised it does nothing at 12. Hope this helps...

[KILLorBE]

Originally posted by donny_paycheck
You want the ultimate? Use a LM317 voltage regulator
The Ultimate would be a MIC29302BT high current (3A) low drop-out regulator, 0.5V drop Max. (probably more like 0.3-0.37V according to the data sheet) VS 1.5-2V for a LM317.although I'm surprised it does nothing at 12
Strange it should work fine, tho the output would be ~10.5V max.
Originally posted by Crazy Jayhawk
I tried building that circuit, but something went wrong. Either I got a bad LM317 or I've shorted something out somewhere because no matter what I do, the fan doesn't turn.
Are you sure you used the right legs? Or did you burn it when you soldered it? (If you look @ the front of a LM317 the left leg is Adjust the middle leg Vout and the right leg Vin)

Owenator this is what I would do (see pic) I added R3 (680 Ohm) so the fan wont stop when you 'accidently' turn the pot down completely (If you turn down the pot completely there will still be ~5V on the output).
The lower value pot (2K) gives you a bit better control, (a 1K pot might even work better, haven't tried it (yet) tho).

**EDIT** new pic (NOT somehow it still showed the old pic--> see new post for pic)

[KILLorBE]

Originally posted by Crazy Jayhawk
And what are these things called trimmer pots?

Trimmer pots are (usually) used for 'one time only' (fine tuning) adjustments, the yellow ones are precision trimmers the black ones are regular trimmers.

[jbird]

Trimmer pots are small, low power (i.e. voltage/current) 3-terminal variable resistance devices. Pots is short for potentiometer. The difference between a pot and a rheostat isn't much - a pot has three terminals, and a rheostat has only two. You can convert to a rheostat by shorting one of the end legs to the center (wiper) leg; a rheostat cannot be converted to a pot. As for "chokes" - that is an old term for inductors. Early radio builders called them that because they were used to isolate or "choke off" high(er) frequencies, particularly in power supplies and busses. Hope this helps!

:cool:

[Crazy Jayhawk]

Originally posted by KILLorBE
Are you sure you used the right legs? Or did you burn it when you soldered it? (If you look @ the front of a LM317 the left leg is Adjust the middle leg Vout and the right leg Vin)Turns out I had V-out and Adjust switched. Switched them around and now it works fine.

[KILLorBE]

Originally posted by KILLorBE

The Ultimate would be a MIC29302BT

Mmmm I've been to my local electronics shop today and asked if they had them and what they would cost *cough* ~10 times as much as a LM317 :eek: (~$14)

Here's the new pic :)

[YMAN]

C2 is an Electrolytic Capacitor
Because it has the +

C1 is a Ceramic Capacitor,
Am I correct?

I always get the 2 mixed up! :D

-------------------------------------

You guys know anything about power supplies?
http://forums.overclockers.ws/vb/showthread.php?s=&threadid=44360
I could really use you help

[donny_paycheck]

Originally posted by YMAN
C2 is an Electrolytic Capacitor
Because it has the +

C1 is a Ceramic Capacitor,
Am I correct?

I always get the 2 mixed up!

Correctamundo/