potentiometer help

Hi all. I know nothing about electricity , but followed the Brew mag build you own stirplate article. I wired in a potentiometer and it works, but it smokes a little, so I think I have something wrong. Here are the specs, maybe someone can see what I did wrong:
Fan - 12 volt, 0.10A computer fan
Power Supply - 120 VAC, 60 Hz, 50 mA, 3.7 VDC cell phone charger
Potentiometer-5 kohm linear taper, 500 VDC, 0.5 W

Is this the wrong potentiometer? Someone told me that based on the VDC of the power supply, that I could use a household dimmer switch in place of the potentiometer. Is this true?
I'm clueless! Thanks

Could you post the specs of the rheostat too? They are perhaps the most important. I would suspect that you may somehow be surpassing its wattage rating.

But right off the bat I can tell you that your power supply is way under spec, and won't get most fans spinning. Find yourself a 9, 6, or at worst a 5V PS and then we can talk business .

Be careful with the blue smoke from your components; once it gets out it's really hard to get it back in .

Yeah you're severely under powering the rig. Your specs right there indicate your power supply is providing 0.05 Amps, but your fan requires 0.10 Amps even if it was directly wired. I agree about the smoke, you probably fried it and will need to get new components.

Check out this thread for some diagrams on how it should work with a potentiometer. I think you can either use a potentiometer or a rheostat, not necessarily both. I built mine by following the instructions in that link, but first tried to take some shortcuts on some components I didn't think were necessary. It didn't work. Then I went and bought the exact components listed (all the resistors and everything - VERY important) and wired it up EXACTLY as diagrammed, and it worked perfectly. It turns out there's a lot of math and stuff going on that us normal folks don't understand, so we have to follow the instructions to the T. For example, I learned later that the amount of power being supplied to the fan has to do with the rating of the potentiometer divided by the rating of the resistor that connects the potentiometer out to the voltage regulator out (R2/R1 in the first diagram in the linked thread). I also tried mine with both a 12V and a 6V power supply, and it worked much better with the 12V. The 6V had trouble getting the fan to start spinning when a flask and stir bar was on top.

I would highly recommend starting over and following the instructions in that link thread. It's worked for quite a few of us. Good luck!

I don't have a rheostat. I didn't know I needed one.

I'm rather surprised that dinky little power supply is enough to spin that fan. How do you have it wired up? I don't have that BYO article to refer to.

A household dimmer won't help you, those are a completely different design that only work on AC, it won't do you any good with DC.

Yeah, your power supply is way too small. Look for a 500ma or above rating for the current, and get a 12V model, so you will have almost the whole range of the fan to work with (the pot will drop a little voltage - they are very ineffieient).

Checkout this site, and scroll down to where it beging "Potentiometers find their most sophisticated application as voltage dividers,..."

That section describes what you want to do as far as wiring goes. Replace the battery with your PS, and the motor with your fan.



If you want to build a more efficient and precise spinner, you will need to use a power transistor and regulate the gate current with the pot. I have plans for this somewhere - it's what I use on my computer fans. If you may want to do it that way PM me.

Thank you all for your input. I believe I am now edgemakated.