DIY Stir Plate Question

I'm putting togeather a Stir Plate from many resorces online and here. I did a temporary wire of all the connections before making them permenant. I turn the switch on and the stir plate runs. But it only runs on one speed. I turn the potentiometer and nothing happens. All the wiring is correct. Sometimes I have to give the fan a push to get it going. And to me the fan seems to run too slow. The fan is a 4 x 4 size and 12v I bought at Fry's. Is the fan no good? Or did I miss something.

what is your power supply specs?

Could be a few things. Disclaimer - I am not an electrician, or an engineer, and am in no way qualified to speak on this subject, other tan having built a stir plate, and destroyed a few power sourced and fans in the process.

I too had to spin the fan to get it going a few trys. Is there anything attached to it yet, like washers/magnets?

It could be wired incorrectly (like i said - destroyed a lot of components).

The switch/potentiometer might not be able to pass enough power to turn the fan. I opted for no switch just to get as much amps as possible pushed thru to the fan.

Could you take a picture of your wiring, and include any specs on the switch/ potentiometer?

I am an electrician. I work with schematics. Power supply is 12v. I started off with a 5v cord and found a 9v cord. Then the 12. Yes I have a washer and magnets glued to the fan.

if your wires are hooked up right then it could be a busted pot. does the fan go faster if you connect it directly to power? If so I'd say get a new pot. I assume you used a 1/4w part.

I built mine with a 120mm fan also from Frys, but ended up using a 9v 300ma power supply that I had sitting around. This gave me the best range of speed with the Rat Shack pot. Even though I also tested it out with a 6v 300ma power supply, it did not give me enough speed on my fan to create a vortex to just stir water when testing.

I know that when I built my stir-plate, I had to put multiple washers in between the magnet and the fan. My magnets were strong enough that they stopped the fan from spinning.

Okay. I changed out the fan. I found a smaller fan lying around the house. I think it's like 3". So I connected it to the stir plate and everything works fine now. Rheostat works like it suppose to. Thank you guys n gals. I hope to be brewing my next Pliny batch this Saturday.