Help with my Stir Plate

[Shanethebarber]

Hello everyone, I was just getting ready to put my stirplate together and I wanted to test it. I have your typical project box with 12 v fan, rocker switch, and rheostat. When I plugged the power in I flipped the switch and the fan started no prob I decreased the power and all of a sudden the rheostat started glowing and smoking. My question is I guess will placing the load and ground on the wrong prongs affect it? I also had zinc washers to give me the spacing I want. I do not posses a lot of knowledge in this field although I am pretty handy, so I apologize if this is a stupid question.

 

[wit2003]

What are the ratings for the rheostat?

 

[Jayhem]

How are you powering the fan? Are you using a low voltage AC adapter (5-12VAC)? I power my fan with a 5.5V cell phone charger and it runs at a perfect speed, I don't even need a rheostat.

 

[stubbydoug]

Also what volts are you putting into the rheostat? I had a 12V power supply going into mine the first time around and it got super hot. It also spun the fan too fast which made the stir piece keep flying off to the side. I changed my power supply to a 5V old phone charger and that slowed the fan down enough to not throw spinner. It cooled off the rheostat too.

 

[Shanethebarber]

The rheostat is 25 ohm 3 watt. I do believe my power supply is way to big at 12 volts 17 watts. I have a ton of cell phone chargers at home that I am going to man handle as soon as I walk in the door. Thank you guys, I am more than sure the power supply is the problem.

 

[Shanethebarber]

Yep! The power supplly was way to big. I wired a new rheostat, and cell phone charger into it and it is working great! Thaks again!

 

[WiggStout1]

The best power supply I've used is the adjustable voltage type and mines operat best at about 7v. I was thinking of beefing up my magnets to see if I can get a more vigorous stir but don't think it's needed. I've had no problems so far. What type of magnets do u use.

 

[Jayhem]

The best power supply I've used is the adjustable voltage type and mines operat best at about 7v. I was thinking of beefing up my magnets to see if I can get a more vigorous stir but don't think it's needed. I've had no problems so far. What type of magnets do u use.

A stronger magnet won't increase your stir rate since the stir bar follows the exact speed of the magnets so a faster fan speed is the only way to increase stir speed.

 

[losMythos]

I find dealing wit D/C is a pain. I did a cigar box type but I used a A/C fan and a ceiling fan rheostat super easy. Glued magnets to the center of fan at the right spacing works great.

 

[CB_in_Tokyo]

A stronger magnet won't increase your stir rate since the stir bar follows the exact speed of the magnets so a faster fan speed is the only way to increase stir speed.

I think he means that with a stronger magnet, the stir bar won't be thrown as easily when he goes to higher speeds.

 

[Shanethebarber]

I used niced sized neo mags from a hard drive. I think I am going to swap out the power supply. I am obviously not going to use a size that will fry things but I'm thinking I'm gonna go 10v. I 'm not happy with the vortex in my flask 12 hrs after the initial start.

 

[stubbydoug]

The way I rigged my my magnets was to glue a large steel washer to the face of the fan. Then I just stuck two of the little round neomidium magnets to that washer. I can send you a series of pictures off line if you'd like. I'm new to the forum and am not real sure how to post a pic into my reply.

 

[dtwhite]

I would like to point out that computer fans are designed to run at 12V DC, but each fan is different in regards to what RPM it puts out at that rating. Basically, just because your fan works fine at 5V doesn't mean it's a good voltage for all fans. Mine, for instance, was a low RPM fan to begin with so 5V was incredibly slow and it barely started up. 12V could be insanely fast for other fans such that no reasonably strong magnet could hold a stir bar, too. Just depends on the fan.