WTF is wrong with my stir plate?

[HarvInSTL]

I am about to mount my fan into my project box and I figured I'd test it out. Well all the stir bar does is bounce around. Doesn't matter if it is 1", 1.5" or a 2". Same results. I have made sure that I have one with North up and one with South up.

Ideas?

[ame="http://www.youtube.com/watch?v=_yP_VzF-0lI"]12second video[/ame]

 

[JimC]

Holding it to far from the fan, or not level, or not in the same spot would be my guess.

 

[Drunkensatyr]

Looks like it is starting off TOOOOOO fast, need to start is slower then increase the speed. Mine did that until I put a rheostat on it

 

[HarvInSTL]

Right now I am using one of these to control the fan speed. And that video was with it at the lowest setting so I'm assuming that means 5volts. I am currently testing this with a computer and the fan controller is connected to the motherboard header. I do have a couple 5.4-5.9volt phone chargers that I was planning on using, but does that mean that I can't use them with this fan controller? I don't want to hack up a phone charger unless I'm sure it would work.

http://www.endpcnoise.com/cgi-bin/e/std/sku=fanmate2

 

[pjj2ba]

Looks like it is starting off TOOOOOO fast, need to start is slower then increase the speed. Mine did that until I put a rheostat on it

Bingo! If no rheostat is handy, I have a vague recollection about plastic interupting the magnetic lines of force, so a thick enough plastic sheet may tone down force. I'm talking 1/2" thick or more

 

[Monster Mash]

You really need to mount it in a box before you can really test it.

 

[Funkenjaeger]

Try starting with the fan off - get the stir bar in position before you start the fan. I haven't played with my stir plate very much, but I'm using a glass jar without a perfectly flat bottom, and I have to do it this way or it does the same thing as in your video. Also, I imagine putting it in a box so you're sure the flask is level will help quite a bit.

One thing you should take into account is that the fan is going to spin more slowly when it's properly spinning the stir bar, because of the added resistance of the stir bar in the water - even if you're using a speed controller to slow the fan down to what should be a suitable speed with the stir bar, if you let the fan spin up fully before putting the stir bar in place it can be spinning a lot faster than you want.

 

[knarfks]

Like other people said, you have to have a flat surface for the beaker to set on. Also you have to start the fan off slow with the stir bar already in position. I had to buy a rheostat to cut down a 3.7 volt charger for a 120mm fan so it wouldn't be too fast. It will spin a vortex from top to bottom of a 1 gallon jug.

BTW the rheostat has to be at least 3 watts, but they are $3 at radioshack.

here is a ghetto, but multiuse solution for a box I got from someone else's idea, the box works perfect for a 120mm fan.

here is what a 3.7 volt charger can do

 

[D2T]

I did the same thing you are doing when I was first building mine. The flask/stir bar need to be in position before the fan starts moving, and it helps if you have a rheostat to slowly get it up to speed.