weak stir plate

So I followed a DIY stirplate process, got a stir bar, then smiled thinking that I now have an awesome stirplate for under $50. I used a computer fan, just as many people have. When I put the bar in the flask either the bar stopped the fan from rotating (too strong of a magnetic connection) or the bar just wiggled and didn't spin. I think my fan is too weak! Ahh! Anyone else run into this?

Some fans have the magnetic material too close to the face of the fan and the computer magnet's magnetic flux is killed or canceled by the computer magnet which is much stronger. You can try another fan or make a spacer from wood about 1 inch away from the face of the fan and glue the magnet to the wood. You have to be careful to balance the weight so it does not wobble. If balance is good the fan will spin full speed. When you mount your fan the magnet has to be close to the flask bottom or you will not have good magnetic coupling with the stir bar. I found that a 1 inch stir bar works best because it is about the same length as a computer hard drive magnet. For larger stir bars you need a longer magnet the same length to work well. tip: I try to mock up the fan and the flask with a plastic sheet over the fan to see how close to mount the fan. I then mount the fan in the case with the same spacing so I know it will work the first time.

Could be a power supply problem if it's not the correct voltage. You also have to start the fan slowly so it grabs the bar and then crank it up. If you don't have a rheostat or potentiometer then use your finger to control the fan speed for a test.

It also could be a magnet polarity issue. I just ordered my stir bar but I think they are made of 2 opposing magnets sealed in some sort of casing. That means the 2 magnets attached to the fan need to be opposite polarity facing up. With the fan off, touch your stir bar tip to the magnets until it attract and make sure the other side attracts to the other magnet. Both sides of the stir bar should attract to each of the magnets.

I followed the directions and used 2 magnets, that setup did not work for me. When I switched to just putting 1 HD magnet in the center of the fan it worked with a 1" stir bar for me. I bought a 4 pack of stir bars in different lengths from 1-2.5" and the 1" bar is the only one that works on my setup but it stirs 2 liters of liquid with vortex. The other stir bars shake a while then get thrown off to the side.

Yunus said:

I followed the directions and used 2 magnets, that setup did not work for me. When I switched to just putting 1 HD magnet in the center of the fan it worked with a 1" stir bar for me. I bought a 4 pack of stir bars in different lengths from 1-2.5" and the 1" bar is the only one that works on my setup but it stirs 2 liters of liquid with vortex. The other stir bars shake a while then get thrown off to the side.

Click to expand...

I said the following in this thread "I found that a 1 inch stir bar works best because it is about the same length as a computer hard drive magnet. For larger stir bars you need a longer magnet the same length to work well. tip: I try to mock up the fan and the flask with a plastic sheet over the fan to see how close to mount the fan. I then mount the fan in the case with the same spacing so I know it will work the first time. "

Check out my build in my signature... There is a lot of trouble shooting discussion after my "DIY" post.