Trying to build a stir plate, magnet slows fan down

I have a rather large fan that runs fine connected to the 12v 2a power supply but when I put the magnet on it it barely moves (maybe 1-2 rotations per second) and sometimes stops entirely.

I haven't seen this mentioned in any of the stir plate howto's, is it a specific type of fan? It seems like the magnet might be interfering with the motor, how does everyone else's seem to work?

Do you have anything between the fan and the magnet? Or is the magnet right on top of the motor coil for the fan ?

I built my stir plate and I think you are dealing with 2 possibilities.

1: You need a "barrier" between the fan and the magnet. I used a thick fender washer. I glued the washer to the fan with 2 ton epoxy and the magnets to the washer with the same. I spun the fan by hand to be sure I had it centered, same with the magnets.

2: use a different fan. Some fans just work better than others from what I have read.

hope this helps! GL!

What kind of bearing is the fan, what kind of fan in general? Some fans have magnetic bearings, they sort of 'levitate' to cut down on resistance and friction. I could imagine a stir bar with a strong magnet interfering with this field and creating a problem. Do a search online for your fan at an online store, look at the specs and see what type of bearing it uses.

Thanks, I put the magnet directly on the fan just like this picture:
http://www.donosborn.com/homebrew/stir_plate_13.jpg

I have no idea what kind of fan it is, it came out of my computer case but the behavior also happens on another fan I have.

I'm using a magnet out of an old harddrive so it looks exactly like the picture above. I'll try the washer thing when I get home today.

IrregularPulse said:

Do you have anything between the fan and the magnet? Or is the magnet right on top of the motor coil for the fan ?

Click to expand...

You need a metal barrier between the magnet and the fan coil, or it will mess with the magnetic field of the motor. The fender washer is a good idea. I used some random metal bracket I had.

haze

I had the same problem and got around it by putting a flat piece of plastic between the fan and the magnet. No glue needed. The magnet holds the plastic in place.