Magnetic Stir Bar, Large

I may have received a damaged unit, but the one I received had two magnets inside and thus was a waste of $9.95 +S/H.

In order for a stir plate magnet to work it must be one magnet, with only one north/south magnetic field. Like this

N--------S

If the stir bar has more that one magnet, it will have two field, like this.

N-----SN-----S

This is the magnet I received. Since the stir bar had two fields it was unable to center on the stir plate. The stir plate magnet will grab onto one end and spin the magnet off center until centrifugal force cause it to spin off the stir plate magnet.

I agree with the previous review that this doesn't work. But not for the reason he suspects. The magnet does not have two fields as he suspects. Even it there were two magnets, as long as they are aligned north to south, it will act as one field. The problem is that in order to work, the magnet inside of the stirrer base has to be the same length as the stirrer bar. Since most stirrers use a 1" magnet, they have a 1" internal magnet. I took mine apart to confirm this. With a 2" stirrer over an 1" internal magnet, on pole of the longer magnet aligns with one end of the shorted internal magnet. The other end then overhangs the internal magnet by one inch and is therefore off center. When the stirrer starts, the long stirrer bar spins off center and flies to the side of the flask. It would work if you modify the internal magnet(s) to 2" spacing but probably not worth the effort as the 1" works fine.

Don't know if this is a result of my shoddy homemade stir plate or this stir bar but I didn't have much luck with this guy. It spun off more often than I liked making it uncomfortable to use when I am wondering if it is going to work. I bought another one with the ridge in the middle and had more luck.