Sciencemadness Discussion Board

Cheap hotplate stiring problems

Chemgineer - 21-1-2022 at 05:09

I bought a cheap ANZESER SH-2 Magnetic Stirrer Hot Plate (very common on Amazon).

After boiling a solution to dryness I noticed on next use that my stir bar struggled to stay coupled to the stirring.

I took the hotplate apart and after checking various things I eventually noticed the neodymium magnets were only quite weakly magnetic. I am guessing they have been heated above their Curie temperature.

I've bought some more magnets to fix the issue but guess this will happen again with this hotplate.

I've also bought a second hand HEIDOLPH MR3001K hotplate hoping this will perform much better.

Is this a common problem with hotplates?

Antigua - 21-1-2022 at 05:18

From experience I can tell you that your Heidolph will serve you for years if you treat it well. It's a great hotplate.
Decoupling happens often when the stirbar's "stirpoint" (the axis around which the stirbar spins) isn't centered on the stirbar. Then one part of the stirbar is longer and the other one is shorter and it leads to it flying all over your flask. The same applies to the internal plate magnets. So this may be an issue with either or both.
Also, don't boil to dryness!