A tale of two magnets.

A project log for P1 - Aquarium to vacuum pump conversion

The now classic conversion of an aquarium pump, and what you probably shouldn't do too..

Daren SchwenkeDaren Schwenke 02/04/2018 at 04:460 Comments

The original ceramic magnets in the pump were decent as far as ceramic magnets go, but they were not even close to the pull of the N42 Neodymium magnets I had.  

I could actually completely overwhelm the ceramic magnets and stick the neo magnets right to them in any orientation.  This led to just trying to augment the existing magnets by sticking the neo one to the back.  No significant change, so I opted to try to replace one of them.

I drilled out the brass rivet and then the glue still holding it on was easily split with a well placed screwdriver twist.

I then proceeded to glue a 12mm disc magnet I had to the arm.. several times.

Gluing Neodymium magnets is actually kinda tricky.  Epoxy doesn't stick very well, and superglue isn't strong enough on it's own unless you have two perfect mating surfaces.  So I used both.  That worked for a while, but eventually failed under the duress of a small impact event.   The third try had me grinding off the positioning tabs, wet sanding the steel for a perfectly flat surface, super-gluing to that, and then bridging the back/around the sides with a generous amount of UV cure resin.  Thankfully, that has held up.

The 12mm magnet did not work... at all.  The field lines were too concentrated and so as soon as it swung to one side it stayed there.  The electromagnet just wasn't strong enough to push it away.

So that got replaced with a larger 18mm magnet.  That is actually about 5mm larger than the ceramic one I removed.

That worked, I believe because it was large enough to pull on both sides of the electromagnet evenly.  It still tended to want to stay deflected when I capped off the vacuum though and so performance was not very good at all.  That turned out to be fixable though.  More to come..