DIY Stirrer Mantle

MargaretThatcher · Wed Jun 15, 2005 5:31 am

Been thinking about making an electromagnetic stirrer: no moving magnets, but several electromagnets arranged radially to create a rotating magnetic field. I know there are some commercial stirrers that operate this way. The advantage is no moving parts apart from the stirbar and excellent speed control.

Tesla did original work about creating a rotating magnetic field in a similar way.

2 or 3 phase is the way to go, which would require 2 or 3 pairs of electromagnets. Generating a variable frequency 3 phase supply looks fairly difficult (for a sine wave at least). Maybe square wave would do.

The magnets themselves could use iron wire cores, which max out at nearly a tesla (similar to rare earth magnets).

Guest · Wed Jun 15, 2005 11:40 am

Now that sounds really exciting,

I am interested, as I also want to make one,
So let us know of your progress,

s

bio · Working Bee

...............Generating a variable frequency 3 phase supply looks fairly difficult (for a sine wave at least). Maybe square wave would do. ...................

Not really as nowdays there is a chip for damn near everything. A PLL (Phase Locked Loop)will do it or a three phase PM motor controller chip used for steppers and servos.

Here is some info on a newer PLL with application data.

http://www.national.com/an/AN/AN-210.pdf

A servo type, 3phase permanent magnet motor controller completely assembled would be easiest and square wave is fine for DC or stepped square wave for AC however AC motors don't generate much torque if slowed down very much and therefor are pretty much limited to centrifigal fans and pump applications.

VFD (variable frequencydrive) 3 phase motor drives are readily available but are rather costly and are not available in subfractional horsepowers.

I saw a 6 position one before that could be programmed to 6/3 or 1 position using the same grid. Maybe if you could get ahold of a manual we could see what parts are used as the "brain"

primathon · modified

One of the problems you'll run into when trying to encapsulate a magnet in glass is that the intense heat produced will demagnetize a portion of the magnet (see post

4037

) and leave it slightly unbalanced. I mean, I suppose it's possible to do it fast enough and accurately enough to where you barely touch the magnet at all with the heat, but seems very unlikely. Propane and O2 can reach >5,000°F, the working temperature of pyrex is ~2,275°F, and the curie temperature (point at which all magnetic properties are permanently lost) is 590°F for NdFeB magnets. You gotta be a goddamn ninja to pull that off.

MargaretThatcher · Thu Jun 16, 2005 3:29 am

primathon · modified

Yeah, Alnico magnets rock. I wish I had some Razz

Good thinking on your implementation of that, btw. I'll have to see if I can whip something similar up.

MargaretThatcher · Thu Jun 16, 2005 9:01 pm

I got mine from a hobby electronics shop - used for activating magnetic reed switches.