Stir Plate Magnet Size Question?

[fur_252]

Building a stir plate came across rare earth magnet 3/16 size at radio shack are two of these magnets going to do the trick for 2000ml starter? Or of all else could 4 of them side by side work? If that wouldn't work what size of rare earth magnet would work?

 

[fur_252]

Building a stir plate came across rare earth magnet 3/16 size at radio shack are two of these magnets going to do the trick for 2000ml starter? Or of all else could 4 of them side by side work? If that wouldn't work what size of rare earth magnet would work?

Bump

 

[day_trippr]

3/16" diameter - or thickness? If that's the diameter, they may work ok, but I'd be tempted to give them a pass and look for larger button magnets.

Otherwise, a pair of neodymium button magnets mounted with a spread that mates up with the chosen length stir bar should work fine. A 1" bar is a good length for a 2 liter flasks - it's what I use and it works great. You just need to spend a few moments experimenting with the spread to find the strongest coupling between magnets and bar.

If you want to be able to use multiple size bars, four button magnets may be needed. Hard to say without knowing the parameters (like, what the length range is from shortest to longest). Fortunately magnets are pretty cheap, allowing experimentation.

Or...you can use a pair of bar magnets end to end to cover a range of bars without having to "tune" anything. The ones in this pic are 1" x 1/4" X .1" N42 type with their poles on their broadest surfaces and will work with a wide range of bars. I use a 2" bar on my 5L flask without having to change anything from using the 1" bars. Neither length ever gets thrown even at Tornado Speed

Cheers!

 

[Eugenio]

I originally bought those but didn't work, so I bought this one instead:

http://www.amazon.com/dp/B000UD2UU0/?tag=skimlinks_replacement-20

I wanted to buy em 1/8" th, but only 1/16" would fit in my setup.

I did keep the radioshack smaller magnets tho, glued one to the inside of my cigar box and used it to store the stirbar while not in use (wanted it all together and without trashing on the inside) and glued the second one to a string, which when soaked on starsan is my stir bar retriever. I didn't want to have to fish them out of a carboy a few weeks after.

 

[wolverinebrewer]

Building a stir plate came across rare earth magnet 3/16 size at radio shack are two of these magnets going to do the trick for 2000ml starter? Or of all else could 4 of them side by side work? If that wouldn't work what size of rare earth magnet would work?

I purchased 1/2" magnets from Radio Shack and had to line up 4 to get it to work at all. I couldn't run my plate very fast without throwing the bar. It was a headache so I purchased (2) 3/8"x3/8" round neodymium magnets from K&J Magnetics for about $1.75 each plus shipping. I can run my plate close to 1000 rpm's with no issues. Just don't let them get together or you will have a hard time getting them apart as they each have about 10 lbs. pull force. I have them just under 1/2" apart for a 1" stir bar.

 

[day_trippr]

[...]glued the second one to a string, which when soaked on starsan is my stir bar retriever.[...]

Fishing? I just use a magnet on the outside to drag the stir bar to the top of the flask...

Cheers!

 

[RTL]

The only thing you should be thinking when you look at the size is will it fit in your enclosure and will the poles line up with the stir bars poles. As far as magnetism goes the strength of the magnetic field is measured in units of Gauss. Most magnets however are advertised with their pull force in lbs. I'm not sure if there is a standard for how that is measured but if you're wondering about their ability to hold a stir bar thats what you want to know.