My homebrew stirplate - Page 33

oregonparamedic · 03-31-2011, 02:53 AM

Just finished up mine. I don't have a stirbar yet but a bent paperclip pulled down a small whirlpool for the test!

nduetime · 11-07-2011, 06:07 AM

A couple of questions...

Would it be better to get a fan with higher RPM's? I understand the lm317 and potentiometer will adjust the speed but I'm thinking of worst case senario here.

Also, does the size of the stir bar depend on all the other factors (placement of fan from flask, magnet quantity and quality, etc.?) I'd prefer not to have to make additional web purchases, paying more for shipping, if at all possible. If there's no way really to predict which bar will be needed for my setup, what are the 2-3 sizes I should get (1", 1.5", 2", etc.?)

Thanks.

CrazedArmadillo · 11-07-2011, 08:13 PM

Quote:

Originally Posted by nduetime

If there's no way really to predict which bar will be needed for my setup, what are the 2-3 sizes I should get (1", 1.5", 2", etc.?)

stir bar size mostly depends on the spacing between the magnets. If your magnets are 1" apart, then a 3" stir bar won't work too well. When I put my stir plate together, I bought the stir bar and some rare earth magnets. Then I stuck a magnet on each end of the stir bar. The magnets will naturally come to rest at the proper spacing. I then glued the magnets in place at this spacing, then stacked an additional magnet on each side for added strength. Works like a champ...never once thrown the bar.

nduetime · 11-07-2011, 11:50 PM

Quote:

Originally Posted by CrazedArmadillo

stir bar size mostly depends on the spacing between the magnets...

Thanks for the reply. Do you have a suggestion on what two size stir bars would be a safe bet?

CrazedArmadillo · 11-08-2011, 05:00 PM

I used a 1.5" bar for my stir plate, and it works great in a 2 Liter flask. The trick to using a larger stir bar is that you can't mount the magnets directly on the fan...they would be too close together. Plus, I'm not a fan of mounting magnets directly on a fan anyway, because they interfere with the magnetic field needed to run the motor.

This is what I did:

I bought these magnets http://www.truevalue.com/product/6-Piece-Neodymium-Super-Magnets/13923.uts at a True Value hardware store. They are very strong, and work a lot better than hard drive magnets.

Then I bought a 3/4" PVC pipe coupling
http://www.homedepot.com/h_d1/N-5yc1v/R-202303522/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

and bought some 1/2" tube straps
http://www.homedepot.com/Plumbing/h_d1/N-5yc1vZbqew/R-100201267/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

The PVC coupling was the same diameter as the center hub on my 80mm fan. I glued it in place, making sure it was balanced. One of the 1/2" straps then fits into the 3/4" coupling, leaving me two perfectly spaced mounting locations for my magnets. I then glued a magnet to each pad, making sure opposite poles are up (and using the stir bar to properly space them). Finally, I stuck an additional magnet on each side for added strength.

The PVC coupling works really well in this application, because it adds space between the fan motor and your magnets....hence, less interference.

In addition, you could assemble multiple 1/2" straps with magnets at different spacing for different sized stir bars....or instead of adhering magnets directly to the straps, place your magnets on a thin, lightweight strip of something that screws on to the bracket. Then, if you need to use a bigger stir bar, you could just swap out the bracket or strip.

EDIT: sorry about the blurry pictures...phone was acting up that day. I also failed to take a picture with the magnets in place...

nduetime · 11-09-2011, 06:49 AM

Quote:

Originally Posted by CrazedArmadillo

I used a 1.5" bar for my stir plate, and it works great in a 2 Liter flask. ...

Thank you for the advise. I'll look at that size when I order.

theveganbrewer · 11-10-2011, 12:47 AM

In case anyone is unfortunate enough not to have a 12, a 9, or even a 6v power adapter in the house, usefulgadget, on ebay is selling the ones needed for this build for 3.89 with free UPS shipping.

nduetime · 11-12-2011, 03:43 AM

Can someone help me out? I'm trying to figure this out but am getting no where. It's my first attempt at soldering and while the information in this post as well as this site are good, my frustration is starting to set in. I'm just looking for help through this.

Here is a quick drawing I did which represents what I have soldered right now.

Does this look right? Also, where does the on/off switch get wired in at?

If anyone is kind enough to help, I would greatly appreciate it.

Thank you, in advance.

nduetime · 12-20-2011, 12:00 AM

ok....so I now have the fan running. I have two problems.

The first is it doesn't seem to have any adjustment in the fan/POT. It's only a 500 RPM fan (super quiet) so I'm not sure if that really has anything to do with it.

Second, I don't have the on/off switch wired in because I'm a little confused how to do so. Can anyone post a picture of where it is in line with the other devices? I just need a photo to reference.