My homebrew stirplate

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

P1030383.jpg
 
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.
 
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.
 
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...

IMAG0763.jpg


IMAG0764.jpg
 
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.
 
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.
lm317001.jpg

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.
 
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.
 
Hello all,

I built my stir plate out of magnets from Home Depot and have a 12v 2 amp DC computer fan turning it. The problem is though every time I place the stir bar or anything mettle on it is throws it off? The stir bar is a square type like these. What I was wondering is why does it seem to be doing this?

Thanks
cd
 
I'm happy to have found this thread but it's been running so long maybe it's too late to join in.

I've been making yeast starters for a while but not really doing it right. I haven't stirred mine at all because John Palmer's "How to Brew" doesn't mention it. I also use a regular S bubbler airlock but that doesn't let oxygen in. I just let my Trader Joe's apple juice bottle sit for 24 hrs - who needs to spend money on a flask? (that's rhetorical folks!)

So I'm going to build a stir plate because I'm better at building things than I am at parting with money. As I read through this thread a couple of things come up that I'm not so clear on. I see the need for speed control but not sure why anybody (particularly the inexperienced) would opt to build a control circuit with several components if an appropriately rated rhesotat/potentiometer would do the trick.

I'm planning on using a spare 12v 1000mA adaptor from a damaged ext hard drive (which I threw away long before I got in to yeast starters otherwise I'd also have magnets:() I saw this on eBay http://www.ebay.com/itm/251224703150?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648 and I'm going to see if my local Fry's has one when I'm in there looking for the fan, case, hardware etc. Or I'll just get that one on eBay.

Since I don't have access to a hard drive I'm going to get these magnets: http://www.harborfreight.com/10-piece-rare-earth-magnets-67488.html which brings me to the next point. The hub of the fan will spin in a circular fashion. Why are some people putting two or more magnets spaced apart? The resultant magnetic field pattern is going to be circular and rotating however the magnet(s) are laid out - isn't it? For that matter one could get a circular magnet: http://www.harborfreight.com/40mm-round-magnet-96649.html

On the same topic, where people have used more than one magnet why are they installed with opposite poles up? But like I say experimentation will probably be the key.

Anyway, thanks for the great and inspiring thread. If anybody can shed a little light on the above I'll appreciate.
 
Sorry I don't always catch when this thread pops back up.

As to why go with a circuit vs. a rheostat or a pot I covered that in this post. Rheostats or pots will work but I think this is a better option and at the time I had the parts to make one already.

https://www.homebrewtalk.com/f11/my-homebrew-stirplate-8850/index3.html#post88059

As for the magnets, I used 2 magnets because a larger magnetic field seems to keep the stir bar more stable. You may be able to go with 1 centered magnet but if its off center any the stir bar will go off kilter and get thrown. This can happen even with 2 magnets if the speed is too high. As you will see if you ever try to build one of these the magnets need to have the poles opposite on the 2 magnets or the stir bar will not center. It will be obvious when you try it what happens. The more powerful magnets the better for keeping the stir bar centered. You will see that you may be able to keep it going just fine in water but as soon as you add a more viscous liquid (your starter) you may find the bar tends to get thrown more. Hope that helped.
 
I see the link recommends a 10K OHM 1/4 Watt Pentiometer/Rheostat. I used - I think - a 100K OHM 1/2 Watt rheostat from radio shack (says "A100K"). It throws the 11/2" stir bar really easy, could this be the cause? The closest thing I can get is a 10K 1/2 watt, - would that work? I also have a 1" stir bar with ring and one w/out ring in the mail to try, and I'm going to try 2 hard drive magnets instead of one in the center...
 
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