Alternate Stir Plate Design

DrPaulsen · Post by **DrPaulsen** » Wed Oct 20, 2010 8:52 am

A few people have ping'd me with questions about how I built my stir plate, so I took a couple of pictures and posted them to Flickr:

http://www.flickr.com/photos/33275630@N ... 097900761/

As you can see, it's much cruder than the fancy ones built in the last tech meeting (what with their "housings" and "solder"). My design was largely driven by whatever I had lying around. The only piece I had to purchase was the magnets (Magcraft NSN0575/N40 - about $10 at Amazon for more than I needed). I tried using hard drive magnets but could never get them to work with a 50 mm stir bar. They'll probably work with a smaller stir bar, though, if you wanted to try.

One of the differences I've noticed between this design and the one built at the last tech meeting is the magnet attachment mechanism. In mine, a steel backer plate is fixed to the fan (via two-sided 3M foam tape) and the magnets are held to the plate by magnetic force. This provides the opportunity to easily relocate the magnets to ensure they are both displaced equally about the axis of rotation and separated by approximately the length of the stir bar (i.e. so it doesn't wobble and throw the bar). The steel also doubles the strength of the field seen by the stir bar by shorting out the magnetic circuit on one side. The magnets will move a little bit if I turn the fan all the way up without a load on top, but this never seems to happen when I'm actually stirring a flask.

As far as the fan speed control is concerned, I used a universal DC supply. I typically get the stir bar to start moving at around 6V and then run it at 9V.

I'm pretty sure you could do the same thing with an AC fan if you rigged it up with a dimmer switch. I have all the parts to try that but have just never gotten around to it. If anyone wants to give it a try, let me know and I'll get the parts to you. I dug the fan out of the trash and I think I payed $0.10 for the dimmer switch at ReStore (which is a great resource for building brewing control circuits on the cheap).

Lee

brownbeard · Post by **brownbeard** » Wed Oct 20, 2010 9:08 am

I want to find some magnets locally. Shipping on these things is ridiculous.

DrPaulsen · Post by **DrPaulsen** » Wed Oct 20, 2010 9:47 am

You could try calling the IRS (Iowa Radio Supply).

http://www.irsupply.com/

I didn't know about these guys when I bought my magnets, but it seems like the type of thing they would carry or be able to order for you.

BrewHound · Post by **BrewHound** » Wed Oct 20, 2010 1:23 pm

This really is not an alternate stir plate design, the only real difference is the shape of the magnets used and how you very the voltage, you you are varying the voltage using a voltage regulator built into the power supply, we are using one external to the power supply.

I guess another difference is that there is no surface plane covering your magnetic field and we have the lid of the box that covers ours. Both of these are easy to remedy with the units that were built at the tech meeting.

I do appologize for getting the wrong magnets for these. I did not think about the polarity of the fields sitting end to end until after we put these together (Actually my plan was for there to be a 1/2 inch of space between the magnets).

I am more then willing to order a new set of magnets for everyone in bulk. Here are the new ones that I am suggesting:

http://www.magnet4less.com/product_info ... cts_id=830

They are N52 magnets that are 1/2" x 1/2" polarized on the axis (through the flat surfaces).

They would be seperated by 1" of space for a 2" stir bar. However, unfortunately, I can not cover the cost of these myself, I am already in for more then I collected out of the stir plates (by about $30).

The new magnets are 3.40 for 2 of them with about $1 in shipping per person. However, I need to know who would be interested in a new set of magnets? I plan to order a new set for each of my stirplates.

Matt F · Post by **Matt F** » Wed Oct 20, 2010 2:26 pm

Make sure to bring this up at the meeting Thursday. I will be there and can bring some $ for you.

brownbeard · Post by **brownbeard** » Wed Oct 20, 2010 4:13 pm

Harbor freight has them. Going tonight to see what sizes they have.

DrPaulsen · Post by **DrPaulsen** » Thu Oct 21, 2010 8:30 pm

BrewHound wrote:This really is not an alternate stir plate design, the only real difference is the shape of the magnets used and how you very the voltage, you you are varying the voltage using a voltage regulator built into the power supply, we are using one external to the power supply.

By your criteria, wouldn't even professional stir plates fail to qualify as an alternate design? Almost all of them feature a DC motor, magnets, and a voltage regulator circuit. The only exceptions I can find to this are stir plates driven by multi-pole electromagnets where the drive signal frequency would be used to control stir bar rotation speed. Since frequency controllers are pretty expensive and DC motors are dirt cheap, I suspect they are the exception.

With so much similarity between different models, I would argue that all the differences you pointed out should qualify this as an "alternate design" in this field. This is undoubtedly a trivial point, but the inventor in me that spends his time reading and applying for patents couldn't be stopped. Now it's time to drown out that inventor with beer.

Matt F · Post by **Matt F** » Fri Oct 22, 2010 9:35 am

Link to another magent place on the stirplates website. I didn't compare prices, just adding the link. CJ, let me know before you order so I can get you cash as I would like some new magnets.

http://www.forcefieldmagnets.com/catalog/

bf514921 · Post by **bf514921** » Thu Jan 19, 2012 5:35 pm

i just dissasembled an old harddrive i had lying around, pulled the magnet out and sent the harddrive to the recycler. glued the magnet to a fan, took the old computer power supply to hook the fan up to, and mounted it to some wood flush mounted. wasn't pretty but works.

Post by **JimPotts** » Thu Jan 19, 2012 6:28 pm

Believe it or not, we had a (somewhat infamous) tech meeting on that very topic.

Post generated using Mail2Forum (http://www.mail2forum.com)

brownbeard · Post by **brownbeard** » Fri Jan 20, 2012 10:53 am

My advice is to use a small stir bar. With the larger stir bars, my stir plate was little more than a paper weight. Now that I have a small bar, I can run the thing at full speed, and not throw the bar.

Matt F · Post by **Matt F** » Fri Jan 20, 2012 11:02 am

I second the small stir bar experience. I use the same stir plate as brownbeard and the small bar gets a vortex going even when I am doing 4L starters.

bf514921 · Post by **bf514921** » Fri Jan 20, 2012 2:02 pm

when you say small stir bat, is that the One inch stir bar?

hoboscratch · Post by **hoboscratch** » Fri Jan 20, 2012 2:10 pm

I use 25mm and I can get at least a 2l starter spinning.

On Jan 20, 2012, at 2:03 PM, bf514921 <brew-tech@crbeernuts.org (brew-tech@crbeernuts.org)> wrote:

when you say small stir bat, is that the One inch stir bar?

Brandon Franklin

Post generated using Mail2Forum (http://www.mail2forum.com)

bf514921 · Post by **bf514921** » Fri Jan 20, 2012 2:17 pm

yeah thats what i use now, for the 2l, i am thinking i need bigger starters for my lagers.