Magnetic Stir Plate




I wanted a stir plate for yeast cultivation for home brewing. I looked on Amazon to buy one but they were $60 + and I really didn’t want to spend that much so I decided to make one myself. All of the parts that I needed other than the cigar box, I already had on hand. This is a bonus because I typically end up spending more money than it would have if I just bought it, so I was excited to make this. Also, second bonus, this was a really quick project. I finished it in an hour. I can’t take credit for the idea - there are a bunch of other people online that have similar DIY Stir Plates but this is my take on it.

Step 1: Misc.

I stopped in the local smoke shop and picked up a cigar box. This was the only thing that I did not have. There were different types and the higher quality boxes were 5-10 dollars each, but this was a cheap one and the guy gave it to me. This worked out perfectly other than it is a little flimsy. If I were to do it again, I probably would have spent a few bucks and got a better box, but either way, this worked out fine.

The other items that I used included a computer fan, an old speed control for a computer fan that I had, a toggle switch, a 12 volt transformer and a rare earth magnet that I took out of an old hard drive.

I placed the magnet on the fan and centered it to the best of my ability. I didn’t glue it down yet because I wanted to be able to adjust it in case it was off center and shakes. It ended up working out fine on the low setting. The high setting vibrated a small amount but I think that was too fast anyway.

I cut a hole in the middle of the box to allow for the magnet to spin freely and I mounted the fan to the box with a few bolts that I ended up counter sinking to make sure that the top would remain flat.

Step 2: Wiring

The wiring is a little hard to see in the picture, but I took the positive wire from the transformer and went into the toggle switch. The other terminal on the switch went to the positive input for the speed controller. Connect the negative from the transformer and the negative for the speed controller together. On the output of the speed controller went to the fan (positive to positive and negative to negative). The blue wire from the fan is not used.

Step 3: Update

So this update is a little later than I thought it would be… My stir bars finally arrived (they were on the slow boat from China). I also ordered a nice big 2L Erlenmeyer Flask, so I thought that would upload a few new pictures. The stir bars were 8 dollars shipped for 7 of them. I really like these because depending on how much agitation (stirring) that you are looking for, you can change the size that you use. I found that the largest stir bar created the most vortex – no surprise. The smaller stir bars are the best for a nice low speed stir for my yeast culture though. I want to keep the culture moving, but it doesn’t need to be really fast. I really like the speed of the small stir bar, but I couldn’t get it to stop clattering aound so I ended up using the larger bar. A little more aggressive than I think is necessary, but MUCH quieter… Reflecting back, I think that if I were to do it again (or maybe I will modify) I would use a variable speed control instead of the three speed switch that I have. That would allow me to have better control over the speed. Either way, I would say that this was a successful project and I am happy I did it!



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    4 Discussions


    Reply 2 years ago

    For the test, I took a small bolt and put some shrink tub around it. This worked for a test run. Looking back, it would have been better to take two bolts and put the head end together and shrink wrap it. That would have created a nice pivot point. The one I made clanked around a little bit. The best thing to use is an actual stir bar. You can get them on Amazon.


    Reply 2 years ago

    PTFE (Teflon) coated magnetic stir bars are the bees knees. They have low friction and don't react with that you're mixing. They add no flavors to the yeast culture and do not affect it. Super awesome for this (or any, really) application.


    Reply 2 years ago

    I agree, that's exactly what I ordered. You can get a pack of different sizes for around $9 shipped. As soon as they arrive, I will update the pictures.