DIY Stir Plate Problems

[WrongCoastBrewery]

So I decided to DIY on a stir plate. Got a 120mm fan, rheostat, switch, 12 vdc power supply, HD magnets, and a stir bar from Brewmasters Warehouse. Put it all together and the stir bar wont spin when the plate is on. I used two HD magnets on either side of the fan hub and just a single one in the middle. I even used two stacked on each other. The fan spins just fine, responds to the rheostat, but no matter what the stir bar wont spin. It does spin just fine directly on the magnets. Too much space between the magnet and stir bar? Thoughts?

 

[FireBrew63]

Too much space is my first thought. I had to fiddle around with the spacing on my DIY until I got it to the sweet spot. Works like a champ now and cost <$6 to build!

 

[WrongCoastBrewery]

Too much space is my first thought. I had to fiddle around with the spacing on my DIY until I got it to the sweet spot. Works like a champ now and cost <$6 to build!

How did you adjust it or fiddle with it?

Could it be the fan itself?

 

[FireBrew63]

I glued hard drive magnet onto the fan, then added spacers to the top outside corners of the fan shroud until the stir bar spun with no problems.

 

[WrongCoastBrewery]

I did that and used only one copper washer on each corner. The stir bar spins just fine on the top of the stir plate. But it still wont spin in the flask. I am using a cheap small plastic tote for my enclosure.

 

[WrongCoastBrewery]

Well, I do believe this one may have kicked my ass. I can get the dang fan to spin at various speeds, turn off with a switch, I can even get the stir bar to spin directly on the magnet just fine. I cant however get it to spin in the flask. Any help would be appreciated. Could my magnets be not powerful enough?

Otherwise I will be buying a stir plate.....

 

[devildancer]

It's not throwing the magnet is it? I built one and only used one magnet on one fan blade, worked pretty well. You are setting it up with the stir plate off, then starting it very slowly, right?

 

[WrongCoastBrewery]

It's not throwing the magnet is it? I built one and only used one magnet on one fan blade, worked pretty well. You are setting it up with the stir plate off, then starting it very slowly, right?

Yeah, it is throwing the stir bar. Yeah, I start it at slow and then slowly bring it up. I am starting to think its the bar actually. I got a 2" bar and it seems to like to only stick to half of the magnet. I think I have the spacing down. Now it seems that the bar just doesnt want to stay with the magnet. I might try to find a 1" and see what happens.

 

[devildancer]

One thing that helped me was to put some pressure on the flask, pushing it down into the stirplate until it started to spin. I don't know why, but it worked. My flask overflowed and killed the one I made. We went ahead and purchased one, a real nice one, and it is awesome. Just throw the flask on and crank the knob.

Edit: It takes more force to start the stir bar in motion than to keep it in motion. I guess the speed required to start it is too much for sustained operation. I do remember having to turn the knob until I heard it spin, then quickly turn it back down. Hope this helps!

 

[FireBrew63]

Aww yes, the 2" stir bar might be it. I have several and none work for me, I use the 1". Another thing might be a concave bottomed vessel. My Erlinmyer flask is slightly concave. That can cause the bar to fly off.

 

[Waunabeer]

I just built one last weekend and had the same problem. Stir bar in the flask would start to spin and then fly off. Had two magnets on at first; then went to one centered. Worked better, but still flew off after a couple of seconds. If I put the flask directly onto the fan (without the lid closed) it works perfectly. I guess the problem is there is too much gap or the wood is just too thick for proper attraction.

Try it directly on the fan and see what happens. Sit the flask with bar on the fan (you will see the bar line up with the magnet), then start up the fan. Works perfectly now.

 

[jroot]

I fabricated my stir plate from a 12V computer fan and HD magnets also and use my hobby variable power supply. Purchased a 1" stir bar but could never get it to spin at all so I cut a 1-1/4" length from some SSteel 1/4" rod I had and placed it inside a 1/4" ID vinyl tube of the same length. This homemade stir bar has no problem in spinning the water in either my 1000ml or 2000ml flask. Seems like the problem as far as I can tell is the length of the rod used. It has to be close to the same length as the distance between the two magnetic poles of the HD magnet used. Sanitize the vinyl tubing and SSteel rod between uses.

 

[bja]

I cut a 1-1/4" length from some SSteel 1/4" rod I had and placed it inside a 1/4" ID vinyl tube of the same length. This homemade stir bar has no problem in spinning the water in either my 1000ml or 2000ml flask. Seems like the problem as far as I can tell is the length of the rod used. It has to be close to the same length as the distance between the two magnetic poles of the HD magnet used. Sanitize the vinyl tubing and SSteel rod between uses.

Are you sure that rod is stainless steel? If it is, it shouldn't work.

Some grades of stainless are slightly magnetic and may work, but they will also rust.

 

[WrongCoastBrewery]

Yeah, I finally got it to work last night after using small copper washers to shim the flask. I downgraded to a 80mm fan and had to rewire everything. Even still the stir bar still get thrown at full speed. At all other speeds up to about 75% on the rheostat, its noisy and barely hangs on. Still gets thrown every now and then. Looks like I need a smaller stir bar.

 

[bja]

Get a 1" bar. Mine works great.

 

[sauerj67]

I just got down making a diy stir plate and I was running into the same problems. I was about to through the whole project into the trash, until I read this thread. I just fixed it!!! finally!!! What was happening was the stir bar, which is 1.5", would not spin like it was supposed to and it would fly off. It was not spinning like a top, it was "chasing the mouse" around in a circle. So, I have (1) 3/8x7/8x1-7/8 ceramic magnet that I placed directly on the middle of the fan, I then took 1 neodymium magnet that I placed in the center of the ceramic magnet. It does not have a problem spinning true now. Try it out, it worked for me.

 

[Catt22]

A DIY stir plate with properly positioned, aligned and balanced magnets should be able to easily handle a 2" stir bar without problems and it should also run quietly without a lot of vibration. It should also be capable of self starting in the event that power is interrupted for whatever reason. I would settle for nothing less.

 

[Ichthy]

Yeah, it is throwing the stir bar. Yeah, I start it at slow and then slowly bring it up. I am starting to think its the bar actually. I got a 2" bar and it seems to like to only stick to half of the magnet. I think I have the spacing down. Now it seems that the bar just doesnt want to stay with the magnet. I might try to find a 1" and see what happens.

My stirplate was always throwing stir bars. The problem was too much power. I had to use a 5V power supply.

 

[WrongCoastBrewery]

My stirplate was always throwing stir bars. The problem was too much power. I had to use a 5V power supply.

My power supply is adjustable from 3V to 12VDC. It never throws unless at full 12VDC. I always see the stir bar not centered so I am to the conclusion the stir bar is the last piece of the puzzle to fix.

 

[Ichthy]

For what it's worth, you only need to run the stir plate fast enough to create a dimple in the top of the starter. There is no benefit, and possibly some harm, to pulling a vortex all the way to the bottom of the vessel. If you don't have any problems with throwing the bar at low speed and it will dimple the starter, I would leave it be.

Good luck!

 

[WrongCoastBrewery]

For what it's worth, you only need to run the stir plate fast enough to create a dimple in the top of the starter. There is no benefit, and possibly some harm, to pulling a vortex all the way to the bottom of the vessel. If you don't have any problems with throwing the bar at low speed and it will dimple the starter, I would leave it be.

Good luck!

Oh, thats what it is doing for sure. But even at low speeds, the length of the bar causes it to be off centered and then it throws. I wouldnt trust it to leave it unattended for now.

 

[vtec4me21]

I would take pictures but my enclosure is siliconed shut for waterproofing. Looks like this one though: http://www.stirstarters.com/images/assy.JPG A few things that worked for my stir plate build was a 1" stir bar. It centers perfectly with the magnet poles. A larger stir bar may be getting thrown as it's not over the magnet poles. 80mm fan with a spacer built from 1" pvc, and I used Gorilla glue. I notched the top of this spacer so the magnets would fit flush to the top of the spacer and glued two magnets one in each notch in the spacer. If you have your stir bar handy make sure the magnet centers to the edge of the stir bar. I cut the spacer so it would just clear the top of the enclosure leaving maybe a 1/4" space. The spacer gets the magnets closer to the stir bar in the flask and keeps the magnets away from the fan which can cause resistance while spinning. Another issue I ran into is magnet polarity. At first I had N up on one and S on the other, didn't work. Flipped one magnet and works great now. I got the magnets from Hobby Lobby. They are not rare earth, come in a three pack and are strong enough to pinch fingers

Are you using just a rheostat in the circuit? I would suggest using a circuit as described here:
https://www.homebrewtalk.com/f11/my-homebrew-stirplate-8850/
https://www.homebrewtalk.com/f11/my-homebrew-stirplate-8850/index3.html
I used this one minus the blue led. The LM317 voltage regulator used with the rheostat really helps fine tune the voltage so you get consistent rotation from the fan and reduce chances of throwing the stir bar. All these parts can be bought at Radio Shack including the heat sink for the voltage regulator.