8 replies to this topic

[Darin]

OK, so I'm making sure the stir plate is working by doing a dry run......... filled up the 2000ML flask with water and tossed a stir bar in. Made sure the stir bar was lined up with the magnets and turned on the stir plate. I had the fan spinning on the lowest setting...... the stir bar was spinning just fine and then it threw the bar. Everytime I tried to get it to go, it would spin for a couple seconds and then throw the bar. Any ideas as to what would cause this?It's a homemade stir plate. I used a "project box" from radio shack....... a computer fan............ two rare earth magnets attached to the top of the fan assembly (each magnet is about a quarter inch in diameter). It has worked before many times and now all of a sudden it's throwing the bar. I don't get it.Please help.Darin

[ncbeerbrewer]

I am figuring that you have your magnets at like 12 and 6 or across from each other on the fan center? You had success with the current configuration of your Rare Earth Magnets and your current stir bar? My thought is that you are not using an undersized magnet. Is the bottom of the flask flat or curved? If its curved that will cause a problem and allow the stir bar to slide side to side. I would think either the flask or possible the stir bar might need to be replaced. I had to try a couple of stir bars before I got mine to work well too.

[MyaCullen]

try adding a spacer between the plate and flask, I did this with mine on a whim and it ran for a week without throwing the barI used a CD case

[djinkc]

I really don't remember what the problem was but I had to work on mine and it started throwing the stirbar when I was done. Since I save every wall wort that we ever had, I swapped out to a lower voltage one. Fixed.

[Tankard]

I have the same problem. My homemade stir plate will throw the bar whenever there is more than 1000 ml of water. The magnets have to be very well balanced to be able to stay connected to the stir bar while moving that much liquid. I ended up buying a stir plate from stirstarters.com (only $42... not bad) and it has a much better design. I can make 2 liter starters easily now.

Edited by Tankard, 18 July 2010 - 04:32 PM.

[MtnBrewer]

Have you guys tried using the stir bars with the ridge down the equator? Seems like that should help keep the bar in sync with the magnets.

[MyaCullen]

Have you guys tried using the stir bars with the ridge down the equator? Seems like that should help keep the bar in sync with the magnets.

I have the 1.5 inch ones octagon cross section with a divider like this

[zymot]

What type of fan are you using? (i.e. 12 VDC, 120 VAC, etc) What are you using to vary the input to the fan?I suggest some testing is in order. Take some variables out of the equation.Set the flask aside. See if you can get the bar to spin while sitting on top of the plate. see if you can control it from zero RPM to throws the bar. The stir plate I made I had plenty of room on the top end. In other words, it always threw the bar with plenty of room to go in the "turn up" direction.Question. Can your speed control go from zero RPM to max?This will probably give you some scuff marks on top of the plate to let you mark the center point of where the stir bar likes to spin. This is where the center of the flask wants to be. Depending on the shape of the magnets you used, the magnetic center could different than the geometric center .If you can spin it on the plate, next add the flask but no liquid. Can you get a good zero RPM to throws the bar?If so, next step add water. Can you go from zero RMP to throws bar with a gradual steps up?Lastly, do a spin test with wort. I was surprised by how much 1.050 OG wort loaded down my stir plate. FWIW This is with a 12 VDC muffin fan and a 0-12 VDC power supply.As far as stir bars are concerned, my empirical observation says that short and fatter stir bars work better than long and skinny stir bars.Let us knwo what you learn. I might be able to provide soem additional help in the way of a reliable speed control.zymot

[Darin]

I attached new rare earth magnets by first attaching them to the stir bar then gluing them as centered as I could on the fan assembly. After reattaching everything, I put some water and a stir bar in the flask and hit the on button..... it works again!!!Thanks for everyone's advice and tips. It really helped!Cheers,Darin