Stir Plate question

[cfrazier77]

I just built two plates using HD magnets and 2 in bars. They worked good with water. Wort is a different animal.
I had a starter going for two days, and my wife called me at work today to tell me "your beer thing is making a loud funny noise".
Please turn it off honey... "I already did, how much longer does this have to be in the kitchen???"
I'll move it today honey.

Luckily the starter is done, but it threw the bar on the lowest speed.

I may end up buying one.

I have only made one starter, and this happened with my stir plate that I made with HD magnets. However, I put two carpenter pencils on top to raise the flask and everything worked fine. I did order some of the above recommended magnets and will use those for my next starter.

 

[camiller]

I just built two plates using HD magnets and 2 in bars. They worked good with water. Wort is a different animal.
I had a starter going for two days, and my wife called me at work today to tell me "your beer thing is making a loud funny noise".
Please turn it off honey... "I already did, how much longer does this have to be in the kitchen???"
I'll move it today honey.

Luckily the starter is done, but it threw the bar on the lowest speed.

I may end up buying one.

I have only made one starter, and this happened with my stir plate that I made with HD magnets. However, I put two carpenter pencils on top to raise the flask and everything worked fine. I did order some of the above recommended magnets and will use those for my next starter.

The only time I had this problem was due to the HD magnet shifting (At first I thought it would be strong enough to hold itself to the washer without glue. Once I re-centered and glued it I never had this problem again.

 

[mccumath]

I bought the magnets from harbor freight, and had to make larger spacers to move the fan as close to the top of the stir plate as the bolts would let me, then hot glued 3 magnets on top of each other to make the rest of the gap. Works great with water on the lowest setting, but I am yet to try with wort. Will see how it goes.

 

[thargrav]

There are so many people using hard drive mags I am wondering how they are getting them to work? I am waiting for my parts to arrive and I will be putting mine together.

I finally took apart a failed hard drive and did some testing and at least with the one I took apart, can tell you why the hard drive magnet won't work well.

The hard drive magnets (there were two in the drive, opposite each other) were not rectangular magnets, they were made into a arc. The magnets seemed strong enough but because of the way they are made you can't center the N and S poles directly across from each other without throwing everything off balance. When mounted with the N and S poles directly across from each other, most of the magnet weight was to one side of center and this caused a serious vibration problem kind of like your cell phone buzzer but 10 times worse.

Then when I mounted the magnet so the weight was balanced the N and S poles wanted to pull the stir bar off center towards the N and S poles. The stir bar wasn't pulled far off center but it was enough to cause the stirbar to throw at any speed but the lowest setting.

Either of these issues will cause your stir plate to throw the stir bar. You stir bar has to spin centered above the motor with as little as possible to pull it off center.

It seems that hard drive magnets would work great if they were made into a straight bar. Has anyone taken a hard drive apart with magnets made this way? If so you should share the make & model number with the list.

 

[kh54s10]

I made mine with hard drive magnets and old power converters from ?? I glued the magnet on the fan and it quickly came loose from the glue. I now have it holding to the fan by its own magnetism.

The first power converter spun the fan too fast and would throw the stir-bar. I then used one from an old answering machine and it works like a charm. I am using a 1" stir-bar. I put a rubber o-ring in the center to make it spin better.

 

[camiller]

I finally took apart a failed hard drive and did some testing and at least with the one I took apart, can tell you why the hard drive magnet won't work well.

The hard drive magnets (there were two in the drive, opposite each other) were not rectangular magnets, they were made into a arc. The magnets seemed strong enough but because of the way they are made you can't center the N and S poles directly across from each other without throwing everything off balance. When mounted with the N and S poles directly across from each other, most of the magnet weight was to one side of center and this caused a serious vibration problem kind of like your cell phone buzzer but 10 times worse.

Then when I mounted the magnet so the weight was balanced the N and S poles wanted to pull the stir bar off center towards the N and S poles. The stir bar wasn't pulled far off center but it was enough to cause the stirbar to throw at any speed but the lowest setting.

Either of these issues will cause your stir plate to throw the stir bar. You stir bar has to spin centered above the motor with as little as possible to pull it off center.

It seems that hard drive magnets would work great if they were made into a straight bar. Has anyone taken a hard drive apart with magnets made this way? If so you should share the make & model number with the list.

I made mine with a single hard drive magnet and it works well at any speed except the very highest (any voltage from 3v-9v is OK, 12v was to fast, 1.5v and the fan stalls. My power supply is variable from 1.5v to 12v in 1.5v steps except there is no 10.5v). As you said, you have to align the magnetic field across the diameter of the fan and not the weight. With mine there is no significant vibration, although I did use a fender washer on the fan which gives the fan more rotating mass than without it so the amount of imbalance due to the uneven distribution of the magnet's weight is comparatively small. For my magnet the center of mass and the magnetic center are within perhaps 1/16" inch anyway, so there was not a huge imbalance to start with.