Stir bar woes, aka, is this normal?

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mezman

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So I'm going though the home stir plate assembly that everyone seems to do. I took the magnets out of an old hard drive and got two strong magnets. I have a 120mm fan that I mounted them on (stuck together). But the stir bar always gets thrown. I think I centered the magnets well, the fan doesn't vibrate wildly or anything.

I think that the problem stems from the magnets grabbing the stir bar at one end only and swing it around the bottom of the flask like a wrestler with a guy in a helicopter move. I figured that the north and south poles of the magnets on the fan would grab the south and north poles of the stir bar and center the stir bar over the magnet. That's not happening in my case.

So my question to you with stir plates, does the stir bar center itself over the magnet or align itself off center?

If your stir bars self align, do you think my problem is my stir bar or the magnets?

:confused:
 
Sometimes you have to play around with them a bit. You can adjust the distance from the magnet to the bottom of the flask by adding height to the top of the fan with pvc tube and things like that. Also for mine, I place the flask on the box with the fan off and get the magent lined up with the stir bar in the center of the flask, then turn the fan on at low to medium speed.
 
if the magnet halves are too close togeather then the magnetic field will cause the bar to throw. ALso if there isnt enough vertical distance the fields will overlap too much and cause the bar to not spin properly. In this case i would guess you need more vertical clearance....try holding the flask slightly above and see if that solves your problem. If it does then just use spacers to replicate it
 
I have seen workable designs that use just one HDD magnet. I suggest you give that a try because with one magnet you won't have the spacing and pole interference issues that develop using two magnets. The HDD magnets I see are certainly large enough to spin a stir bar.

Keep us posted on how it goes.
 
Try putting the stir bar right on the magnets, with no flask. If one of the magnets is backwards, it won't sit on both of them, or spin right.
 
Additionally, I have one flat stir bar and another with a ring on it. The flat one gets thrown more often due to the increased friction.
 
Wow, that's a lot of overnight replies! Thanks for the quick turn around. :)

I'll have to play with it more when I get home from work and try increasing the spacing, but if I put the bar right down on the magnet, it slides off to one end of the magnet and can't be centered at all so I'm dubious about how much help adding space between the magnet and the stir bar will help.

With respect to these shots, if you allowed your stir bar to stick to your HDD magnet, how would it line up?

Like this?
704107662_rMXNc-X3.jpg


Or like this?
704107660_ibDzX-X3.jpg


My stir bar is lining up like the former which is what's causing the instability in the spin and causing the bar to get thrown even at hand spun speeds.

Also, sorry about the craptastic power point drawings, but I'm at work and that's all I have right now.
 
It should line up in the center of the magnets like the last picture. You might have to flip one of your magnets to get the poles correct.

Or...The center axis of the stirbar should align with the center axis of the spining fan.
 
OK, I got the magnet to hold the stir bar in the middle, now I need to get it balanced so it stops throwing the bar at speeds high enough to get the dimple lower than half an inch from the surface in my 2L flask.

So, tips and tricks for balancing the magnet?
 
If you accelerate the RPMs of the fan slowly, you shouldn't throw the magnet. If that doesn't work you may need to stack more magnets inorder to get it up to speed.
 
Your almost there.....

I used 1 HDD magnet, I was unsuccessful with 2 HDD magnets as all 6 I pulled seemed to have a different magnetic pull among them.

Try and line the the magnet and stir bar up, like your lower drawing.

Once you have that done, I've found in helping a few other locals that the next item is the distance from the magnet and stir bar. Too close you may not spin up or the magnets drag on the box... too far and you will toss the bar.

If your bar is solid to your HDD magnets like the lower pic and your still throwing the bar, I'm most inclined to suggest adjusting the distance between the HDD magnet and the stir bar.
 
What size bar are you using? I started off with a 3" bar and couldn't get it to hold. Switched to a 1" bar and it works like a champ. I use a 2000ml flask and get enough of a dimple to facilitate good O2 exchange.
 
I'm using a 2" bar that I bought off ebay. I think at first my bar was all funkily magnetized. But after spending a night attached to the HDD magnets, it snaps right to the center now.

Unfortunately I snapped one of the magnets last night while I was trying to get it centered. So now I'm down to one magnet only.

I'm trying to get my magnet properly centered on the fan hub to get a balanced spin. Where I've had it going, the stir bar isn't neatly spinning around it's own center point but slightly off and I think that's what's causing it to get thrown at higher speeds.

I'm getting closer to getting this thing to work for me. I think if I can get the HDD magnet nice and centered around the fan's axis, I might be golden. It's surprisingly hard though (for me at least) since the HDD magnet isn't a nice simple rectangle shape.
 
I have built two stirplates with nothing but scrap stuff and hot glue. I highly recommend the hot glue gun for temporarily tacking down the magnet. Hot glue is easy to cut away with an exacto, but holds extremely well. I'll try to post a pic when I get home.

Also, I have to again mention that I have had (by far) the best success with a 1/2" bar. I do have longer bars, but this works the best. Don't worry about the vortex, the 1/2" sucks a tornado through a 4L no prob. Maybe I'll get you a pic of that, too.


OK, found a pic of the one I made for my friend (his pic in his 2L flask). Again, this is a 1/2" bar.
P1010862.JPG
 
Glue gun is a good idea. I epoxied a large washer to the center of the cpu fan, then just put the magnet on the washer. This allows you to adjust the magnet until you get it where you need it.
 
I recently made a home made stir plate too.

What helped for me was to use double-sided sticky tape to temporarily hold things in place while I figured out the magic combination:
- wood disk on top of the fan (keeps the fan from locking up from HD magnet's pull)
- large metal washer
- two hard drive magnets (my HD came with two small curved magnets)
- 1.5" stir bar

I wound up with about a 3/4" gap between the HD magnets and the stir bar.

I will post pictures of the set up to Anthony Lopez's thread soon.
 
Also, keep in mind some vessals have a domed or uneven bottom that will throw stirbars....its frustrating both in a laboratory as well as homebrewing. Hope this helps.
 
In many cases the longer the bar the more easily it gets thrown due to the greater resistance of the bar. 1 to 1-1/4" is plenty in most applications. The thickness of the bar does as much or more to created good mixing then the length.

You really don't need the vortex to extend all the way down to the bottom. If you have a dimple and can see the wort rotating then you are good. Just keeping the yeast in suspension and driving off the co2 to facilitate some gas exchange is all you need.

As to the magnet you broke, it can still be used as long as both pieces are about the same size. Take the two ends and physically stick them to the stir bar, one near each end of the bar so you know the pols are lined up correctly. Now set your stir bar magnet side down on the fan where you want to mount it and mark where the two halves of the magnet are sitting on the fan. Now you know where to mount the two halves so they line up correctly with the poles of the stir bar.
 
I have a working stir plate now! And I can use it to start my first starter tomorrow for a brew-day next Wednesday.

705311849_trgVR-X3.jpg


705311868_gVFFa-X3.jpg


That's about as far as I can get the vortex down my 2L flask without the bar getting thrown but, from what I understand, that's more than enough. I'll crank it back tomorrow for an actual starter, I don't want the bar getting thrown when I'm not around watching it. Plus it rattles a little, I don't think I have the washer I stuck the magnet to perfectly centered on the fan hub, though it's pretty close. I think that's why I can't really crank on it and up the voltage above about 5.5V with any hope of keeping the stir bar in the center. The stir bar is spinning around an axis that's not directly in the center of the bar so it doesn't take much speed with a 2" bar to get that mass moving off in one direction instead of staying confined to the center of the flask so it's probably like Zen Brew said. I think I'll invest in a 1" bar to give me more confidence in it staying spinning while not supervised. I wonder if the decreased masses of those smaller bars would help them stay where I want them.

But anyway, thanks for all the help and suggestions! Now I gotta use this new found power for more than watching grape parts get swished around a flask! :fro:

EDIT: Forgot the obligatory homebrew in the shot. That's been corrected now. :mug:

705332545_Jn6Ue-X3.jpg
 
Just an update and thanks to all:

I picked up 1" and 1/2" bars and they stay centered a lot better than the 2", so I have that going for me now. It rattles a lot though. It's not a problem because I have the plate set up in the guest bath and we don't usually entertain guests, so no one's around anyway.

My most recent beer was pitched with a starter made on the stir plate and I've not seen such a vigorous ferment in a while, so it looks like it's working as intended.

Thanks again to all!
 
Just an update and thanks to all:

I picked up 1" and 1/2" bars and they stay centered a lot better than the 2", so I have that going for me now. It rattles a lot though. It's not a problem because I have the plate set up in the guest bath and we don't usually entertain guests, so no one's around anyway.

My most recent beer was pitched with a starter made on the stir plate and I've not seen such a vigorous ferment in a while, so it looks like it's working as intended.

Thanks again to all!

mine rattles a bit at high but if I play with it and get centered it stops also the chatter comes when the vortex hits the stir bar



this was with 12 volts I went to 9 volts and it super quiet. 1/2 stir bar like passdown
 
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I was under the impression that you don't actually want to create that big of a vortex, more like a small dimple in the wort? Why such a big vortex?
 
Stirring keeps the yeast in suspension, instead of caking up at the bottom. Suspended, they'll keep in contact with the DME and eat and thrive. A vortex is not necessary, but it won't hurt, as it may pump in a bit more oxygen. The yeasties like that!

Say - I wonder if you could avoid a vortex, but stir an actively fermenting 5 gallon wort....

bet those would be some low FGs
 
I use a 2" bar and I had a really difficult time getting it centered so it wouldn't get thrown. I started with HD magnets, but finally settled on some neodymium (sp?) magnets from Michael's. I found that my stir bar has the same polarity at both ends (which surprised me). I also added a second potentiometer so that I have two in series. This lets me run much slower which seems to work great. (Actually, I have a starter cooling in the sink right behind me. It goes on the stir plate in a few minutes!)

Also, nice use of a pleasant flower arrangement as a backdrop for your pictures. I think we should start expecting everyone to include some nice props in their pics!
 
I was under the impression that you don't actually want to create that big of a vortex, more like a small dimple in the wort? Why such a big vortex?

Wort and water act differently the wort is more viscous and creates less of a vortex at the same speed setting

I usually leave the stir plate on low at first and then I turn it up a little as the yeast grow because the starter gets more viscous as they grow . The vortex wont hurt the yeast at all anyway
 
I'm using a 1" or 1 1/2" star shaped bar and man does it make a vortex. On high its slurping like someone at the bottom of a milkshake. I used a single hard drive magnet spaced off the fan w/ acrylic, I noticed if I didn't it caused a lot of drag on the fan. Who knows if I need that kind of vortex but its cool to watch.
 
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