Stir plate throws the bars

[fretman124]

I can't get my stir plate to work, always throws the bars.

I have two rare earth magnets, polarity opposite mounted to the fan. I have three sizes of bars, from 1/2 inch to 1 1/4 inch. I use a oring on the bars to help with spinning.

I have a 2 liter flask and am planning on making a 2 liter starter. I brew ten gallons so will divide between two fermenters.

I can make the bars spin slow. so slow the flask barely has a dent in the surface of the liquid. The middle size bar works the best, the smallest and largest don't work at all.

If I put any of the bars on the stirplate without the flask, they will spin at full speed with no problem.

I saw a thread about starbust stirbars, but didn't see a link.

Any help?

 

[ajf]

I have a stir bar with a pivot ring which always makes a terrible noise, and often gets thrown when stirring at a reasonable speed. I also have some larger bars without the pivot ring. They tend to be a little more difficult to start (I need to start very slow, and spend 5 - 10 minutes increasing the speed), but they don't rattle, and they never get thrown.

-a.

 

[the_bird]

Yeah, I'm having a ***** of a time getting mine to work. Not knowing better, I bought a 2" stir bar, which seems to be too long. Love to find a starburst one if I need to buy another, seems like it's a better design.

Here's a link (never ordered from them, though).

http://www.coleparmer.com/catalog/product_index.asp?cls=5658

 

[Funkenjaeger]

Are you sure your magnets are placed accurately? If the bar is not properly centered with respect to the axis of rotation, it's going to get thrown much more easily when you speed things up.

 

[raceskier]

Is it a homemade stirplate? You may need more magnet. (More Cowbell!)

 

[the_bird]

I'm going to try doubling (or tripling) the magnets up tonight. Got a bunch of recangular ones I can stack on each other. Still seems that my stir bar is too large.

What's the spacing between the magnets supposed to be like? Half an inch or so?

 

[GilaMinumBeer]

I had the same problem with mine til' I glued a dip tube o-ring on to make a pivot point. Woks like a charm now.

 

[fretman124]

Are you sure your magnets are placed accurately? If the bar is not properly centered with respect to the axis of rotation, it's going to get thrown much more easily when you speed things up.

The stir bar seems to "auto center" when I drop it in. Alot of time was spent making sure the flask is centered to the fan magnet

Is it a homemade stirplate? You may need more magnet. (More Cowbell!)

I have to 1/2 inch (about) rare earth magnets spaced about 1/2 inch apart. On top of those I have a hard drive magnet which is the strongest little magnet I have ever seen. I haven't tried it, but I think this thing would spin a 6" cresent wrench

 

[Funkenjaeger]

The stir bar seems to "auto center" when I drop it in. Alot of time was spent making sure the flask is centered to the fan magnet

Well yes, the stir bar will stick to whatever position the magnets are in when you drop it in. The centering of the flask shouldn't matter THAT much, I hardly put any effort into centering mine and it rarely throws the bar. The important thing is whether the magnets are placed such that the stir bar rotates about its center point, rather than being off to one side. It should be quite easy to see if you just stick the stir bar on there with no flask and spin it up. If your stir bar has a ring around the center for it to rotate on, it should be even easier to see - if it's centered properly there should be a point that looks stationary in the center on top of the bar when it's spinning.

 

[RobertHSmith]

Your magnetic field probably isn't large enough, strong enough doesn't sound like your issue (sorry if that sounds like some sort of viagra ad).

I used ceramic magnets from Lowes with my DIY stirplates, pics on my website in the middle of this photo gallery: 08-31-2008 -- Various Pictures

I put the two magnets in line with each other, longways, stuck together. I taped them together and then to the top of the fan. Nothing fancy just plain bare-bones DIY.

 

[homebrewer_99]

Here's a brain teaser for you:

I made my own stir plate using the directions on this site.

It worked fine for a year then it started throwing the stirbar also.

Removed the cover, checked magnets...magnets still in place. Thought center ring on stirbar looked worn so I replaced stirbar.

Stirbar still gets thrown...used another flask...same problem.

Placed water in flask...stirbar works like a charm (like it's supposed to).

Replaced water with wort...gets thrown in .5 seconds time.

Any guesses because I'm stumped???

 

[RobertHSmith]

I have to start mine by running it at full speed and then unplugging it. I quickly set the flask on the plate and wait for the stirbar to center and stop banging around. I immediately plug it back in and then quickly turn down the speed. Not sure how you are starting yours, but a differnent starting technique might be a cheap solution.

 

[eddie]

Try stacking your magnets in the center of the fan. This is what I've done and it works like a charm for the three stir plates I've made.

 

[homebrewer_99]

I don't think magnet strength is an issue here since I can place several books (including a phone book) between the plate and flask and get the same results...but I'll give it a try this weekend. Thanks.

 

[fratermus]

I'd play with different stirbar sizes. I got an assortment of 5 (from 2" to something like 3/8") and different viscosities and flask sizes seem to like different stirbars. Got a 5pack off eBay. I use the tiny one in my 50ml flask and the 1" in 1L flask most often.

 

[BarleyWater]

I don't think magnet strength is an issue here since I can place several books (including a phone book) between the plate and flask and get the same results...but I'll give it a try this weekend. Thanks.

After magnets have been near each other for a long time, their polarity can shift . If you have two magnets, and you force them together, and hold them there for a LONG time, they will eventually stop resisting each other as much, and the polarity swings around to be where it wants to be, so they will no longer repel each other on that side. Maybe your magnets screwed with each others polarity. Put the stir bar right on the magnets and see if the stir bar sticks to both sides at the same time, or if it is pulled towards one side or the other, if so, this may be the problem.

 

[Seabee John]

Here is a bit of help for you all. I've made several home made stir plates and have found that when the magnets on the fan are closer to the center, the bar gets tossed. If you increase the distance between the magnets on the fan (and they must be on an exact center axis) the magnet does not get tossed. Try placing a nickle between the magnets when you glue them on. Then remove the nickle after the glue sets.

 

[flyangler18]

I'm having the same issue with my stirplate, and it's a bit frustrating.

I have a feeling that the magnets aren't strong enough.

 

[broadbill]

Another possibility...one I've come across using stirbars/plates in the lab.

What does the bottom of your container look like? When there is a hump in the middle of the bottom of your flask/beaker (from the glassblowing I assume) the stirbar is forced to spin on top of it. However as it spins it can slide off the hump causing the stirbar to be thrown. Damn near impossible keeping it on balanced on the hump and spinning.
Hope this helps.

 

[conpewter]

I've read one of the best ways to do this is glue a 2" steel disk on your fan, and then just use the magnet's magnetism to hold it to that disk so you can move it around. Also if you are using something like a hard drive magnet you may want to use only one magnet centered.

 

[Brewers Hardware]

I've read one of the best ways to do this is glue a 2" steel disk on your fan, and then just use the magnet's magnetism to hold it to that disk so you can move it around. Also if you are using something like a hard drive magnet you may want to use only one magnet centered.

I've built and sold almost 70 of these now on eBay and the NB forum. Using a hard drive magnet is the way to go because it lets you only worry about one magnet and works great with a 1 -1/8" bar. You don't need to glue any steel to the hub, every fan I've used so far has already had a steel insert in the hub and the magnet sticks to it for positioning.

It's very important to have the bar spinning as close to its axis as you can get it, which isn't always easy because the stir bar will 'center' itself to different areas of the drive magnet. You need to drop it several times to search for the true magnetic center of things. Turn the plate on as slow as you can and look to see if the bar is being dragged rather than being spun, adjust the drive magnets accordingly.

Do not store the stir bar on the magnet and never store several stir bars together. As mentioned, this will cause them to lose their magnetism and cause inconsistent results. Try a few different length bars with your magnet setup, even a 1/8" difference can make all the difference. I've been using 1 1/8" X 5/16" octahedral bars with a ring and even though they can clatter a little, they have proven the best results in 1 & 2L flasks and 1G jugs for me.