Stir Plate Challenges!

[skepace]

So I built a cigar box stir plate from the introductions I found online. It all works but I think it spins too fast because the stir bar can't keep up.

I installed a 25 hon rheostat to control the speed but it still seems too fast. I used 2 really small button rare earth magnets (Radio Shack closing prices) and made sure they were centered on a piece of cardboard on top of the fan.

The fan is 12V and so is the power source as it is an old router power supply.

How can I slow it down or should I use larger button magnets? My stir bar is 1" long.

Thanks for the help.

 

[stpug]

Slow it down? Use a lower voltage wall wart (9v or 6v even).

 

[skepace]

Slow it down? Use a lower voltage wall wart (9v or 6v even).

Would that fix the stir bar from flying around?

 

[stpug]

Would that fix the stir bar from flying around?

Not necessarily, but certainly too fast of spinning can cause the stir bar to be thrown. The question is what is causing YOUR stir bar to be thrown. Determining what exactly is causing the stir bar to be thrown, in your case, is the stage that you're at. I assume you affixed the radio shack magnets with opposite polarities pointed upwards so that they attract both ends of the stir bar.

Other variables that I have been cause thrown stir bars is:
-rare earth magnets are too far from stir bar
-rare earth magnets are too close to stir bar (true)

If you are extremely close then you can easily add distance to test that scenario. I use small square of cardboard to add distance when needed.

 

[tonyj30]

i,m building one at the moment,and have got some small strong magnets
but all the stirplaats i,v recently seen that worked well have big magnets.i,v stopped the build and am changing to a old hard drive magnets
this won,t help with the speedcontrol, but ! have you looked at ebay for a ventilator controler print ?
i made a list of all the parts for a controler,and then found one ( and many ! ) on ebay for 2,50 $ each. 4 euros free shipping to EU
anyway succes

 

[skepace]

Well I added card board and it didn't change the performance of the stir bar. Maybe I will use a 9 or 6v power source first and then if not try getting larger magnets.

Any other suggestions?

 

[skepace]

Can you use ceramic magnets or just rare earth magnets? My stir bars moves just fine on top of the box but when I place it in there beeker it doesn't.

Could the box be too thick? I really like the box and all of the work I already placed into it.

 

[eddiewould]

You're starting the stirplate with the bar already in place, right? (just checking)

 

[skepace]

You're starting the stirplate with the bar already in place, right? (just checking)

Already in the beeker? Yup.

 

[skepace]

Any other suggestions as to why this is working in the beaker?

 

[flars]

Can you borrow a two inch stir bar to test the performance of the longer length?

 

[agentgreen]

I had to spend a bit of time making sure my magnet was exactly centered before it stopped throwing my bar. I'm using a hard drive magnet so it's a bit different but I would look down into the flask and see if the bar was centered over the middle of the fan, test it and make minor adjustments until it was perfectly centered. At that point my bar stayed put no matter what speed.

 

[skepace]

Can you borrow a two inch stir bar to test the performance of the longer length?

I can probably go by the LHBS as they have them. Would that magnet be stronger? I might try a thinner box if that doesn't work.

 

[cyberbrew]

I had to spend a bit of time making sure my magnet was exactly centered...

Same here. I ended up using velcro to attach the magnet to the fan which worked out really well as minor adjustments are a snap.

 

[skepace]

Same here. I ended up using velcro to attach the magnet to the fan which worked out really well as minor adjustments are a snap.

I might really get a hard drive magnet. Might work better.

 

[bob1852]

Is the bottom of your flask curved? Many are....and that can affect stir bar performance.

 

[skepace]

It is flat until the edges.

 

[cyberbrew]

I might really get a hard drive magnet. Might work better.

Yep, that's what I'm using. Works like a charm.

 

[skepace]

Got a hard drive magnet from another home brewer who repairs PC's. So, how the hell can I get it off the plate?View attachment ImageUploadedByHome Brew1429142925.391660.jpg

 

[stpug]

A couple pairs of pliers gripping both ends of the metal plates and bending backwards (away from the magnet) is how I do it. Once you get some room under the magnet then a screwdriver or butterknife will free them up completely.

 

[skepace]

Thanks! Worked great! I will make the magnet change tomorrow and hope it works better.

 

[schematix]

I used 2 of these on each of my stir plates: https://www.kjmagnetics.com/proddetail.asp?prod=D82

At less than a buck each, much less hassle than extracting hard drive magnets.

This makes a great stir bar extracter too: https://www.kjmagnetics.com/proddetail.asp?prod=D6C

 

[skepace]

Well I would say the hard drive magnet fixed it! Don't use rare earth magnets is my suggestion. View attachment ImageUploadedByHome Brew1429213568.752127.jpg

 

[schematix]

Nice vortex

 

[skepace]

Nice vortex

Thanks! Thank you to everyone who helped!