Problems with Stir plate project

[WhirlingBastard]

Hello all,

So I went ahead and built my stir plate this weekend but I did not have a good outcome.

I used the computer fan with the magnets from the hard drive. Both positive sides on the same side of the fan. I have a variable 5V power supply. I am also using the large stir bar from NB. I mounted everything in a cigar box. There is a 1/2 inche between the magnets and the top of the box.

With all that said, all my stir bar does is vibrate. Even if I set the flask on top on the fan it just vibrates more. No whirlpool effect at all.

See pictures attached.

What gives?

 

[bsay]

Put the stir bar, in the flask with some water, and manually turn the fan, does it work that way? How long is the "long" stir bar? Those magnets look way farther apart than any stirplate I've ever seen. Try putting them closer together?

 

[WhirlingBastard]

My stir bar is 2 inches long with a center ring to spin on.

 

[knowltonm]

Do you have a small stir bar, the 1"? My 2" bar won't budge with a 9V 300mA power supply when it's in the flask, but the 1" works great. I also only have 1 magnet centered on the fan, but I don't know if that would work for your 2" magnet, your magnet is about 1/2 the length of mine...not sure how I got lucky enough to find a big one. I also have somewhere around 1/2 inch from the top of the fan (not the magnet) to the top of the box (the outside). I don't know what orientation you'd want for the magnets because I only needed 1, but have you tried flipping those around?

Also, not to hi-jack the thread, but mine has been having issues not starting. I hear a high pitch whine almost and it goes nowhere. I hold another strong magnet above it for a split second and it starts right up. I'm stumped...but going to a stronger power supply from an old router that died.

 

[Yuri_Rage]

You need one north pole and one south pole facing up.

 

[ebeer]

I've had the best luck using just one magnet, centered on the fan motor.

Onebeer.net :: Homebrew :: Stirplate

 

[faber]

I use the 1"; I have a 2" and it doesn't quite work.

For a power supply, I use an Radio Shack multiple voltage adapter.

The 1" bar works best on 6V; even up to 12V the 2" bar only shimmies and rolls. It does help to get the fan/magnets closer to the surface of the enclosure. Mine's about 1/8" below the top of the project box.

FWIW, I can do some big honkin' starters just fine with the 1" bar--give it time to build up. The 2" bar in retrospect was a waste of money, but what did I know when I ordered it? nuttin'

 

[Mirilis]

I had a similar problem with mine. The magnets actually worked better when i stacked the 2 on top of each other.

 

[tedski]

Remember that hard drive magnets have both a north and south pole on each side. They are similar to a curved bar magnet, not a disk magnet. The problem I had with stacking my hard drive magnets was that it was then too much pull and would lock up the fan motor's stator. I wound up ordering some disk magnets from McMaster Carr to be able to have one pole per side of the fan.

 

[david_42]

I think you need to reduce the clearance, 1/2" is way too much. My magnet is almost touching the lid. I mounted the fan with long bolts & kept adjusting it upwards until it worked right.

 

[NoNothing]

I found that getting the magnets as close as possible was important, but Im pretty sure Im at about 1/2" too. If your magnets arent that strong, small and whatnot, try stacking them like others are saying, just get the stir bar centered

 

[WhirlingBastard]

Thanks everyone. I'm going to try getting the magnets closer to one another and I grabbed a couple more to stack on the current one's.

I'm going to try everything to get the 2" stir bars to work since I bought 2 @ $9 a pop.

 

[jcb317]

i had the same issue with mine when i built it. I ended up stacking the 2 magnets and putting them in the center of the fan, worked like a charm. I would also try getting the fan closer to the flask as others have mentioned.

 

[tedski]

I just mounted two .5" x .190" 5.7lb pull disk magnets on a 1.5" fender washer. Works like a charm. I ordered McMaster-Carr part # 5862K63. I put them on the washer 1" apart on center. I have .5" nylon spacers, so minus about 1/16" for the washer and the thickness of the magnet, I'm about 5/16" from the surface. Let me know if anyone wants pics of my setup and I'd be glad to provide.

 

[WhirlingBastard]

I just mounted two .5" x .190" 5.7lb pull disk magnets on a 1.5" fender washer. Works like a charm. I ordered McMaster-Carr part # 5862K63. I put them on the washer 1" apart on center. I have .5" nylon spacers, so minus about 1/16" for the washer and the thickness of the magnet, I'm about 5/16" from the surface. Let me know if anyone wants pics of my setup and I'd be glad to provide.

I would like to see pictures. You are 0.3125 from the top. I'm very close at 0.5

Last night I got two very strong magents out of a different hard drive and the magnetic pull I feel on the top of my cigar box is strong. BUT...again the stir bar just vibrates. This time a lot more with the new magents.

I went ahead and ordered the smaller (1") stir bar that everyone seems to think will help. Get's here Friday.

 

[tedski]

So, I did some tests last night with various stir bars and this thing spins a 1", 1.5" and 2" fast enough that I can't get to full speed before its thrown. Even with the 1" stir bar, I get a funnel that winds up touching down on the stir bar and dispersing bubbles everywhere.



More here...

 

[amishland]

i think you should stack them and put it in the center. I bet you a HB that it will spin the 2"er just fine.

 

[knowltonm]

Not with those magnets...you won't do too well with one pole in the center

Edit: oops, I was looking at the regular magnets in the pic. Magnets out of a harddrive sure.

 

[Homercidal]

I have mine set up just like your first pics. Works fine but starting the fan too fast sometimes doesn't get the bar to start. If I start slower and then ramp up, it works good. I think that having 2 poles on each magnet might allow the pull to get past the bar, and the one behind it to pull it back before the bar can actually get started.

I haven't messed with mine much since I first built it, and I used a cut-off nail for a stir bar, but that is my experience. I now have a real stir bar and plan to use it soon as I can and we'll see what happens. I also used a radio shack multi-voltage adapter and I think I remember it working best at 6V.

 

[DutchK9]

I made a similar setup and have the same problems. I have found that the 2" stir bar has to be in the middle of a flat bottom flask when you start the fan. Start it up real slow and gradually get it up to speed. As soon as the stir bar starts spinning, back the speed down to about two thirds full speed. This seems to work for me, but it does take several tries to get it going.