Stir Plate not stirring

[Stevorino]

Hey guys, I made a stir plate and it's not quite working...here are some observations:

1) The fan with mounted magnets won't start unless I give it a push...even so, it won't spin at lower velocities...I think I may have gotten too small of fans.

2) The stir bar will not truly connect with the magnets on the fan through the pyrex glass. When the fan is rotating, the stir bar just sorta sits there and vibrates.

Any ideas?

 

[hammer one]

Can you show us a pic? That might help us figure it out

 

[MSUConrad]

First, did you pull the magnet off the harddrive plate? You just want the little magnet peice. Second did you put a rheostat knob on it? If so, and your fan won't spin, Take it out of the circuit.

Also, I use cell phone chargers for my power source (already DC). I have found that some are more powerful than others, so you may want to try out different ones.

Lastly, take your stir bar and magnet and rub them together for a minute or two. If they are even slightly repelling each other, it will never spin.

And as hammer said, pics would help.

 

[MNBugeater]

Couple issues I had and resolved...

1) Make sure the magnet is VERY centered on the fan hub. If it is even slightly off center and traveling in a circle rather than spinning in the center you stir bar will 'travel' as opposed to spin.

2) Rheostat...it sounds like you arent using a rheostat. If the fan needs some assitance starting and then your stir bar just vibrates, it is likely spinning too fast. You need to be able to slowly accelerate the fan.

+3 on 'Pics would help'

 

[Stevorino]

I'll post pics tonight.

 

[Stevorino]

Pics posted -- I posted the second one to compare the size of the fan to my hand-- I'm afraid i may have cheaped out on my fan/powersupply/magnets...

 

[NewBrew75]

Definately looks like too small of magnets, especially if you have them mounted to the under side of the fan. Maybe too small of fan also. If you point the stir bar end at one magnet, it should attract. The same end of the stirbar should push away from the other magnet. It looks like you have processor fan, not a case cooling fan. Get the 80 mm size fan if bigger magnets don't work.

 

[Duckfoot]

It looks like you have processor fan, not a case cooling fan. Get the 80 mm size fan if bigger magnets don't work.

I say +1 on this for sure... Those proc fans don't have a lot of torgue in them...

 

[yemu]

if the fan doesn/t start without pushing it, the current is probably too low. also you need some rheostat/voltage regulator, you could try to use somethig like this:https://www.elara.ie/products/detailsfull.asp?productcode=EQP52181

 

[MNBugeater]

Yup...too small of a fan and at least in my tests, you'll want the magnets centered on the hub rather than on the outside of the hub.

This is in the gallery. I just searched 'stirplate' and found lots of good examples.
This one has the right sized fan and the magnet centered in the hub.
Credit to forum member 'BeerCanuck'

And another great example from forum member 'wild'. If you can get access to some old computer hard drives, this is the magnet you can get...free.

 

[Stevorino]

Just bought a pair of 80mm fans online...let's hope they work

Any suggestions on where to acquire better magnets if that is a problem too?

 

[NewBrew75]

Just do a google search for "rare earth magnets". I ordered some online, but then found some at the hardware store close to me before I received my ones that I oredered. The size you need varies according to your setup. The ones that I use on my plate are (cylindrical) 12x3 mm, and they work great, but they're not too far from the surface, about a quarter inch or so.

 

[MNBugeater]

Just bought a pair of 80mm fans online...let's hope they work

Any suggestions on where to acquire better magnets if that is a problem too?

Take them out of old hard drives. Do you have an IT department at work? They usually have old drives to be destroyed or thrown. You can get great magnets out of those. Most homemade sitrplates use them. The pictures in my previous post show what they look like and where to place them.

Here is where they are located in the hard drive.