Stir plate troubles

[cnelsonplumber]

Hi hope everyone had a great Xmas :drunk:

Just finished (once I can get it to work) my "Stir Plate" which looks like this:

The magnets are Neodymium Disc Magnets 20x2mm and the stir bar is 50mm long.

Speed control on the fan is excellent but no matter how much I vary the distance between the magnets, the bar flies off to the side of the 1000ml conical flask. :wha:

I have varied the distance from the flask to the magnets from 1mm to 20mm and have settled at around 5mm although I think the problem is the length of the stir bar or the distance between the magnets.

Is anyone else using a 50mm bar? If so, have you spaced the magnets on 50mm centres? My magnets are currently "blue tacked" until I sort this out but I can't get much above 40mm centres without the magnets rattling around the box.

Any help would be much appreciated. :

I was expecting this to be the easy bit after making the speed controller! :shock:

 

[smdjoachim]

change the voltage going in to slow the fan down.i use a phone recharger of 5v and it works fine

 

[cnelsonplumber]

Hi

Thank you for the reply but I can slow the fan down until it stops, pretty much as soon as it starts to spin the stir bar flies off.

 

[keith1664]

After much fiddling about I ended up with my magnets further apart apart and a good 25mm below the flask (though I did go a bit OTT and stack 2 20x3mm magnets either side!) I'm using a 25mm stirbar.

 

[cnelsonplumber]

Thanks Keith. :thumb:

I have ordered a 25mm X 8mm bar from Fleabay.

Will put this project away for a week until it arrives. There is a very real danger it will be consumed by Lego if i don't!

 

[screamlead]

I found that my stir bars were also spinning off track too. Then i sussed it with a multi voltage thingy once i reduced the voltage to 9 volts it works perfect including changing speeds. :thumb:

 

[evanvine]

A hard drive magnet, model train controller, 25mm stirbar and gap of about 5mm between the magnet and stirbar.