Home Made Stir Plate Not Working

[jceg316]

I made my own magnetic stir plate and it works: the fan spins round. However I've tried dropping the stir bar in a jug with water and putting it on the stir plate. When I turn on the fan the stir bar spins for a couple of revolutions then stays where it is.

I can post pictures if needed of the build.

Thanks in advance

 

[GermLish]

More Power

Try it with water in it (lubrication).

What happens if you put the magnetic stirrer direct on the fan?

 

[jceg316]

I did try with water in the jug. I made it out of an old PC PSU so I can't put the stir bar on the fan as there is a grate in the way. But the magnets stick, I did try before putting it all together.

Could the magnetsbe too weak though?

 

[GermLish]

if the fan doesn't stop it surely the magnetic field is to weak.

Either get more powerful magnets or try to bring the magnets closer to the stirrer. Also make sure the magnets on the fan are not to far away from the centre/parallel to the stirrer poles.

 

[jceg316]

if the fan doesn't stop it surely the magnetic field is to weak.

Either get more powerful magnets or try to bring the magnets closer to the stirrer. Also make sure the magnets on the fan are not to far away from the centre/parallel to the stirrer poles.

In those diagrams what do those numbers mean by the magnets? Are they a type of magnet?

Thanks for your help.

 

[GermLish]

seems so yes, but I don't know or care as I have already bought some and I have 3d printers I can use. Just need to finish other projects.

I just wanted to show you the magnetic field and how to configure it.

The end of the magnets should be in one line.

 

[Dutto]

The bearings on the fan have some movement.

It is therefore possible that the fan "lifts" when it turns, moves upwards towards the stir-bar magnets, catches on the bottom of the flask and stops.

I cut the hole in the top of the box to prevent this from happening ... :thumb:

... and I also have a couple of very thin magnets that can be placed on top of the ones shown in the photo to act as "shims" so that the magnetic fields are as near to the stir-bar as possible, without touching the bottom of the flask. :thumb:

 

[Fil]

good points above,

also ensure any vessel you test the magnet in has a flat bottom,

the best stir bars to use with a diy stirplate are the large triangular bars,

some sort of speed control of the fan helps too as the fan can spin way too fast,

my take is very basic, simply a fan blu-tacked onto the psu borrowed from the brewday pumps.

i used a large brass washer to widen the gap between magnets too a bonus is that its extra mass slows down the fan too

 

[jceg316]

thanks for your replies. The fan itself moves around fine, it's just the magnet doesn't. I have a pot in the circuit so I can control the speed of the fan. No setting works.

F*ck it I'll just buy one!!

 

[jceg316]

Actually I'll try a different magnet. I found an old HDD and have Amazon primed the right screwdriver so I can get into it.

 

[Chippy_Tea]

Have a look on ebay for - Neodymium Magnets

Even small neodymium magnets have a surprising amount of magnetic force and they are capable of lifting in excess of 1,000 times their own weight. A neodymium disc magnet weighing only 2 grams can lift a steel block weighing over 2,000 grams! ... Two neodymium disc magnets 10mm ...

 

[GermLish]

Have a look on ebay for - Neodymium Magnets

http://www.ebay.co.uk/itm/111622148275

 

[strange-steve]

Actually I'll try a different magnet. I found an old HDD and have Amazon primed the right screwdriver so I can get into it.

Probably been cheaper to buy the magnet than the screwdriver.

 

[jceg316]

I have neodymium magnets, but something is not working.

It isn't that much cheaper to buy the magnets. I got a cheap screwdriver set. And now I will have magnets and a screwdriver set.

 

[Fil]

have the magnets opposite poles up , and distance them equally from the centre on the same line through the hub centre, any deviation can cause a wobble that can throw the stir bar out of its spin.

if you can capture the stir bar by the magnets when you sit a flask with some water on it, start by slowly dialing up the speed, if the stir bar starts to spin but gets thrown off your magnets are probably not aligned, But.. Steel screws etc used to secure the fan at its corners can also throw a spanner into the works as the stir bar will also have an attraction to them, so use synthetic or non ferrous fastenings

also...

use a spacer to maintain the distance between the magnets while glue/epoxy sets.

position the magnets about the length of your stir bar apart so the attraction between the magnets and stir bar is at its peak.

 

[jceg316]

Thanks for all your help. I used the magnet from a HDD and did a better job of aligning it and now I have something very useable. Not perfect but it does the job!