Tight Arse Stir Plate

[Ross]

Hi Ross,
how much liquid did you have in this flask? Sorry, cannot see very well from the picture B)

Just under 1.5L - It's a 2L flask, or was before I dropped it

Cheers Ross

 

[Franko]

**** Smith has some cheap enclosures available on special for $4.92 big enough to house a larger fan 140mm x 140mm
just picked one up



http://www.dse.com.au/cgi-bin/dse.storefro...duct/View/H2508

 

[Jase]

Hi All,

Sorry to bring up an old topic. But I'm in the process of building one of these stir plates. Bought the same case as Franko, and a pair of the oblique-spheroid hematite magnets from Jaycar.

During testing, I placed the fan on the bottom of the case, no spacers, and put the other magnet in a coffee plunger with a flatish bottom, I was getting some vortex, and the unit was working ok. I decided to raise the fan with some 15mm spacers, to create more vortex, but the unit is noisier (vibration etc), and sometimes the magnet in the coffee plunger won't even spin. I've even tried spinning it by hand, but there seems to be too much magnetic force resistance (if there's such a thing). I didn't think that you could have the fan too high. I thought the closer the magnets are together, the better the unit would work.

The reason why I posted, is because I'm ordering a flask from Livingstone today, and am wondering whether I'm better off ordering a stir bar as well (instead of using the magnet in the flask). Any thoughts??? :blink: :huh:

What size flasks should I be looking at? 2 litre seems to be the go in this topic.

Cheers,
Jase

 

[Andyd]

Grab stir bars as well - they're inexpensive and work well.

 

[KillerRx4]

Stir bars for sure. Forget the oblique thingo magnets. Theyre just begging to break your new flasks.

You will have to find a different magnet to mount on the fan for the stirbar as the oblique magnets poles are different. I have had most success with magnets from old hard drives.

 

[Ross]

I find the oblique magnets work great, they even work in containers where a flat stirbar wont - but they are quite powerfull, so I guess putting them too close together maybe putting undue upward strain on the fan.
The 2L flask is a good choice. So as not to damage the flask, I use a handheld magnet on the outside to slide the oblique magnet down the inside with.

cheers Ross

 

[goatherder]

So as not to damage the flask, I use a handheld magnet on the outside to slide the oblique magnet down the inside with.

cheers Ross

You don't even need another magnet - a lump of something steel will do. I used a spanner to hold the magnet while I pitched the yeast.

 

[crozdog]

Jase,

I'd recommend grabbing stirbars as well as a 500ml & 2l erlenmyer flasks from Livingstone's if you're puttin in an order. The freight will be the same & you will get a smaller flask to use to step up your yeasts on the way to 2l.

Beers

Crozdog

 

[Chilled]

I started off with the oblique magnets and tried to use one of the stir bars from Livingstons with it. It failed dismally.
The stir bars from Livingstons have an North and South pole at each end of the bar as you would imagine with any bar magnet. However the oblique magnets have the North and South poles in the centre of the oblique section with one on top of the other. When used with the stir bar you will find that one end of the stir bar will be attracted to the centre of the oblique magnet and the other will not be attracted to anything. As a result the stir bar does not spin around its centre and goes crazy. Either stick to how Ross does it with the second oblique magnet as your stir bar or purchase rare earth magnets (mine are 15mm diameter and 5mm thick) to use with the stir bars.
Also as Sosman quoted somewhere get the stir bars without the pivot ring. The ones with the pivot ring make a lot of rattling noise. :angry:

On another note I burnt out a couple of variable resistors in an attempt to adjust the speed of the motor. Then it dawned on me that the power supply plug pack was the sort that had different voltages that you could select. Now all I do is select different voltages on the plug pack to vary the speed of the motor and have got rid of the "pot" altogether.

Chilled

 

[Trough Lolly]

...So as not to damage the flask, I use a handheld magnet on the outside to slide the oblique magnet down the inside with.

cheers Ross

I wish I'd read that utterly logical idea before my wife dropped a spheroid magnet into my new empty 2L flask leaving a bullseye and crack in it! :angry:

I'm getting frustrated trying to spin ANYTHING with these hermatite magnets - I think I'll give them to the kids and buy a couple of button magnets....

TL

 

[Trough Lolly]

I started off with the oblique magnets and tried to use one of the stir bars from Livingstons with it. It failed dismally.
The stir bars from Livingstons have an North and South pole at each end of the bar as you would imagine with any bar magnet. However the oblique magnets have the North and South poles in the centre of the oblique section with one on top of the other. When used with the stir bar you will find that one end of the stir bar will be attracted to the centre of the oblique magnet and the other will not be attracted to anything. As a result the stir bar does not spin around its centre and goes crazy. Either stick to how Ross does it with the second oblique magnet as your stir bar or purchase rare earth magnets (mine are 15mm diameter and 5mm thick) to use with the stir bars.
Also as Sosman quoted somewhere get the stir bars without the pivot ring. The ones with the pivot ring make a lot of rattling noise. :angry:

On another note I burnt out a couple of variable resistors in an attempt to adjust the speed of the motor. Then it dawned on me that the power supply plug pack was the sort that had different voltages that you could select. Now all I do is select different voltages on the plug pack to vary the speed of the motor and have got rid of the "pot" altogether.

Chilled

Great post Chilled! :super:
You just confirmed some of my problems - I'm off to buy some new magnets.

 

[laurent]

I started off with the oblique magnets and tried to use one of the stir bars from Livingstons with it. It failed dismally.
The stir bars from Livingstons have an North and South pole at each end of the bar as you would imagine with any bar magnet. However the oblique magnets have the North and South poles in the centre of the oblique section with one on top of the other. When used with the stir bar you will find that one end of the stir bar will be attracted to the centre of the oblique magnet and the other will not be attracted to anything. As a result the stir bar does not spin around its centre and goes crazy. Either stick to how Ross does it with the second oblique magnet as your stir bar or purchase rare earth magnets (mine are 15mm diameter and 5mm thick) to use with the stir bars.
Also as Sosman quoted somewhere get the stir bars without the pivot ring. The ones with the pivot ring make a lot of rattling noise. :angry:

On another note I burnt out a couple of variable resistors in an attempt to adjust the speed of the motor. Then it dawned on me that the power supply plug pack was the sort that had different voltages that you could select. Now all I do is select different voltages on the plug pack to vary the speed of the motor and have got rid of the "pot" altogether.

Chilled

Great post Chilled! :super:
You just confirmed some of my problems - I'm off to buy some new magnets.

Hi,

I mainly agree with this. However, if you keep both oblique magnets together and stick them to the fan, it will help have north/south poles further apart and stabilize the stir bar. Plus it will ensure the poles are on a plane parallel to the stir bar. Now a bit of blue-tac is more than enough to stick the magnets on the fan, helps for repositionning later on. I've been stirring this way twice already 24h straight and it is working great. Maybe the weight on the fan is a bit high and the magnets a bit too strong, but it works.

To vary the speed, I've build a simple voltage regulator as in here:Voltage regulator, first diagram. You'll have to replace R2 with a 1kOhm pot to get voltage from 1,5V to 12V. I think it may be better than a variable resistor, because the fan seems to draw a lot of current and heat up the pot real hot. I use an old laptop power pack to get the 17V input.

I have a 4cm stir bar w/o pivot and a 7cm pivot stir bar. Both works great.

Cheers,
Laurent

 

[Trough Lolly]

Dumb question: are you suggesting that the oblique magnets sit side by side on the fan, or stacked on top of each other!?!?
I'm assuming you mean side by side...yes, bluetack is enough for me too...

TL

 

[Doc]

One of the guys from Brewboard has posted a small video of his stirplate in action.
Wouldn't nornally be that interesting except for the groovy labware he has his starter in.
Video link here

Beers,
Doc

 

[laurent]

Dumb question: are you suggesting that the oblique magnets sit side by side on the fan, or stacked on top of each other!?!?
I'm assuming you mean side by side...yes, bluetack is enough for me too...

TL

Hi TL,

yes, I meant side by side, laying flat. Easy.

Laurent

 

[Trough Lolly]

Cheers Laurent,
I guess it's worth a try this weekend....

 

[laurent]

Cheers Laurent,
I guess it's worth a try this weekend....

Hi TL,

how did it go last week end? As a final thought, I would not recommend anybody to use the Jaycar oblique magnets.
Pro:
- Strong

Cons:
- Too heavy
- North/South poles are on the side rather than on ends
- Radiation not from the middle, so when adjusted, the weight balance is off and the fan shakes a lot

I would have saved lots of time buying calibrated neodymium magnets for a few more $ ...

But the final result is still good :lol:

Cheers,
Laurent

 

[Jase]

I find the oblique magnets work great, they even work in containers where a flat stirbar wontt

cheers Ross

I decided to try the oblique magnet in a flat bottom coffee plunger, dropped an old dried yeast in and ran the stir plate for 24 hours. The magnets worked beautifully, whisper quiet and spun perfectly. After turning the stir plate off and letting the yeast drop, I ended up with about 15-20mm of yeast in the bottom of the plunger. Stoked.

So I decided to order the flasks, without the stir bars. h34r: The flasks arrived today from Livingstone, althought the 2 litre one was a cheapy, not the Simax one I ordered, :angry: Livingstone are fixing that problem. Anyway, I thought I'd test out the new flask, magnet and stir plate. Carefully, placed the magnet into the 2 litre flask, added some water, magnet started to spin, but after 30 seconds, the magnets just stopped, but the fan in the stir plate was still spinning. Can't work out why. I decided to try the 500ml flask instead, carefully placed the magnet in the flask, somewhat harder, and the magnet won't spin at all. I'm at a complete loss as to why the stir plate and magnet were working perfectly using the coffee plunger, but not in the flasks.

Any advice,

Cheers,
Jase

 

[The Scientist]

Heres an idea for the players;

Managed to pick up a power supply out of an old 386 computer. All I did was turn the fan around in the case and replace the fan cage with a piece of glass from a picture frame. Then attached the magnets and there you have it. The power supply has 4 other 12v power outlets so I can drive another couple of stirrers off this one box.




As Im not really that great at electronics this was easy to set up and works a treat.

The stir bar is the flat type and in the photo its in a cut down bottle cap. I don't need to use it any more as I have just relanced the fan magnets and its now quite and spins perfectly.

Thanks to all who have given me the inspiration to delve into this project, next up will be the grain mill from a washing machine motors given to me by the neighbours.

 

[goatherder]

nice work the scientist! smart thinking, power supply, fan and mounting box all in the one unit. very neat.