How to build a stir plate for less than ten quid

[merrydown]

Thanks Stange Steve, I finally got all my parts today and built the beast.

I opted for a 3 litre flask which I felt would be handy for larger starters and it makes a cool vortex in the three inches or so of water I have tried so far.

It's a genius bit of simplified engineering which I would never have figured out without your template.

I am looking forward to using it for my first lager starter in a couple of days :)

 

[brumbrew]

I'm sure. Long ago in this thread I said I used a cpu fan with some magnets. A jar of science and a USB 5v thingamjig. Cost me next to nothing.

 

[strange-steve]

@merrydown glad it was helpful :hat:
It should easily get a good vortex in 3L, though I've found I have to throttle back a bit on the speed to keep the stir bar stable. Just a little dimple in the surface is enough to keep the yeast in suspension anyway.

 

[Tunabeast]

Is there a consensus on the size of magnetic stir bar for a 3L flask - would a 25mm bar do it do you think?

Also, does anyone have a live link to a PC fan they've used - having read the thread it sounds like some are hit and miss.

 

[Oneflewover]

I really must get on and build one of these..... Got a plastic roses container from Christmas put by

 

[BeerCat]

Is there a consensus on the size of magnetic stir bar for a 3L flask - would a 25mm bar do it do you think?

Also, does anyone have a live link to a PC fan they've used - having read the thread it sounds like some are hit and miss.

I tried a few and settled on an 80mm fan with 2 round magnets on each side. Works better with 2. I use a round 25mm stir bar like this as the others are too noisy.

 

[Drunkula]

You definitely get better magnetic coupling with separated magnets compared to the hard drive type. If you're sticking them on yourself attach them to your stir bar because it'll give you the best spacing and the right polarity either side.

I haven't even put mine in a box yet and put a plate over the top and some blu-tak on it to stop the cafetiere I use as a flask from sliding about.

I did a yeast starter with some yeast I'd had in the freezer for a month in glycerine solution the other day and it worked phenomenally well. I'm never going to crop from trub or krausen again and always store it from starters.

 

[Oneflewover]

I upgraded my stir plate from the soap box to a chocolate box. I found after a few uses the structural integrity of the soap box was rather compromised. It was sagging a little in the middle meaning the magnets were rubbing on the inside making a very irritating sound. Also it wasn't waterproof, so I had concerns about the starter overflowing onto it. I also couldn't get rid of the lavender smell from it which was annoying when trying to have a smell of the starter. The new one isn't as pretty but much more sturdy and made of plastic so should last a bit longer.

Hello @strange-steve. Could you please tell me how you mounted the fan on the bottom of the tub / top of the stir plate? It doesn't look like you have drilled through it to accommodate the mounting bolts. I have a very similar 'post-christmas' container. Concerned that if I fix the bolts in place through the plastic of the container the flask will be sitting on the bolt heads. Cheers!

 

[strange-steve]

Hello @strange-steve. Could you please tell me how you mounted the fan on the bottom of the tub / top of the stir plate? It doesn't look like you have drilled through it to accommodate the mounting bolts. I have a very similar 'post-christmas' container. Concerned that if I fix the bolts in place through the plastic of the container the flask will be sitting on the bolt heads. Cheers!

Actually I did put the mounting screws through the top, so the flask is sitting on the screw heads. I just put a little bit of blue insulation tape over the screw heads so they wouldn't scrape the glass. And the screw heads are very shallow so it only raises the flask about a mm off the top of the tub, the magnets are more than strong enough to cope with that.

 

[Oneflewover]

Actually I did put the mounting screws through the top, so the flask is sitting on the screw heads. I just put a little bit of blue insulation tape over the screw heads so they wouldn't scrape the glass. And the screw heads are very shallow so it only raises the flask about a mm off the top of the tub, the magnets are more than strong enough to cope with that.

Thanks Steve. I couldn't think of a way around drilling through it, good to know it works fine like that. :hat:

 

[matt76]

Great instructions @strange-steve , stir plate now built for around £15

One question - how the chuffing hell do you stop the magnetic bean flying off?

 

[strange-steve]

Great instructions @strange-steve , stir plate now built for around £15

One question - how the chuffing hell do you stop the magnetic bean flying off?

Slow it down a bit. You don't need a full on tornado in the flask, a little dimple on the surface is enough

 

[Drunkula]

how the chuffing hell do you stop the magnetic bean flying off?

What sort of magnet(s) have you used? If they're separate make sure that they're spaced based on the stir bar size and have the right polarity. I attach them to the stir bar and push them underneath to mark where to glue them.

And try and get the magnet as close to the lid as possible. When I was using a hard-drive magnet I mounted it on a stack of sticky pads.

 

[matt76]

Slow it down a bit. You don't need a full on tornado in the flask, a little dimple on the surface is enough

Got it, thanks

"Mr Sulu, one quarter impulse power"

 

[matt76]

What sort of magnet(s) have you used? If they're separate make sure that they're spaced based on the stir bar size and have the right polarity. I attach them to the stir bar and push them underneath to mark where to glue them.

And try and get the magnet as close to the lid as possible. When I was using a hard-drive magnet I mounted it on a stack of sticky pads.

It's virtually identical to the OP, except I used a Celebrations box instead of Roses

I stuck the neodymium magnets and the bar magnet together while I glued the former onto the fan - so everything should be right polarity and in the ideal position.

I think I'm just giving the fan a bit too much welly!

 

[Dutto]

...........

One question - how the chuffing hell do you stop the magnetic bean flying off?

As previously pointed out, a dimple in the surface will suffice; but if you buy a set of these you should find one that fits perfectly across the magnets and can therefore go to a much higher rpm.

https://www.amazon.co.uk/dp/B07D39JMBB/?tag=skimlinks_replacement-20

Using different diameters also gives you a lot more flexibility.

 

[Tunabeast]

Ordered my bits to build one of these - hope they arrive in time for brew day on Saturday!

 

[Snoop]

I know homebrew is mostly about DIY but having built a few stir plates and then bought this. You can't really argue for £20. Works really well even with my 3litre flask.

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/192803187355

 

[matt76]

Question:

How do you know when it's started fermenting? (not that I'm impatient or anything )

I've got my starter and yeast in a flask running nicely on the stir plate.

Would we expect to see some krausen forming on the surface once it's started fermenting, as you would in the FV, or if you just left it without stirring.....

Or is the stir plate mixing all that stuff in?

 

[matt76]

I know homebrew is mostly about DIY but having built a few stir plates and then bought this. You can't really argue for £20. Works really well even with my 3litre flask.

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/192803187355

Other than the delivery time, yes, I'm inclined to agree with you