Tight Arse Stir Plate

[Trough Lolly]

G'day all...
Thanks for the replies - here are some pics of the stirrer.
This is a shot of the wiring - power connect on the left and the pot on the right - wired up as per Pete and Jye's original specs...All soldered!!

Here's a shot of the unit with the magnet fixed to the fan - it's not perfect centre and makes a little bit of noise at full tilt but not enough to make the unit jump around...

Last shot is just from the front...note the larger case to sit a 2L flask on.

I'm beginning to think the pot is too small - you have to wind the pot almost completely clockwise to get any action out of the fan and then its only a few millimeters of play between flat out and nothing - and when I wind the pot clockwise, you get a very high pitched squeal which quickly drops in tone and then the fan starts to turn. Surely this isn't right???
Any ideas/suggestions appreciated - I cannot get the fan to turn slowly enough to allow the stir bar to keep pace with the magnet below - so is it a new pot or should I drop the voltage to the fan??? :unsure:
And just to make my day even better - I've cracked my brand new Schott 2L Flask so any info can only make this day better!! :blink: :angry:
Cheers,
TL

 

[Jye]

ah... ignore my last post, I was think you only had to turn a little bit to high speed... when its the other way around.

In that case a larger pot may help.

You may have a log pot which could explain why the control is sensitive, a linear pot should remove the sensitivity. To check look for an A (log) or B (linear) printed on the back of the pot somewhere.

 

[goatherder]

Instead of using a larger pot, which I think will make the sensitivity problem worse, I would try putting a 500ohm resistor in series with the pot. This will lower the supply voltage to the pot and allow it to supply 0-6V to the fan instead of 0-12V OR try a lower voltage power pack, maybe a 5V phone charger.

[post="129304"][/post]​

I was thinking of that - one of the link from sosman's page has some series resistance in before the pot. I'll do the calcs and see what I can work out. I was still going to stick with a 500 ohm pot - just a higher power rating to help keep the smoke on the inside.

 

[Trough Lolly]

...snip...
You may have a log pot which could explain why the control is sensitive, a linear pot should remove the sensitivity. To check look for an A (log) or B (linear) printed on the back of the pot somewhere.

[post="129313"][/post]​

I think you're onto something here Jye - stamped onto the back of the pot has a lower case "a" in a circle and beneath it:
ALPHA
B25K
followed by 4L3 in black on the bottom edge of the pot. The 1st pic I attached above shows most of those markings when you click on the image...I might take it to Jaycar and get them to confirm - I can always get a linear pot and some other larger 1K or better pots and experiment (it's easy once you know how to solder!!). I also have some lower voltage power units laying around the house - including one that works between 3 to 12 volts. I need to slow down the fan...
Cheers,
TL

 

[Jye]

...snip...
You may have a log pot which could explain why the control is sensitive, a linear pot should remove the sensitivity. To check look for an A (log) or B (linear) printed on the back of the pot somewhere.

[post="129313"][/post]​

I think you're onto something here Jye - stamped onto the back of the pot has a lower case "a" in a circle and beneath it:
ALPHA
B25K

[post="129340"][/post]​

I think the pot you have is linear 25000ohms (B25K), check it with a multimeter or get the guys at jaycar to do it. This is your problem since the resistance is too high until you have turned it all the way to the end. Replace it with a 500ohm and all should be sweet

 

[Trough Lolly]

It's off to Jaycar I go...Thanks Jye.

TL

 

[user 865]

TL,

the "squeal" you talk about from the fan is likley the fan trying to start up on too low a voltage/current. Some fans happily start on a wide range of voltages (even down to 40% of their 'rated' voltage) others struggle even at some 75% of their rated voltage. Usually, once spinning, the fan will happily slow down and keep running. The other catch is by introducing the resistor the current to the fan is limited and thus is more likely to stall. 500 ohms would be a much better size resistor as a first attempt.

I usually use a pulse width modulator (PWM) which pulses 12v to the fan so you get enough voltage to start the fan and the speed is then controlled by the pulse on-pulse off ratio. IF you dont mind the fan making a bit of noise, it is possible to have a virtual 0-100% speed range. I haven't looked at the modified phone charger circuit mentioned in this thread in much detail as I already have a circuit to acheive the same thing, but it might be along the same "concept".

Give me a call if you like and I can etch a board for the circuit for you (uses about 8 components so nothing too complicated).

Darryl

 

[Trough Lolly]

G'day all,
Well, Jye, you were right! It was a 25K pot and the Jaycar staff were a tad embarrased...I ended up getting a 500 ohm pot and they wanted to charge me for it until I reminded them that it was their mistake.
Anyways, it's now soldered in and the fan runs a lot slower and is much more controllable - once you get it spinning.
There is one problem left to sort out now - and that's the orientation / centering of the magnet over the fan. Even at low speed, the stirbar is not working as it should - it spins and then flicks off at a tangent and then spins back to the centre and out to a tangent, etc, etc. I'm also getting cavitation from the fan - which I didn't think was a problem, but it's obviously doing that because the large heavy magnet is not centred on the hub. I can see it's slightly off centre so I've carefully cut the magnet off the fan (I used 2 part epoxy and thought I'd be there all night with the stanley knife but it eventually lifted!!). Anyway, I'll draw some lines on the hub of the fan to help centre the magnet, check with the tape measure and refix the magnet to the fan and test before epoxying again.
And who said Friday nights are boring!!!
Cheers,
TL
P.S. Darryl - thanks very much for the kind offer mate - If I can't get this unit to work after re-centering the fan, I might just take you up on the kind offer to etch a board etc. Thanks...

 

[poppa joe]

TL
Has anyone thought about a Train Controller....Would it work...???? if so
Tell the Kiddies Daddy wants to play with it....
Cheers
PJ

 

[Jye]

TL
Has anyone thought about a Train Controller....Would it work...???? if so
Tell the Kiddies Daddy wants to play with it....
Cheers
PJ

[post="129528"][/post]​

As long as the voltage is about 12V.

 

[Trough Lolly]

As a result of stuffing around with the voltage all day, I now have all the DC power packs around the house in my possession - and boy, don't we have a decent collection of them?! Every bloody phone charger, answering machine unit, camcorder charger etc - I've got a slew of them on my workbench!!
TL

 

[Ross]

As a result of stuffing around with the voltage all day, I now have all the DC power packs around the house in my possession - and boy, don't we have a decent collection of them?! Every bloody phone charger, answering machine unit, camcorder charger etc - I've got a slew of them on my workbench!!
TL

[post="129535"][/post]​

I know the feeling TL - i bought one for my stir plate & then realised when I got home, that we have over a dozen redundant transformers i could have used <_<

cheers Ross

 

[Trough Lolly]

Yup....and when you're trying to measure the gap between the end of the rare earth elliptical magnet and the outer edge of the fan with a ruler - don't use the METAL tape measure! Grab a timber ruler from the kids and you've got a lot less 2 part epoxy to clean up...!!
I think I'll call it quits, grab a beer and watch the footy - and do the centering of the magnet in the morning!!
Cheers,
TL

 

[Trough Lolly]

TL
Has anyone thought about a Train Controller....Would it work...???? if so
Tell the Kiddies Daddy wants to play with it....
Cheers
PJ

[post="129528"][/post]​

//Totally unqualified wildassed guess follows//
I suppose it would - it depends on the output voltage and current. My old CB Radio transformer is a regulated 13.8V supply that can push a couple of amps under load - which is way above what the 12VDC 200mA fan needs...

Cheers,
TL

 

[sosman]

I'm also getting cavitation from the fan - which I didn't think was a problem

Hmmm, the fan is not supposed to be inside the wort.

 

[vlbaby]

I'm also getting cavitation from the fan - which I didn't think was a problem

Hmmm, the fan is not supposed to be inside the wort.

[post="129691"][/post]​

I think TL means vibration not cavitation.


vl.

 

[Trough Lolly]

Quite so - apologies for the Red October freudian slip!!

I think my problem may be with the distance between the magnet on the fan, it's centering on the fan and the distance between the magnet in the case and the stir bar - I bought a large case, big enough to comfortably sit a 2L flask and thus, its deeper than the smaller models - I have added some nuts to the bolts holding the fan in place so I can adjust it's height in the case, and thus bring the whole assembly with magnet closer to the underside if the top of the case.
If this cunning plan fails, I'll ditch the elliptical magnets and buy a couple of cheap bar magnets from Jaycar...
Cheers,
TL (who's off to Adelaide for a couple of days tomorrow - will be lurking in the vicinity of the Stamford Plaza bar!!)

 

[Damon]

Not sure what the Motorola motor driver circuit costs but as an option you could use either the top or bottom circuit of the attached to drive a fan up to 3A (3A might be a bit of overkill...). It uses a 555 timer to adjust the PWM applied to the fan and hence the speed for those that are electronically minded. This circuit can adjust from 0% to 100% drive.

Cheers,

Damon

View attachment stirrer.PDF

 

[goatherder]

I finally made it to dick smith to pick up the pot. I ended up grabbing the 500 ohm 3W wire wound job, I figured it would be pretty hard to burn that fella out. It's just wired up in series with the fan, easy as that. It works a treat.

Here's a pic, thanks to everyone who posted for your ideas and methods.

 

[Jye]

Nice one goatherder Did you have any problems with the magnet?

 

[goatherder]

Thanks Jye, your photos were a great help.

At first I couldn't work out why the fan wouldn't turn the magnet. The fan would start to spin but would just sit there and quiver. I think the magnet was interfering with the motor, so I stuck a 3/8" washer under it which made it go. I guess my fan didn't have a metal bit under the centre like some pics i've seen.

I was a bit lucky when I glued it all in, I must have got it almost centered. If I keep the speed low enough, the stirrer doesn't develop any precessional movement. I reckon if I want higher speed i'll have to raise the fan up a bit inside the case with some spacers. I should be OK without it though.

I ran it non-stop overnight in the 2l flask and it was still running happily this morning, with no signs of overheating. Now I just need to wait for the wyeast order to come in.

 

[andreic]

Hi all,

just went to Jaycar today to get those "oblique-spheroid hematite magnets". They are on special this month - $6 instead of $15.

Since the thread is titled "tight arse" I thought some others might be interested in a $9 saving...

cheers,

Andrei

 

[goatherder]

dammit, i only got mine two weeks ago

 

[laurent]

Thanks Jye, your photos were a great help.

At first I couldn't work out why the fan wouldn't turn the magnet. The fan would start to spin but would just sit there and quiver. I think the magnet was interfering with the motor, so I stuck a 3/8" washer under it which made it go. I guess my fan didn't have a metal bit under the centre like some pics i've seen.

I was a bit lucky when I glued it all in, I must have got it almost centered. If I keep the speed low enough, the stirrer doesn't develop any precessional movement. I reckon if I want higher speed i'll have to raise the fan up a bit inside the case with some spacers. I should be OK without it though.

I ran it non-stop overnight in the 2l flask and it was still running happily this morning, with no signs of overheating. Now I just need to wait for the wyeast order to come in.

Hi,

I did almost the same thing. Only, I glued the magnet to the fan using Blue Tac. Very strong and I can still move the magnet around to reduce vibration. Did you get the vortex up to the bottom of the jar? Sometimes when the speed is too high my stirrer jumps around and might break the jar. I suspect it might be too heavy. I'll try to find some real stirrers. Anybody has one spare for sale?

Cheers,
Laurent

 

[crozdog]

I pulled a few old hard disks apart over the weekend. Each one had 4 rare earth magnets for driving the arm to move heads over the platter. :beerbang:

I dunno if they were glued or spot welded onto the mounts, but a few minutes with a grinder (bench or angle) would cut the mounting plate back to the magnet.

I also reckon they were a good shape to mount on the top of the fans & as they are only a couple of mm thick, spacers might not be required between the fan body & the case.

Here's to tight arse brewing & creative recycling. :beer:

Crozdog

 

[goatherder]

Hi,

I did almost the same thing. Only, I glued the magnet to the fan using Blue Tac. Very strong and I can still move the magnet around to reduce vibration. Did you get the vortex up to the bottom of the jar? Sometimes when the speed is too high my stirrer jumps around and might break the jar. I suspect it might be too heavy. I'll try to find some real stirrers. Anybody has one spare for sale?

Cheers,
Laurent

Same thing happens with me when the speed gets too fast. I couldn't get the vortex going to the bottom without the stirrer getting shaky and threatening to break my shiny new flask. From what i've read it doesn't matter, keeping the yeast in suspension is the goal. A slow speed will be enough for that.

 

[Trough Lolly]

Same thing happens with me when the speed gets too fast. I couldn't get the vortex going to the bottom without the stirrer getting shaky and threatening to break my shiny new flask. From what i've read it doesn't matter, keeping the yeast in suspension is the goal. A slow speed will be enough for that.

Same here...and this is my problem - I keep blaming the magnet but perhaps it's something else? I find that the fan can only get down to a certain speed and then if I try to slow dow the fan any further, the whole lot comes to complete stop. The stir bar jumps around like I've put some voltage through it and I can't get a vortex. Oh and if you want to trash your 2L flask, let the missus DROP a hermatite oblique magnet into it, when the flask's empty... :angry:

Perhaps I need to solder in a couple of resistors in series between the power and the 500ohm trimpot?

TL the electrical numpty...

 

[Ross]

I get a vortex going using these magnets with quite a slow spin, I think being able to control the speed correctly is the most important part. The faster spin showers liquid everywhere, long before becoming unstable.



Cheers Ross

 

[bindi]

I have aquired the gear to make a stir plate now to build it

soon I will have enough yeast to take over the world :blink: .

 

[laurent]

Hi Ross,

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

Thanks,
Laurent

I get a vortex going using these magnets with quite a slow spin, I think being able to control the speed correctly is the most important part. The faster spin showers liquid everywhere, long before becoming unstable.

View attachment 7606

Cheers Ross