Tight Arse Stir Plate

[Screwtop]

If that is just with water, you may be in trouble when you start growing the yeast. The liquid may become viscous enough for the fan to run out of grunt and stop (I have had this happen with a 60 mm stir bar in 3L starter).

But AFAIK, as long as the yeast is being agitated, you don't need a big ass whirlpool.

Might throw the stirbar into a whammy but i don't think you would stop the fan, maybe disengage the magnetic drive is about all. Besides, you only want the stirplate running to aerate the wort for good yeast growth, then turn it off, don't aerate the fermenting beer and risk oxidation if you want to pitch a nice clean starter. I turn the stirplate off as soon as there is a good krausen formed, fermentation keeps going and finishes out all by itself, thats when I refrigerate.

 

[schooey]

...maybe disengage the magnetic drive is about all.

Yep.. which is what happened, it was just sitting there with the stir bar centred, making an ear piercing whirrrrrr noise. I kinda thought that was the same as stopping the fan...

 

[hockadays]

I forgot the initial test photo with my new flask. Oh yeah. I'm going to grow up some german lager yeast just to check out the performance..

 

[SJW]

I simply substituted a higher rated pot (500 Ohm 3W wire-wound). It's been running for 2 years with regular use. The 500 Ohm pot gives a pretty good range of control over the magnet. The controller option seems the 'correct' way to solve the problem but there is no reason a properly sized series pot won't do the job.

I know I should just shut up and say nothing, but you was right LC. The POT stopped today. So I went to DSE and got a 500 Ohm 3W wire-wound job. If GH reckon his is still going strong that good enough for me.

Steve

 

[Fents]

Cue Lethal - I Told you SO!

ahhh well steve was worth a shot, you didnt hurt or mame yourself so its all good.

 

[LethalCorpse]

I don't need to say I told you so, but it's always nice to be proven right. Good on you for telling us, Steve.

Even the 3W pot won't be happy at the higher end of speed, but it should last much longer than the 0.25W. If/when it fails, or you become unhappy with the non-linearity, we'll help you through the process of building a proper one. I do hope it doesn't though - you've mucked about with this enough.

 

[SJW]

Dumb question time, as I am no Lectronic wiz are these Pots under more strain when turned down low or when running the fan flat out?

Would it help to change the power supply unit to a lower output type, say 9v or similar?



Steve

 

[LethalCorpse]

There's a peak point for the "strain" you're referring to (the power that the pot has to handle) close to the full speed of the fan. Check the graph that I posted a few pages back. There's a point at which it crosses over so that the power it has to handle is within the rating. The curved line is the power it has to dissipate, and the green slope is the power it can handle. The x axis is the resistance, with top speed being on the left. For a 3W pot, the crossover point is much further to the left than for a 0.25W pot, but there's still a range at the top end where you're pushing the pot too hard.

 

[LethalCorpse]

This is what it looks like for your situation, assuming your fan is rated to 200mA (my first chart was 300mA), again assuming the fan is a constant resistance, which it's not really. See how it's still over the rating until you get to about 100ohms? The maximum power is 0.6W, but at that point the pot can only handle 0.1W. Unfortunately, all your control is in the region where you're overpowering the pot - see how the current (blue curve) drops away up to about the 100ohm mark, then flattens out, meaning you get no real speed adjustments past that point.

All of that said, the 3W pot will be much more robust than the 0.25W, and will cope with the flogging much better. They generally underrate these things, so it's probably more like a 5W pot. Going down to 9V would improve matters, but would lose even more control.

 

[tynian]

I just wanted to say thanks to LC for the little circuit that he posted.

I just made it up this arvo and it works a charm. $5 worth of parts and 10 minutes work, could not be easier.

Rob.

 

[SJW]

So now I got it working do you leave it spinning for the entire time the starter is fermenting? and how fast should I have it going. With a bit of patience I can get 2 litres going so the vortex goes down to the stir bar, but thats obviously too fast, I guess it only needs to be just ticking over?
I went and got 2 25mm dia rare eather magnets as I was gaving trouble keeping the bar centred but these were no beter than the 4 (2 per side) 10mm dia rare eather ones. I did find that having the magnets on the outside of the washer (max away from each other) and going to a smaller 45mm stir bar works better. With large volumes of water its still a bit tricky to get it going without throwing the bar to the outside of the flask. Smaller flasks and water volumes work better.

Steve

 

[Simon W]

....
see how the current (blue curve) drops away up to about the 100ohm mark, then flattens out, meaning you get no real speed adjustments past that point.

If a 50R Pot was connected up as a Pot (Potentiometer) instead of a Rheostat there would be linear control, problem is the power is even worse, so no win.

I'm really struggling to understand why people aren't using the LM317 circuit?

Cons:
none?

Pro's:
Linear control.
No power issues.
Not much more difficult to build.
Almost half the price of a 3W wirewound.

Also, it should be easy enough to modify with a couple of extra resistors to provide min and max speed range.
That is, if you find that you never use the higher speeds, or that the lower speeds don't have enough oomph(fan stops) then dial in so you have full control over the useable range. This would probably get the circuit to about the same price as a wirewound.

 

[LethalCorpse]

I just wanted to say thanks to LC for the little circuit that he posted.

I just made it up this arvo and it works a charm. $5 worth of parts and 10 minutes work, could not be easier.

Rob.

My pleasure mate. Did you build the LM317 or the PWM driver?

 

[LethalCorpse]

If a 50R Pot was connected up as a Pot (Potentiometer) instead of a Rheostat there would be linear control, problem is the power is even worse, so no win.

I'm really struggling to understand why people aren't using the LM317 circuit?

Cons:
none?

Pro's:
Linear control.
No power issues.
Not much more difficult to build.
Almost half the price of a 3W wirewound.

Also, it should be easy enough to modify with a couple of extra resistors to provide min and max speed range.
That is, if you find that you never use the higher speeds, or that the lower speeds don't have enough oomph(fan stops) then dial in so you have full control over the useable range. This would probably get the circuit to about the same price as a wirewound.

It would cost $0.76 to do this, 0.38 if they're both the same resistor.

EDIT: actually, you only need to add one resistor, to set the min. The max is set by your choice of the fixed resistor and pot. It's a little more difficult to explain how to do this, so if anyone does want to, let me know.

 

[therook]

My pleasure mate. Did you build the LM317 or the PWM driver?

I'm going to make the trip to Jaycar tomorrow and buy the parts for the LM317 cct, doesn't seem as complex as your other cct LC

Thanks for your efforts

Rook

 

[tynian]

My pleasure mate. Did you build the LM317 or the PWM driver?

I built the LM317 with a switch for on/off.

This would have to be one of the simplest yet effective circuits i have come accross.

Rob.

 

[Screwtop]

So now I got it working do you leave it spinning for the entire time the starter is fermenting? and how fast should I have it going. With a bit of patience I can get 2 litres going so the vortex goes down to the stir bar, but thats obviously too fast, I guess it only needs to be just ticking over?
I went and got 2 25mm dia rare eather magnets as I was gaving trouble keeping the bar centred but these were no beter than the 4 (2 per side) 10mm dia rare eather ones. I did find that having the magnets on the outside of the washer (max away from each other) and going to a smaller 45mm stir bar works better. With large volumes of water its still a bit tricky to get it going without throwing the bar to the outside of the flask. Smaller flasks and water volumes work better.

Steve

Heres my finding, there'll be plenty of others. Used to leave on the stirplate continuously Steve, but had probs with infection like results in the beers, reason - oxidised wort. I use yeast nutrient in the wort and give a squirt of oxygen for 20 sec then start the stirplate, when the wort reaches a good krausen turn off the stirplate. I use a tiny 30mm bar which works well, natch, the outer circumference of one rotation is smaller, end of the bar travels less distance in one rotation so less resistance. If you use a small torch to look through the sides of your flask, it's much easier to see fermentation activity in the wort with yeasts that don't form much of a krausen.

Screwy

 

[LethalCorpse]

I built the LM317 with a switch for on/off.

This would have to be one of the simplest yet effective circuits i have come accross.

Rob.

It sure is. Its only real downfall is the limitation on the minimum speed that the fan will go to when being driven by a constant voltage. If that speed is lower than the minimum speed you need for the stirplate, it wins hands down.

 

[LethalCorpse]

I'm going to make the trip to Jaycar tomorrow and buy the parts for the LM317 cct, doesn't seem as complex as your other cct LC

Thanks for your efforts

Rook

Don't forget I changed the resistor values a few posts later because Jaycar don't have 20kohm pots. use 680ohm and 5k pot.

 

[SJW]

Heres my finding, there'll be plenty of others. Used to leave on the stirplate continuously Steve, but had probs with infection like results in the beers, reason - oxidised wort. I use yeast nutrient in the wort and give a squirt of oxygen for 20 sec then start the stirplate, when the wort reaches a good krausen turn off the stirplate. I use a tiny 30mm bar which works well, natch, the outer circumference of one rotation is smaller, end of the bar travels less distance in one rotation so less resistance. If you use a small torch to look through the sides of your flask, it's much easier to see fermentation activity in the wort with yeasts that don't form much of a krausen.

Screwy

Thanks mate. I think I started with 70mm stir bars and keep taking them back and getting smaller ones. I have a 45mm one now and it works good. I might take back the 55mm one and get a 30mm. I bet the 30mm bar looks small in a 2 litre flask? I think the trick is not to have the thing running flat out, just enough to keep it moving. It's a shame I have 4 full kegs at the moment otherwise I would love to give this a crack on some yeast. I am guessing it may perform a little different in yeast slurry rather than water too!

Steve