Stir Plate Motor Options?

I made my own Stir Plate based on a computer fan as many here have done. I'm now doing 11 gallon batches and of course larger starters. I've never had very good luck with the computer fan, but for smaller starters it was tolerable. But just won't work for the bigger starters needed for larger batches.

So anybody have any suggestions as to a better stir plate motor? My current unit is 12V DC that I would like to simply replace the motor in if someone has a better motor choice than computer motor. I've tried several of them and just not had good enough luck to make another worth the effort. Although I have messaged with Derrin from Brewers Hardware and he had a good suggestion. He suggested that I use a PVC cap to raise the magnet up off of the fan motor a bit to lesson the magnetic coupling to the motor. I'll give that a try.

But in the meantime looking for motor suggestions. I would not be opposed to scrapping the current unit and starting over with something known to work better than computer motor.

Here's my version using a 120mm 12V DC muffin fan:





There are more than a few variables to deal with when putting together a DIY stir plate. Sounds like you may just need to get a bigger fan.

Looks like you got the motor I need. I'm surprised that it will start spinning at slow speed. That seems to be my biggest problem. If I crank up the speed enough to get the motor spinning rather than locked up, it throws the stirbar.

RonRock said:

Looks like you got the motor I need. I'm surprised that it will start spinning at slow speed. That seems to be my biggest problem. If I crank up the speed enough to get the motor spinning rather than locked up, it throws the stirbar.

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Heard somewhere throwing of the stir bar has to do with magnet placement. I would like more details because I'm planning on making one soon.

What I've found with mine is that the magnet that I glued onto the fan, actually pulls the fan blade tight to the fan motor because of the magnet in the motor itself. This causes it to have too much drag to start under load until the voltage (speed) is cranked up. Then with a smaller starter it is controllable. But even with a small starter once the yeast start to grow there is more drag and more issues keeping things working.

Basically not enough torque with these computer motors. I'll look into a larger one. Unless someone chimes in with a better alternative.


Edit, it don't actually pull the hub tight to the motor. Just a bit tighter causing the hub a bit more drag.

RonRock said:

Looks like you got the motor I need. I'm surprised that it will start spinning at slow speed. That seems to be my biggest problem. If I crank up the speed enough to get the motor spinning rather than locked up, it throws the stirbar.

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The key is using the light dimmer to control the wall wart. The modern dimmers are basically simple PWM units. They function by rapidly switching the current on and off. What this translates to is when it's "on", the fan is getting full power and this equates to more torque on start up.

You may have your magnets too close to the stir bar. This can create too much friction between the stir bar and the bottom of the flask. Once the stir bar starts moving, the friction is dramatically reduced and the bar will often spin out of control. Try increasing the gap between the magnets and the stir bar. This may require some repeated trial and error to get right. The fans come in wide variety of sizes and power. I recommend using a 120 mm fan with ball bearings.

The magnet alignment and balance is critical for best performance. You can sometimes compensate for poor magnet spacing, alignment and balance by using a smaller stir bar. The smaller stir bars are less prone to getting thrown.

Interesting thoughts on speed control. So do you have your 12v from the wall wort going directly to the fan motor?

Here is what my stir plate is built from,

http://sites.google.com/site/tysoncolby/pcb

RonRock said:

Interesting thoughts on speed control. So do you have your 12v from the wall wort going directly to the fan motor?

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Yes, the wall wart is hooked up directly to the fan motor. I've built more than a few of these units over the years and this design works best so far.

Certainly worth a try.

I have a 120V pancake fan. You think that would work with a dimmer? Don't get any easier than that.

Anything I need to look for in a dimmer switch?

RonRock said:

Certainly worth a try.

I have a 120V pancake fan. You think that would work with a dimmer? Don't get any easier than that.

Anything I need to look for in a dimmer switch?

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I used to use 120v AC muffin fans with the light dimmers and it works OK, but the DC fans work better. I've found that the cheapest rotary style dimmer switches work best. I get mine at the local Do-it-Best Hardware store. Beware that not all muffin fans are equal and they won't all operate the same way. This goes for both AC and DC fan motors.

Sounds like I better get a 120mm 12V DC muffin fan. You don't happen to have a link to a place I could buy one like yours? It is obviously working very well.

Appreciate the help with this. It's crazy how something so simple can be so frustrating!

RonRock said:

Sounds like I better get a 120mm 12V DC muffin fan. You don't happen to have a link to a place I could buy one like yours? It is obviously working very well.

Appreciate the help with this. It's crazy how something so simple can be so frustrating!

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I buy the fans as Micro Center for about $12. I bought a couple of steps up from the very low end versions. Look for ball bearing motors or something other than sleeve type bearings. I don't have a link, but I might be able to take a pic of the box one came in if I can find it. I think the brand name was Manhattan and it's a 120mm size.

Here's some pics of the fan that's working well for me. It's the same as the one shown in the videos:

Thanks again. That gives me some direction to start looking.

RonRock said:

Thanks again. That gives me some direction to start looking.

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Glad to be of some help. Post back when you get it up and running. If you use a 2" stir bar, space the magnets at 1-1/2" center to center. It's best if you have the magnets and stir bar in hand to check that spacing, but that's worked well on mine. That video with the gallon jug is using a 2-1/4" barbell style stir bar, but it's the same 1-1/2" spacing as with the 2" bar used in the 2 liter flask. I strongly recommend getting a pair of disc type rare earth magnets. I use 1/4" x 3/4" rare earth neodymium disc magnets that are rated at 19 lbs pull each. They are scary strong.

Catt22 said:

They are scary strong.

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Man you got that right. Those Rare Earth magnets are amazing.