120v stirplate problems

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Budzu

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Hi all! I'm starting to brew alot more lagers and wanted to finally make a stirplate. Yeast is key.
I am attempting to use a 120v fan in my build. I would like to prepare starters of sizes from 1-2 gallons. I assembled this little thing from a 3 speed caged desk fan, and had the brilliant idea of using a standard light dimmer to control the speed. Evidently that wasn't so brilliant as the motor burned out all of a sudden after running for about 10 minutes.
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So for now I am scrapping that idea and using a very large powerful DC computer fan, with a variable voltage wall wort. I can now select between 6, 7.5, 9, and 12 volts.
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Works great but I still need a larger fan with more juice if I want to stir a small carboy. I need help at this point... I would like to use this fan motor:
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Now I need a way to control speed. The dimmer switch is bad. not sure why but it will fry ac motors. Is there something that will let me accurately control the speed of an AC fan? I've seen the 3 speed fan controllers at Home Depot and other hardware stores, but they are a bit pricey and will not allow precision control. Can anyone advise me in this endeavor? Thanks in advance and cheers!
 
I'm no expert, but after making a few for my friends and myself...

I'd Ditch the crazy fans and just get a big computer case fan. They come in very large sizes, are made to go forever, and can be used with components readily available at Radioshack.

Epoxy a large fender washer (or better yet something similar in lighter plastic) to the top of the fan. Then epoxy a thin piece of large diameter (3-inch maybe?) PVC pipe to the washer or plastic piece, and glue your magnets onto the opposite sides of the pipe. You should end up with something similar to this, but scaled up. Then you can use a power supply and potentiometer from Radioshack, and follow the tutorials on this forum.
 
Also, remember you don't have to have a huge stir bar just to keep everything agitated. A huge vortex is cool looking but completely unnecessary. So you're just trying to keep everything mixed up. I would guess that you could get by with a three or four-inch stir bar even a 1 or 2 gallon starter. (I wouldn't know because for a starter that large I usually just make a lower-gravity beer and pitch onto the yeast cake.)
 
Catt22 made one using a 120VAC muffin fan (yup, they're not all DC) and a light dimmer and a block of wood glued on top of the fan with some rare-earth magnets embedded in the wood. The photos are down (flickr) but it can be done. Perhaps he can chime in or you can send him a PM
 
I can get the pics back up if anyone is interested. I've built about 20 of these for friends and they are all running and perfroming well. I'm putting a few more together today and I will take some photos of the build in progress to post as well.
 
It must have been something about the particular fan I used, perhaps the built-in variable speed and voltage combined with the light dimmer, but it fried fairly quickly. I'd love to see the components you used successfully Cat.
In the meantime, the 12vdc is working well for 2L size for me with HD magnets. Waiting on some different size n52 disc magnets to arrive. Doggage that post was very helpful, I'm taking the spacer idea for sure.

Can't wait to try this out with some WLP 830!
 
try a ceiling fan speed control switch, some look just like a dimmer for a light, but they are made to vary the speed of the motor
 
Here ya go:

Basic Components:
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10" X 10" x 1/4" Plexiglass (for platform)
120 AC 120mm muffin fan (aluminum frame/ball bearing motor)
Rotory Dimmer Switch
Cleat Bulb Socket
3/4 dia x 1/4" Rare Earth Magnets
3/4" Oak Board
3 ft 18 ga lamp cord
lamp cord plug end
4 ea 1/4-20 x 4" flat head machine screws (stove bolts)
4 ea 1/4" flat washers
12 ea 1/4-20 nuts
4 ea rubber baby buggy bumpers (used as feet)
1 40 watt vanity light bulb
crimp type electrical connectors-various

Assembled
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Operating
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The light bulb functions as a resistor and it is wired in series with the motor. It effectively reduces the current to the motor and increases the dynamic range of the dimmer switch. The higher the bulb wattage the more power is delivered. I'm using a 40 watt bulb for this unit, but a different wattage may work better with other fan/magnet/dimmer switch combinations. Usually a 25 or 40 watt bulb works best. I can post some more pics if needed.
 
That's great Catt, thank you for posting that! Aha a light bulb resistor.. Genius!

What is the rated wattage or voltage/amps on that fan you have? Do you match the wattage with the bulb? Or work below the limit?

Couple other details if you don't mind: Are the magnets mounted INTO the wood or atop it? What kind of epoxy/glue?

Thanks again Catt
 
It must have been something about the particular fan I used, perhaps the built-in variable speed and voltage combined with the light dimmer, but it fried fairly quickly. I'd love to see the components you used successfully Cat.
In the meantime, the 12vdc is working well for 2L size for me with HD magnets. Waiting on some different size n52 disc magnets to arrive. Doggage that post was very helpful, I'm taking the spacer idea for sure.

Can't wait to try this out with some WLP 830!

AC motors don't really like running at a reduced voltage. That is probably why you fried the first one. I see people that 'seem' to get away with it, but......

AC motors can be controlled via frequency to a small degree from my understanding.
 
The fan is rated at 22 watts. A lot depends on the strength of the magnets and the power of the fan motor. The fans vary a lot from brand to brand. The distance between the magnets and the platform is another factor. The stir bar against the bottom of the flask creates resistance. This frictionional resistance is greatest on initial start up and is substantially less once the bar begins to spin. What this means is that you must overcome the initial resistance, but less power is needed to maintain speed once it's moving. If the magnets are too close to the platform, the friction is quite high and once moving the bar can spin out of control. Some trial and error is required to get this right and as mentioned, it depends on the type of magnets used, the type of fan etc. I start with a 25 watt bulb and if that does not provide enough power, I replace it with a 40 watt bulb. One or the other will usually work well with most fans.

The magnets are mounted in the wood disc. I used a forstner bit to bore the holes with precision. This is the most tricky part of the assembly. The magnets need to be aligned and centered with care. Here's how to do it. Draw a line on the wood before you cut out the disc. Make three punch marks with an awl or a brad nail. Measure these carefully. Now, using a 1/16" bit, drill all three marks all the way through the board. Use these as the centers for boring the magnet pockets. The center one will be used for the hole saw pilot bit. Enlarge the center hole to about 3/16". It's best to use a drill press for this. Using a 3/4" forstner bit, bore out the magnet pockets. Do this slowly and carefully so that the magnets are flush with the disc surface when installed.

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I use 3M 77 spray adhesive to fasten the disc to the fan and to hold the magnets in the pockets. The advantage of this adhesive is that it will hold well, yet it allows you to move the disc to get it centered. Once you have it well centered, a few drops of Super Glue down the center hole makes it somewhat more permanent, yet you can still remove the disc later if necessary. Also, the reason for boring the pilot holes all the way through the wood is so you can easily push the magnets out later and start over if you did not get everything well aligned and balanced. The spray adhesive is forgiving in this respect too. You can separate the disc from the fan without damaging the fan if need be. Use a straight edge along side the disc and spin the fan while centering the disc. The disc must be very well centered to minimize wobble and vibration. I used a 3-1/4" hole saw to cut the disc, but the excact diameter is not critical. The oak disc acts as a spacer to insulate the magnets from the fan motor. The strong magnets can interfere with the motor magnets if they are too close. The heavy oak disc also works as a flywheel and has a stabilizing effect keeping the speed steady through minor line voltage fluctuations such as may occur when another applicance on the same circuit is switched on.
 
to hermit's post:
Is that how a light dimmer switch works? reducing voltage?

The built in speeds on the fan were: 6a 120v, 3a 240v, and 8a 120v. Not sure which speed the 240v was, but it had some transformer or resistor built in on that line. I tried using the dimmer with each of those speed settings. I need to learn more about this stuff before fiddling like an idiot :p
 
to hermit's post:
Is that how a light dimmer switch works? reducing voltage?

The built in speeds on the fan were: 6a 120v, 3a 240v, and 8a 120v. Not sure which speed the 240v was, but it had some transformer or resistor built in on that line. I tried using the dimmer with each of those speed settings. I need to learn more about this stuff before fiddling like an idiot :p

It's been a while, but as I remember it, the SRC (silicon controlled rectifier) cuts the peaks off of the sine wave.

I was lucky. The company I worked for paid for my education and I used that feature quite a bit.
 
Nice info Catt! You're a huge help, thank you again. I want to use all of these ideas you posted, but one added feature I would love to have is the ability to easily remove and replace the magnets with different sizes and different spreads. I did order 5 different sized stir bars (1/2" thru 2 1/2") and several different size magnets for starter vessels from 1 liter to 2.5 gallon. I'll be thinking of ways to do this today. Any ideas? maybe multiple magnet seats drilled into the same wooden disc? maybe some kind of screw fitting with interchangeable and differently configured discs?
 
Happy to be of help. Building it with interchangeable magnets won't be easy, but I'm sure it could be done some way or other. The stir plate shown will easily stir any flask up to 5 liters. I've use a one gallon glass jug with no problems at all. The real limitation with the one pictured is the size of the platform. Build it with a bigger platform and add some additional outrigger supports and I'm sure you could stir a 6.5 gallon carboy. This one will work well with either a 1.5" (38mm) or 2" (51mm) stir bar. I prefer the 2' bar as it seems to stir better at a lower speed. The magnets are spaced for the 2" bar, but work just fine with the 1.5" bar as well. I have found that it's best to space the magnets according to the bar length for best performance. I've experimented with a lot of different magnet sizes and bar lengths and eventually came to the conclusion that the arrangement pictured works best. I've also come to the conclusion that gentle stirring with a larger bar is better than thrashing the yeast at high speed with a smaller bar. Another thing I have learned is that a strong vortex is not always indicative of efficient stirring. IOW, a strong vortex is often created by the center portion of the fluid moving much faster than the outer portion. You can see this effect when you initially add some food coloring to the water. A larger bar keeps the entire volume moving at a more even rate, but does not create as deep a vortex. The food coloring disperses more rapidly with a larger slower moving stir bar. I was a little surprised to see that happening.
 
http://picasaweb.google.com/soundspicasa/Stirplate?authkey=Gv1sRgCIjT6LWg-PWLdg&feat=directlink

There is how i did mine. The metal washer on top allows me to swap/add/remove magnets as well as evening out the magnetic field. My original design had the magnets glued directly to the pvc pipe. This resulted in the bar being randomly thrown off. So I glued a large washer to the top of the pvc pipe instead and just laid the magnets on top of the washer without gluing them down. Last starter i did ran for ~3 days without it being thrown off.
 
Works great but I still need a larger fan with more juice if I want to stir a small carboy. I need help at this point... I would like to use this fan motor:
PICT0012.jpg

Now I need a way to control speed. The dimmer switch is bad. not sure why but it will fry ac motors. Is there something that will let me accurately control the speed of an AC fan? I've seen the 3 speed fan controllers at Home Depot and other hardware stores, but they are a bit pricey and will not allow precision control. Can anyone advise me in this endeavor? Thanks in advance and cheers!

I made this from a bathroom fan motor and a medium duty dimmer:
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It does a carboy iif needed, and 2 gallons without any trouble.

Mega_Stir_Plate1.JPG

Hope that helps...
 
try a ceiling fan speed control switch, some look just like a dimmer for a light, but they are made to vary the speed of the motor

Exactly! One of the electrictions should time in, but there\'s a big diff in how a dimmer and a fan speed control work (one is resistive and the other inductive, I think). Go to Lowes or HD and price them. Dimmers are dirt cheap. Fan speed controls cost $20-$50.
 
try a ceiling fan speed control switch, some look just like a dimmer for a light, but they are made to vary the speed of the motor

I tried using a ceiling fan speed controller. Didn't work for me. Did it work for you? I did, however, get excellent results using a cheap rotary light dimmer switch. No overheating problems with the motor or the switch and I've had several in operation for a number of years. Not even a hint of a problem so far.
 
Well my build was a success! I used the 12vdc fan I pictured earlier, and found a nice little wooden coaster from a hobby shop for 50 cent. Used a forstner bit to make holes for 2 7/8" by 1/2" neodymium magnets driving a 2.5" stir bar (thanks for the ideas here Cat22). These are the magnets and bar Sudbuster used in his great thread "Mega Stir plate". Thanks Sudbuster! The coaster is held to the fan by the immense strength of the magnets, and a small bit of 3m spray adhesive, which indeed is strong bond but removable. I'm also using the 2.5 gallon ankor hockings Montana jar. I was very pleased that the 12volt fan is able to drive the bar through that dense of glass.

For power, I'm using a variable voltage wall wort.
3v and 4.5v do nothing, 6v gets the fan started, 7.5v creates 3-5 inch deep vortex, and 9v makes a ridiculous raging vortex that won't throw the bar. 12v throws it immediately.
Right now it is stirring 1.5 gallon of my WLP 001.

Thank you guys so much for all this help, it was really invaluable! Especially Cat22 and Sudbuster. I will post pics later this evening of the current starter I am running. This was not a cheap stirplate to build compared to others here (factoring all components), but it is the strongest and most compact I have seen ever!

Cheers all, pics coming
 
btw that is approximately 500 billion cells of wlp 001 that I pitched into 5 liters of 1.035 wort. It has been used for 2 previous batches and has been sitting cold in my fridge in plain water for 1 month since harvesting last.

It kicked into action within 1 hour of pitching into this starter! Nice!
 
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