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Old 12-20-2009, 03:12 PM   #1
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Default 120v stirplate problems

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.


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.


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:

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!



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Old 12-20-2009, 04:55 PM   #2
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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.



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Old 12-20-2009, 05:00 PM   #3
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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.)

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Old 12-21-2009, 03:44 PM   #4
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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

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Old 12-21-2009, 05:28 PM   #5
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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.

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Old 12-21-2009, 06:58 PM   #6
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Please do, I'd like to see this!

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Old 12-22-2009, 12:59 AM   #7
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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!

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Old 12-22-2009, 02:02 AM   #8
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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

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Old 12-22-2009, 03:08 AM   #9
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Here ya go:

Basic Components:


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


Operating




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.

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Old 12-22-2009, 02:44 PM   #10
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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



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