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Old 12-22-2009, 03:18 PM   #11
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Originally Posted by Budzu View Post
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.
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Old 12-22-2009, 03:52 PM   #12
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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.









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.

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Old 12-22-2009, 03:53 PM   #13
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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

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Old 12-22-2009, 04:00 PM   #14
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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.
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Old 12-22-2009, 04:06 PM   #15
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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?

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Old 12-22-2009, 04:32 PM   #16
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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.

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Old 12-22-2009, 05:33 PM   #17
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http://picasaweb.google.com/soundspi...eat=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.
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Old 12-23-2009, 02:38 PM   #18
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Default 110v AC stirplate

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Originally Posted by Budzu View Post
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!
I made this from a bathroom fan motor and a medium duty dimmer:

It does a carboy iif needed, and 2 gallons without any trouble.


Hope that helps...
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Old 12-23-2009, 03:18 PM   #19
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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
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.
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Old 12-23-2009, 06:19 PM   #20
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This is how I built mine. I went together really easily, and because of the washer, it is changeable down the road. It's pretty strong and can stir the powdered extract into the water, so it's super easy to build a starter in a beaker.

http://www.homebrewtalk.com/f51/pimp...-plate-152513/

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