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Old 11-09-2007, 10:08 PM   #141
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Alex -- it can be quite hard to get a bar to spin stably in a concave vessel, even on a professional stirplate. If I'm stirring large volumes here in lab, I always make sure to grab a flask with the flattest bottom available. Flasks vary from manufacturer to manufacturer. If you don't plan on heating your wort in your flask, you can substitute any glass vessel you want for use on your stirplate.

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Old 11-13-2007, 04:00 AM   #142
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OK So I have fallen back to a new approach after the 500MA power supply burned out. This is becoming more frustrating than anything else. But I will never give up.

I have come up with a new modified design, I have just orderd some of the PC fans kits form newegg mentioned in the post earlier, I am going to salvage one of the many PC Power supplies I have here at the house and I am going to the MAN STORE (aka Home Depot) and get some LEXAN (Plexi-Glass); maybe in some funky colors and put it all together. This will allow me to do the 2 - 5000ml flasks at once if I place the fans right. I envision it looking like a plastic brief case with fans. Plus I could some disco lights or something inside if I get real adventurous. I will post some pics this next week when I have it all put together.

Should be pretty cool.

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Old 11-13-2007, 10:52 PM   #143
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Quote:
Originally Posted by Scimmia
I'm building one of these (with just a few changes to the circuit) and have a quick question for anyone who has one. How far do you turn it up? From what I can tell, this design is capable of driving the regulator into dropout, which I don't like, so if you're only turning it up half way, I'll just change R1 to max out at a reasonable voltage.
Anyone reading this thread anymore that has one?
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Old 11-14-2007, 04:04 AM   #144
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I made a cheap stir plate as well. $7 fan and $3 pot from RS. Old cell phone charger and a magnet from a hard drive. I saw a lot of pics with two hard drive magents being used, but one is all that is required. If you use two, make sure both positive poles are at one end and both negative at the other, otherwise you end up with a weaker magnetic field. (Most flat magents have poles that go out the flat sides, so you have to use two - one with positive up and the other with negative up. Hard drive magnets have poles that go out the ends.)

The issue with only using one hard drive magnet is balance - single axis of symmetry. The trick is finding the center of gravity. The easy way is to put the magnet on top of a taut piece of thread the long way and try to pick up the magnet by balancing it on the thread. By trial and error, find the axis it balances on and mark this on the magnet with an extra fine tip marker. Then draw a line dividing the magnet in half the short way (measure, eye ball it, or use the thread again). The point where the lines cross is the center of gravity. I drew cross hairs on my fan at its center and lined up the lines on my magnet with the lines on the fan. Not a hint of wobble.

Made a cheap box out of 2x4s and a clipboard.

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Old 11-14-2007, 04:11 AM   #145
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Quote:
Originally Posted by Bearcat Brewmeister
The issue with only using one hard drive magnet is balance - single axis of symmetry. The trick is finding the center of gravity. The easy way is to put the magnet on top of a taut piece of thread the long way and try to pick up the magnet by balancing it on the thread. By trial and error, find the axis it balances on and mark this on the magnet with an extra fine tip marker. Then draw a line dividing the magnet in half the short way (measure, eye ball it, or use the thread again). The point where the lines cross is the center of gravity. I drew cross hairs on my fan at its center and lined up the lines on my magnet with the lines on the fan. Not a hint of wobble.
That's a fantastic way of getting the COG. I've tried balancing the magnet on a pencil. same idea... mark the COG
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Old 11-15-2007, 04:19 AM   #146
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Well I am not sure how to upload images on the forum. I look around for a pic place or something and didn't see anything. I am dieing to send a pic of the layout I have so far. I ended up with 1 magnet on each also. Works like a charm.

any help on how to upload images would be great.

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Old 11-15-2007, 06:00 AM   #147
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Quote:
Originally Posted by waterkc
Well I am not sure how to upload images on the forum. I look around for a pic place or something and didn't see anything. I am dieing to send a pic of the layout I have so far. I ended up with 1 magnet on each also. Works like a charm.

any help on how to upload images would be great.
I can't wait until you post your pics so I can see how yours turned out.
I ordered a 2" stir bar and a 2000ml Erlenmeyer last week, and they arrived
at about 5pm yesterday.

I have scavenged 7 hard drive magnets (one drive only had one), so I have
more than enough of those to get any size field that I want. I also have a ten
pack of rare earth magnets from Rockler Woodworking. They are 3/8" by 1/10".
I believe that I will use the hard drive magnets, but may change my mind yet.
The Rockler magnets are SUPPOSED to be for some refrigerator magnets for the wife.

I have two standard 80mm case fans, and one 120mm case fan to play around with also.
I also scavenged the power supply from an old AT form factor computer
case, and am trying to use that. It appeared to be way too powerful, ramping
the fans up to full speed instantly, and sending that pig of a stir bar flying. I
pulled out an old fan speed regulator, and that seems to be helping some,
but I am still having some trouble. With one of the 80mm fans, I glued on a single hard drive
magnet, and it just does not seem to grab the bar well. With the other, I have two
magnets stacked together, and they seem to grab the bar better, but they also seem to
be slowing down the fan considerable, even causing it to not start spinning at times.
I would really like to try the 120mm fan, but it will need to have a large washer added to it,
as I have seen done in some of the other plans on here, as the inner workings of the fan itself
are keeping me from placing magnets where I would like to.


I just got done drilling a piece of Lexan, putting screws down through it, with
some spacers, and clamping the fan on underneath, with two hard drive
magnets stacked together and fairly well centered. I have not had a chance
to test it yet.

The advantage to the old AT power supply, assuming that it is truly not too
powerful, is that it already has the pin connectors for the fan, so there is no
extra work needed, you just plug it in and go. My fan controller can also handle
up to three fans, so ONCE I get this thing working right, I will probably expand
it to handle at least one more fan. I have two 6.5 gallon primaries, and five
5 gallon secondaries, so it would be nice to be able to run two batches of yeast
at the same time.

Well, we will see what tomorrow holds.

Hopefully I can get this thing working. I have a batch of cider that is just finishing
its first yeast, then I am going to pitch a champagne yeast into it to take it the
rest of the way, and I really want to test this thing out with that yeast.
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Old 11-16-2007, 03:30 AM   #148
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Ok well I figured out how to upload images ( ya pay's your money and you take your chance's)

So here it goes, this is the overview of the hole setup keep in mind that I still need to clean up the wires and all.


Here is a shot of the fan controllers


and here we have the magnet in place



Yeah I am feeling pretty good at this point, hehe

I have a piece of Lexan and some sheet wood to build the case that is this weekend. So stay tuned for the finished product.

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Old 11-16-2007, 03:41 AM   #149
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Rabidgerbil, how did you stack the magnets, by gluing them together?

I had the same problem with the fan not spinning - the magnet pulled the fan down onto the motor real tight and wouldn't let it spin. If you look at my picture, you can see a piece of metal under the magnet. It was from the inside of the hard drive (magnet was attached to it). I ground it down to near the size of the magnet and now it shields the motor from the magnetic field. Washer would do the same thing.

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Old 11-16-2007, 03:57 AM   #150
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The one issue I do have is that one of the magnets is spinning fine and the other spins for a second or two then kicks off the stir bar. I am going to work on this a bit. As the first 30 tests it worked just dang fine on both. Hmm

any suggestions?

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