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DIY Magnetic Stirrer / Stir Plate & Bars

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#1 Hippie3



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Posted 17 April 2006 - 07:45 PM

A Magnetic Stirrer for Yeast Starters
By Peter Fitzsimons

What is a Magnetic Stirrer
A magnetic stirrer is a device that lets you stir a solution without having any contact between the stirring motor and the solution. What you do is add a small, sterilised stir bar into the liquid and sit the container on the magnetic stirrer. This is an ideal device for kicking off yeast starters in a short time.

Why use a Magnetic Stirrer
There are many of us that have yeast farms and want to step yeast up quickly from a plate or storage under sterile water, or even from a commercial yeast package.

A magnetic stirrer stimulates the yeast activity and helps you grow the yeast population rapidly. As an example, I stepped up from a partially swollen Wyeast packet to a 2 litre starter where the yeast had fully fermented the starter wort and flocculated in 24 hours.

What you need

You can build a magnetic stirrer very easily as all parts are readily available. You will need a soldering iron to connect a few wires together, but apart from that, the rest of the tools you will have in your shed. Like all projects, this can be done cheaply if you have access to old parts lying about.

An old computer fan is the ideal motor for the stirrer. I paid $5 for a new one, but you can always get one from an old computer.

The plug pack is one of the most expensive items on the list. There are some phone chargers that are suitable or maybe on that you have that used to run something in the cupboard. Just make sure it is rated between 8 and 12V DC @ 300mA or better. The fans use less than 3 watts of electricity. One of the have seen have draws 120mA and the other around 200mA, so a 300mA plug pack gives us a margin for error.

The parts that I used were

Qty Part Source Approximate cost

1 80mm 12V computer fan Computer shops, old PC’s $0 to $7

1 9 to 12V DC 300ma or better plug pack Jaycar - MP3006 $0 to $18

1 500 ohm linear pot Jaycar $1

1 Knob to suit above pot Jaycar, Dick Smith Electronics $1

1 Panel mount socket to suit plug pack Jaycar, Dick Smith Electronics $2

1 Screws to mount aluminium brackets inside case Hardware store or an old PC $1

1 Polycarbonate case 115 x 90 x 55 Jaycar - HB6218 $17

4 Screws 40mm long to mount the fan Hardware store $2

2 20 x 12 mm angle aluminium approximately 143mm long Hardware store $4

2 50mm magnetic stir bars Livingstone or other lab suppliers $4 each

2 70mm magnetic stir bars Livingstone or other lab suppliers $9 each

2 Bar Magnet - Size: 70 x 12 x 5 Jaycar - TH1874 $1

4 Rubber feet Jaycar, Dick Smith Electronics $1

The cost of unit will depend on how well you can source pieces, but I would expect that you can get all pieces (excluding the stir bars) for under $45

Assembling the stirrer
The following steps outline how to make the stirrer

Glue the two magnets together (N to N, S to S). Combining the two gives us a stronger magnet. I used liquid nails to bond them together. Once they are glued, put them to one side and continue with the other steps.

Make up two brackets using the angle aluminium to fit inside the case. These will be used to mount the fan. When you drill the holes in the brackets, drill them as close as possible to the angle join in the aluminium as this makes it easier to mount the fan. Screw the brackets into the case (you will need to remove it again, so don’t do the screws up too tight).

The holes for the potentiometer and socket can be drilled out now. Make sure that you have enough room for the pot to fit inside the case as some models are quite large and the corners of the case intrude inside.

Centre the fan in the case and mark holes in the brackets so the fan can be screwed down onto the brackets. Also mark the outline of the where the fan blade travels over the brackets. This piece of metal needs to be removed. Once you have marked the holes and cutout area, remove the fan and the brackets. You can use an angle grinder to carefully remove the unwanted metal from the cutout area.

Once your brackets are complete, insert the 40mm long fan mounting screws so that the heads are on the underside of the bracket and remount the brackets. Depending on the exact model of your fan, you may need to insert some spacers between the fan and the brackets. The aim is to get the magnets as close as possible to the bottom of the case (this will be the top when in use). The spacers can be additional nuts or pieces of plastic tubing.

Its now time to mount the magnets on the fan as they should be bonded together by now. Again I used liquid nails to fix the magnet to the fan. The hardest part is getting the magnet in the exact centre of the fan. Put the magnet where you think it is in the centre, then spin it hard and if you can feel any vibration, shift it and try again. If you have any vibration, you will really notice it when you are using the stirrer.

Once the fan has been mounted, we can now wire the stirrer up. Connect one wire from the fan to the earth (negative) point on the power socket. Connect the positive point on the power socket to the centre point on the pot. The other lead from the fan connects to one of the outer points on the pot. It is hard to tell which one to connect to, but looking at the back of the pot, with all the lugs pointing up, use the one of the right.

If you have used the case that was listed above, then you will have a length of round plastic. This fits into the slot in the case lid (which will become our base) to make a waterproof seal. It may be longer that what you need and may need to be trimmed. The feet can also be fitted to the lid now as well.

The case can now be assembled. Once it is assembled, place one of the stir bars on top of the case and it should align itself with the magnet on the fan. Its now time to try it out!

Using the stirrer
Put the stir bar on top of the magnetic stirrer and let it align with the magnet on the fan. Start the stirrer, turn the pot to the fastest setting, then adjust the speed downwards until you reach the required stir rate. Depending on how the pot was wired, this may be fully clockwise or fully anti-clockwise.

When using the stirrer you need flat bottom vessels like Erlenmeyer flasks. In the 100mL flasks, use the 50mm bars and in the 1 or 2 litres ones, use the 70mm bars. You may also find other contains like ice cream topping bottles that have flat bottoms.

I usually pitch the started into 100mL of wort, stir it for 1½ to 2 hours, let it settle for an hour or two, then step the starter up to 2 litres and stir again for 1½ to 2 hours. Leave the starter overnight and you should have an excellent started the next day.

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#2 DocOc



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Posted 17 April 2006 - 07:47 PM

University surplus auctions are a great place too. You can pick one up for like 10-15 and often it's a heat plate too.

#3 Hippie3



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Posted 17 April 2006 - 07:58 PM

Magnetic stirrer construction
This article is based on my original posting to the Homebrew Digest, from HBD #2570, Nov 29, 1997. Wow was it really that long ago!
So here is it several years later. I made some comments about my starter procedure and stirrer in a recent post to the Homebrew Digest and received several inquires. I decided it was time to update the original article.
Pretty much, the basic idea hasn't changed. Attach a magnet to a motor, build a base, find a suitable vessel, add liquid and one stir bar. I built a second stirrer and have included pictures of both at the end of the article.
It is somewhat difficult to provide a step-by-step guide to building a stirrer. The two biggest variables are choice of building materials and the dimensions of the motor. There are also many methods of attaching the magnet to the motor. Your choice of motor, magnet and magnet mounting will determine the construction techniques and the end results as well.
The base of the stirrer can be constructed from practically anything. Wood, plastic, metal (aluminum is best) or anything else you can dream up. The main consideration is that the base is strong enough to support the weight of your starter. Also the base should be large enough so as to provide good stability. Making a 2" x 2" base and then using an erlenmeyer flask with a 6" diameter base is asking for trouble. Various containers can also be used with excellent results.
There are two basic types of motors, AC or DC, which could be used on this type of project. DC motors are probably the best choice because availability. Also DC motors tend to use voltages that commonly range 3-24 volts. This voltage is low enough so that if you have an accident and get everything wet there will not be and electrocution hazard. Speed control is probably easier, IMO, with DC motors than AC motors as well. I will discuss power supplies and speed control later. I have found that a good motor is a muffin type fan. These fans are usually have a nice flat surface to which you can epoxy a magnet.
There are too many choices of magnets to cover them all. You should be able to locate magnets on most any scientific, parts or electronic retail web site. Radio Shack carries magnets that should work (I have not tried them). The main goal is to have the magnet be strong enough so that is maintains it's coupling to the stir bar. Almost any flat magnet will probably work. Try and avoid round/rod type magnets, as mounting them to the motor is probably a little more complicated. Rare earth and ceramic magnets are the strongest magnets, but they are usually higher priced as well. Try and avoid overly large magnets. Obviously, larger magnets weight more and if you have a small lightweight motor there may be too much stress on to motor.
Stir bars:
You can buy them from one of the science supply places or you can make your own. To make your own stir bars, simply cut the head off a nail and then cut it to the desired length. Then put this into a piece of plastic tubing and seal the ends shut by melting them and pinching them closed. 20p nails and 1/4" OD tubing is a very good combination. I used Teflon tubing but nylon should work just as well. I used the burner on my gas range for a flame to melt the tubing. A lighter should work too. Be careful not to catch the tubing on fire. Commercial stir bars are coated magnets is it will probably be easier to obtain good magnetic coupling with a commercial stir bar. But what the heck, who can complain if it's free. A stir bar length between 1/2" to 1" should be sufficient in most applications. The key is matching the stir bar length to the magnet. For example, if the magnet is 1" then the stir bar should be close to 1" for best results. I used my homemade stir bars for years before a friend gave me a couple commercial stir bars from the laboratory where he worked.
Putting it all together:
After you construct or obtain the base, you will mount the motor and magnet. The important thing to remember is that the magnet must be in close proximity to the stir bar to maintain coupling. It will probably be necessary to include some way to adjust the magnet/motor height up/down. The base on my current stirrer is 1/2" plywood (that's what I had on hand at the time). A hole is drilled in the center of the base for the magnet. I mounted my motor on a piece of flat aluminum. The height of the magnet in relation to the jug I use is adjusted by using various length spacers. My starter container is a 4L wine jug. Most jug type containers have a concave bottom. The magnet actually protrudes thru the base. A flat bottom container such and an erlenmeyer flask will not work on my stirrer unless I adjust the height of the motor mount bracket so that the magnet is flush or slightly below the surface of the base.
There are also more that 101 ways to attach the magnet to the motor. If you use a muffin type fan you should be able to attach the magnet with some epoxy. If your motor has a large enough shaft you may be able to epoxy the magnet to it. It will probably be more common that the shaft diameter is too thin to mount a magnet, in which case some sort of coupler will need to be used. This may be as simple as drilling a hole in a piece of material that is the same size as the motor shaft and then using epoxy or super glue to hold them together. The main consideration when mounting the magnet is that the magnet be fairly balanced as it turns. Is does not have to be balanced to the n-th degree. If the stirrer/motor is vibrating and moving all over when the motor is running at a fast speed then it is probably safe to say that the magnet is not balanced. In both of the stirrers I built, I found the simply centering the magnet was sufficient.
Power supply and speed control:
This is it, the final step. So you've got everything built and assembled, now just hook up the juice and let it rip. Most DC motors require anywhere from 1.5 - 24 VDC. Motors that require more than 12 volts were probably special purpose motors. If you have one, then you probably have the correct power supply too. Most DC motors that you will find are probably 3-12 volts. The easiest way to control the speed of a DC motor is to adjust the voltage. There are two basic options. One is to find a fixed voltage supply that provides the desired speed. This is very easy. Radio Shack sells a range of "wall cube" AD-DC adapters. One of them should provide a speed that is acceptable. The disadvantage is that you will not be able to vary the speed. Another option is to use an AC-DC adapter that provides 12-18 volts and add an adjustable circuit. The circuit is based on the LM-317 voltage regulator and requires only two resistors (one fixed and one variable). See additional power supply construction notes. I have found that I typically run my stirrer at one speed. Occasionally I will increase the speed. It is usually on brew day when I add the final energizer boost. I do this because the yeast that settles out usually is pretty thick and pasty and revving the stirrer helps get the yeast mixed. In a laboratory setting the stirrer will be used with various containers, volumes, liquids and stir bars. Because of this speed variability is more important.
UPDATE: Radio Shack sells a multi-voltage "wall cube" power supply; catalog number 273-1667. The voltages are 3, 4.5, 6, 7.5, 9 and 12v. While this is not a true variable supply, the range of voltages should provide the desired speed control. The current rating is 800mA, this should be sufficient for most small DC motors. I have not tested this product to determine if this is the case.
My original stirrer:
Photo 1 This picture shows the magnet on the muffin fan. The fan body is metal and the magnet "stuck" to the fan without problem. If you have a plastic fan you would need to used epoxy or silicon adhesive. The wires are for the DC power connection.
Photo 2 This picture shows the wooden base. Notice how the magnet is slightly below the surface. This distance is the distance that needs to be adjustable to ensure proper magnetic coupling. If the distance is too large, the stir bar will not rotate with the magnet. If the distance is too close, the stir bar will tend to drag.
Photo 3 This picture shows the stirrer, erlenmeyer flask and stir bar. Notice that the stir bar length is roughly the same length as the magnet. This is on of my homemade stir bars.

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#4 Hippie3



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Posted 17 April 2006 - 08:01 PM

My latest stirrer:
Photo 1 This is the base. It is larger than my original because I am using a larger container. I also added the edges to provide additional stability. The edges also insure that the container is centered over the magnet. The knob is the speed control.
Photo 2 This is a close-up of the base. Notice that on this stirrer the magnet extends past the surface of the base. This is because my current container, a wine jug, has a concave base. The rubber pad is a nice non-skid surface. They also help adjust the height/coupling of the magnet.
Photo 3 This is the underside of the stirrer. The motor is in the center. The height of the magnet is adjusted by using different heights legs in each corner of the bracket. The variable power chip, LM-317, is on the right. The top is the variable resistor for the speed control. The bottom is a plug for connecting the AC-DC wall cube converter.
Photo 4 A close-up picture of the LM-317 chip. The chip tab is soldered to the circuit board for easier mounting. It also provides a heat sink, however, the chip barely even gets warm when running the motor. The circuit could be built entirely on a circuit board. I used "ugly" construction because the circuit is very simple.
Photo 5 A close-up of the motor, magnet and mounting bracket. This shows the legs of the bracket. The shaft of the motor is 1/8" and I needed to use a shaft coupler. The coupler is aluminum. I put the magnet in a cap and used RTV to attach the cap to the coupler.

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#5 shimmy



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Posted 17 April 2006 - 08:12 PM

very cool hip thanks for saving me some money:headbang:

#6 BuckarooBanzai


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Posted 17 April 2006 - 08:36 PM

Very cool post. DIY knows no bounds, eh? Somebody tell Bluehelix...he would LOVE this...

#7 Guest_pcsillypj_*

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Posted 17 April 2006 - 09:04 PM

this is some great stuff hip...thx for posting it....

#8 arezap


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Posted 17 April 2006 - 11:17 PM

Now I'll build one for my LC's seeing what it takes to make one.

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Posted 18 April 2006 - 12:56 AM

:bow: thank you :bow:

#10 cordyceps



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Posted 18 April 2006 - 01:17 AM

Freaking great post! I'm gonna build one this weekend. :dance:

#11 hogwild



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Posted 18 April 2006 - 01:28 AM

This will definately help with many things. I might make a couple to constantly stir LC's.

#12 Hippie3



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Posted 18 April 2006 - 07:31 PM

Freaking great post! I'm gonna build one this weekend. :dance:

anyone who builds one-
plz photo-document the process
and share with us any feedback.

#13 Hippie3



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Posted 26 April 2006 - 08:04 AM

Stir Bars-

Used small bore rubber tubing, nails with head cut off & RTV high temp silicone. Cut head off nail, insert in tubing & silicone seal ends

old organic chem trick... a paper clip with the inner loop bent out from the larger loop at a 45 degree angle works great as a stir bar in water or other solutions of a low viscosity, just make sure theres nothing too chunky in there, but it would chop up myc pretty well.

make stir bars from the sheathing made for bicycle brake cable.
it already has a steal coil inside the plastic coating. its 1/8" thick and is flexible.
cut it a little short of the the with of the jar and dip both ends in this stuff

tubing source

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#14 Hippie3



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Posted 06 May 2006 - 07:14 PM

another design-
posted by calavera

just completed my stirrer, and its so simple, and so cheap that i think you should try it!


1 big computer fan with speed control

4 screws that fits in the fan's four hole

2 magnetic stirrer sticks (original)

1 cd case

1 12v power supply for the fan

1 little piece of bluetech

stick one of your magnetic sticks on the center of the fan.
screw in the 4 scews.
the smaller part of the cd case goes on the top of the screws,
adjust the screws until the cover is as close as possible,
but not touching the case.
plug in, adjust the speed have fun!
bluetech is like a sticky plasticine.
they use it to stic posters on the wall and etc...
its just a quick way to stic your magnet on the fan.
you need something like this
since theese magnets are covered with a special plastic thats not good for gluing.
the rpm is what you decide
(i adjust it just to see a little vortex on the top),
you can go down to very slow and the max will be the fans max,
it's like 1500rpm.

there is one little problem,
if you adjust your fan to run slow, and there is a power loss,
the fan wont start again, and you need to help it to start by knocking it a little.
i am trying to figure that problem out
my one is running since 24 hours,
but even now i can clearly see mycellial growth
(i injected a small amount, around 0.5ml of mycelia)

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#15 Hippie3



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Posted 07 May 2006 - 06:30 PM

stir bar

Cut this [hot glue stix] to your preferred size.
Cut off the head and push this inside
Then just melt where you stuck it in.

another idea-

did find some heat shrink tubing lying around, shrunk it around a 1" length of solid wire. The metal no longer clanks (gently) against the bottom of the jar while spinning which means two things; less noise and more spin. My vortex hits full-throttle more reliably with the tubing.

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#16 Hippie3



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Posted 07 May 2006 - 06:42 PM

by splifner180

I made myself a working magnetic stirrer using only stuff I had kicking around the room. The only "exotic" thing used was a spare GO [the game] stone "bowl" (though it's square-shaped). The whole thing from start-to-finish was roughly 30-40 minutes.
Obtaining the magnets are only a problem if you aren't someone who has spare hard drives kicking around as a matter of principle.
Ok, so here it is. The parts all in one spot:
There you can see the enclosure (GO stone box), some arbitrary-length garden ties (use string if you want, doesn't matter), the computer fan with the magnet already attached, superglue (not shown), some washers (to stand off the fan from the work surface) and a 12v power supply pinched from a humungous box I have stuffed with such things.
The assembly was simple.
* Match fan up to lid. Use sharpie to mark four holes. Drill holes.
* Strip wires on both the fan and the power supply. Attach. If the fan spins in the "wrong direction" you have the wires hooked up backward but I don't think it'll harm anything if you do.
* Attach HD magnet to the fan. It should stick since it's an extremely powerful magnet and the fan has metal inside. Power up fan.
* The goal at this point is to find the "sweet spot" for the magnet, the placement that will cause the least wobble in the assembly. A millimeter can mean the difference between a kitten purr and the magnet being flung from the fan so make small adjustments.
* Once you find the sweet spot, superglue that mofo down. I didn't bother with the jar lid like blacklabrat did.
* With the fan pointed "up" (the magnet facing up), take one wiretie end and thread it through the fan holes from bottom to top. Take the other end of the wiretie and thread it through a parallel hole in the fan. The wire tie should look like the rope on a swing set and the fan/magnet should be the wood swing itself. The wire tie cradles the fan.
* Thread enough nuts unto the wire tie so that the spinning fan will not hit the lid when pressed against. Sorry no pics for this -- my camera batteries died. Here's a drawing.
* Do the same through the other two holes. Now you'll have four wires cradling the fan with washers dropped over the wire to act as a standoff.
* Place the cover over the fan, threading the wires through the holes you drilled. Twist the ties together to secure the fan assembly to the lid.
* Place the lid over the box. Make a notch for the power wires if you want. I didn't.
That's it. All done. Here is the stirrer in action.
I should have taken multiple pictures. That one does it no justice. There is a righteous vortex in the container right now. The one in the picture is pretty small.
I should mention that there are TONS of ways I could have done this differently. I justed wanted to do it with the items I had on-hand and ...well ...these are the items I had on-hand. It's whisper quiet (calibrating the magnet is critical) and it's been running now for about 80 minutes without so much as a peep.
The stirring rod itself, like the other thread mentions, is just a 1" piece of ferrous (magnetic) metal. I just snipped a bit off a spool of ground wire I had kicking around. Heck, even a small nail might work perfectly. Tomorrow I'll pick up a bit of shrinkwrap to place around the rod. I tried different sizes (I think 1" is optimal) and I tried doing multiple bits of metal (it worked terrible for me, they all clumped together). Tomorrow I'll probably try to attach two bits of metal to polar ends of something non-magnetic, seal with shrink-wrap and see how that works. Who knows?
I also have a short video I took.
t was absurd how easy it was to make. Granted, I have things in my room that probably 85% of the forum members DON'T but none of the items are too exotic. The worst is probably the hard drive magnet and all you have to do is hit up a local computer replair place and tell them you'd like their dead drives to pull the magnets out of.
If anyone asks why, just tell them the magents make good clamps because they're so bloody strong.
I think tomorrow I'm going to pick up a thin piece of lucite (to make a proper lid), some extra long screws and some nuts. Hell, I can probably even throw a noise-dampener in there for haha's.
last note-
to reduce motor resistance i cut all the fan blades off using a pair of wire dykes

day 2
day 3

#17 Hippie3



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Posted 07 May 2006 - 06:59 PM

by blacklabrat

I would like to introduce my new little friend...........



OK, Right off the bat let me make it clear that I can take no credit for this. It is an idea that has been ripped off and inspired by several others who have done the DYI magnetic stirrer plate method. It works great, took me less than an hour to make and the best didn't cost me a dime. FREE! Just scraped up a few items I had laying around the house.

Here's how it was done:



~ Started off by mounting the fan to a block of scrap lumber. Connected the fan to the transformer. Originally I was going to add a dimmer switch, but after testing I deemed it unnecessary.

~ Next, I took a canning lid and hot glue gunned it to the top of the fan. Place the magnet in the center of the canning jar lid. Tested placement by plugging unit on to make sure there was no wobble. Hot glue gunned it once the magnet was properly centered.


~Then I cut two blocks of lumber about 1/8" taller than the height of the fan/jar lid/magnet assembly. Mounted these to the side of the fan with glue and screws. Fixed a square of plexiglass to the blocks. This is the base surface where the LC jars sit.

Turned on to make sure that the fan was spinning freely.

Check. Everything is running quiet and smooth

Now I need some stir rods................Hmmm. Ebay? Nah. Screw buying them!
I was now determined not to shell out any cash for this project. After playing around with several ideas, many which were too loud, slow or would require me spending some of my precious beer money .....

I was reminded how sometimes the simplest solutions are the most effective.


A small piece of wire about 1/4" long is quiet, effective and best of all CHEAP!

I tested it by placing a small piece of toilet paper in the jar w/ H2O and with in an hour it had broker it into small fibers.

Yeah yeah. I can hear it now."Isn't the wire going to rust?"

Eventually. But not before the LC is done. They are essentially disposable, costing you about 10 cents per 100!

And there you have it.

How well does it work? Check out the first pic!

It spins like Dorthy in a tornado.

I first attached the canning lid to the fan blade with super glue, making sure that it was absolutely centered. I then played around with the placement of the magnet making sure that it spun with out wobbling. As soon as I had the placement correct I outlined the magnet w/ a sharpie, and secured with glue.

Its not really necessary, just the way I happened to do it


Need to warm up the temp of your LC? Try this:

Made one minor improvement to the Sir Mix-A-Lot magnetic stirrer.

I usually do my LC in temps around the high 80s. Currently temps in my neck of the woods are about 20 degrees too cold & I'd rather not put the stir plate in the incubator, so........................


My solution:

I removed the plexiglass base plate and temporally replaced it with a 4 quart lexan tub. The tub is outfitted with a aquarium heater set to 87 degrees and a thermometer. (I realize that the heater is a little too large for this particular application..going to get a smaller one this weekend)
I can now dial in to the exact temp I need.

a piece of wire shrink wrap (can get it in small quantities at a hardware store or rat shack) will seal up that piece of wire nicely... slip it in, flame it up, watch it melt over the wire... voila, rust free low cost stir bar....

....doesn't have to be a cell charger, any "wall wort" a/c adapter whose voltage matches your fan (almost always 12 volts) will work. if you don't have one, universal ones are cheap, and sometimes have a switch to adjust voltage. (less than 12v = fan will still spin, but slower = a variable speed control version!) cut off tip, strip wires, twist together with wires from the fan. its ok to be off by a little, eg a 11.5v or 12.4v or such adapter is gonna do just fine with a 12v fan. don't go beyond 12.5v or so or risk burning out the fan, and anything much less than 11v is gonna result in a slow spinning fan. if it doesnt spin or spins backwords, match the wires up the other way around. radio shack also has 120vac fans that will work on current straight from the wall: in which case get a cheapo extension cord, cut off female end, strip and twist up wires in similar fashion. (use of wire nuts and/or lots of electrical tape is a good idea, 120vac can be dangerous if your wires are exposed! the voltage from a DC adapter like a cell charger will NOT harm you, but if the wires touch eachother you end up with a dead adapter)... if wiring the AC variety without an adapter you can't get the wires "backwards" as it will work either way.

#18 dirtyman



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Posted 08 May 2006 - 02:37 AM

A buddy and I tried to wire one up this week. An old computer fan was glued to some wood with a 1/2 pint lid centered and glued on top of the fan, strong magnets (radioshack cheapies don't work, friend found 2 small yet powerful ones inside an old CD player by the laser) centered and glued on top of the lid. Trying to adjust the speed was a bitch, we're still trying to figure that out by experimenting with a couple resistors. Gonna buy a small stainless steel nail for the stirrer inside the jar. I should be done sometime this week and will try to take pictures.

Anyone know where to get some good magnets for cheap? I'm thinking that you need a good grip on the stir bar inside the jar to make it work.

PS: I like the Agar-like typing of that 1st guy hippie quoted above me :p

#19 jestah



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Posted 09 May 2006 - 07:22 AM

After reading this thread (thanks hippie for putting it all together) I was keen to put one together so I did.

I used the basic ideas from the first post but changed the flowing:

I found an old computer on the side of the street and stole the hard drive and a fan. From the HD I took the THIN but STRONG magnets and spent the next hour getting them balanced on the fan. Set it up so you can turn the fan on and off while testing the balance of the magnet. It’s well worth the effort IMHO. Then super glue them in place. I just ran a bead around the edges of the magnets.

Once this had set up I used silicon (same as I used for my airports) to stick the fan to the lid of the case. I used thin coins as stand offs so there is a thin layer of silicon on each corner where the screw should be. I like this as it acts as a bit of a buffer for the small hum my fan has. Wire in the pot and power and wahay one dam fine stirrer. It hold a 1L flask for yeast starters but will also do concaved jars for LC and the like (that y you need the STRONG magnets)

I think spend the money and get a decent water tight box... not only is it a bit safer if you have a spill but it looks so spliffyly good

I will try to get some photos up tomorrow or the next day. Should i make my first tek???


#20 Killjoy



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Posted 10 May 2006 - 05:36 PM

Just finished A DIY stir Plate. Found an Amazingly perfect fan at the Thrift store. (actually 2) $2 for 2 ceramic magnets at Homedepot or A craft store. A dimmer switch spliced into an extention cord and a little super glue.
Only mod to the fans was to cut the gaurd off/level so a piece of old plexi would sit on it.

Total cost about $11 for the 2 of them.

missed the Nail/tubbing idea for a stir bar and tried coating some smaller ceramic magnets ($2 for 8 at same places) in liquid rubber.
Worked great until I ran it over night and came back to a dark Cloudy LC and shreiked about contams, then realized the rubber had rubbed off and the "cloudyness" was tinny bits of the corners of the magnet. Think I'll try tubbing on them and be set!.

Thanks for info to make this idea work!

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