My Stirplate... Cheap and Easy Build...

[Coppinburgh]

Just finished mine up today! Great thread! It made the job super easy with the very little electrical knowledge I have! Thanks!


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[Gregthespy]

so, collecting parts for my stir plate while I fabricate my housing and need to know, one hard drive magnet or 2 button magnets? Happen to have both, in my mind a single one would be easier to center but the dual button may create a better polarity difference. I've got a variety of stir bars on the way in the mail so I should be set with different options. What's the general consensus?


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[Coppinburgh]

View attachment 190162 so, collecting parts for my stir plate while I fabricate my housing and need to know, one hard drive magnet or 2 button magnets? Happen to have both, in my mind a single one would be easier to center but the dual button may create a better polarity difference. I've got a variety of stir bars on the way in the mail so I should be set with different options. What's the general consensus?


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I recently asked the same question in a different thread. One hard drive magnet seemed to be the most frequent answer I got. It worked well for me.


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[Gregthespy]

So many threads with so many posts, the search doesn't seem to narrow things down much! I appreciate the quick feedback. I'm not partial to either, just whatever's easiest and does the job.


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[Cposten]

Just finished mine up today! Great thread! It made the job super easy with the very little electrical knowledge I have! Thanks!View attachment 189445


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That is freakin awesome man.

 

[MaxStout]

View attachment 190162 so, collecting parts for my stir plate while I fabricate my housing and need to know, one hard drive magnet or 2 button magnets? Happen to have both, in my mind a single one would be easier to center but the dual button may create a better polarity difference. I've got a variety of stir bars on the way in the mail so I should be set with different options. What's the general consensus?


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I use 2 button magnets, but many people have good luck with the HD magnet. I think the success depends on the length of the stir bar compared to the distance between poles of the magnet. If you use a hard drive magnet, you will need to select a stir bar that is comparable in length to that. OTOH, with button magnets, you can pick the stir bar you want, then position the button magnets to match it.

 

[Randy64]

Thank you OP for including Radio Shack part numbers. We couldn't find the bin for the one of the parts and we used the part number to track one to the back room.


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[TsunamiBeer]

Just built one myself. Thanks so much. Awesome easy project.

 

[bannerj]

Thrown bar over and over and over again....help.

Did all of this to spec. Using one HD magnet, a 2 inch stir bar, a 12v fan and a 7.5v power supply. I have the magnet very close to the bottom of the flask. It's all in a cigar box.

The potentiometer can't turn on at a low speed. I have to turn it up over half way to get the fan to move. Then I can slow it down to a lower speed. Otherwise it kinda rocks in idle.

help

 

[MaxStout]

Thrown bar over and over and over again....help.

Did all of this to spec. Using one HD magnet, a 2 inch stir bar, a 12v fan and a 7.5v power supply. I have the magnet very close to the bottom of the flask. It's all in a cigar box.

The potentiometer can't turn on at a low speed. I have to turn it up over half way to get the fan to move. Then I can slow it down to a lower speed. Otherwise it kinda rocks in idle.

help

Since you can't change the distance between the poles of the HD magnet, you might need to try a few stir bars of different lengths. Go on Amazon--they sell every size you can imagine.

The other solution would be to remove the HD magnet, get two rare earth "button" magnets and place them at the right distance from one another on the fan in order to keep the stir bar in place. It takes a little experimentation to get it right.

BTW, I have the same issue with my potentiometer. The motor won't start turning until the input voltage reaches a certain point. From that point upward, the speed control works fine.

 

[bannerj]

Since you can't change the distance between the poles of the HD magnet, you might need to try a few stir bars of different lengths. Go on Amazon--they sell every size you can imagine.

The other solution would be to remove the HD magnet, get two rare earth "button" magnets and place them at the right distance from one another on the fan in order to keep the stir bar in place. It takes a little experimentation to get it right.

BTW, I have the same issue with my potentiometer. The motor won't start turning until the input voltage reaches a certain point. From that point upward, the speed control works fine.

I have the two magnets from the HD. Should I go with the large washer and try to space the magnets further apart?

 

[MaxStout]

I have the two magnets from the HD. Should I go with the large washer and try to space the magnets further apart?

OK, my bad. I assumed that your HD magnet was one piece.

Yes, you could experiment with placement of the 2 magnets. It's kind of a hit-and-miss process. Try to set them such that they don't cause the fan to go out of balance (place same distance from center and 180 degrees separated in the circle).

 

[bannerj]

I pulled two magnets but have just been using one. I'll try to space out two. Thanks

 

[misterbk]

The potentiometer can't turn on at a low speed. I have to turn it up over half way to get the fan to move. Then I can slow it down to a lower speed. Otherwise it kinda rocks in idle.
help

You're using the design where the potentiometer connects directly to the fan, right? That's just a limitation of that kind of circuit. That behavior is solved by a PWM circuit, but building one is much more complicated than putting a pot in series with the fan leads.

So, don't worry, I'm sure the circuit is built fine. That's just how that kind of circuit behaves.

 

[drwoods21]

I just finished my build of this. Works great! I did realize that I have to use a small stir bar to make sure it doesn't spin off. Doesn't help that I am using a 1 gallon jug as the container, doesn't have a completely flat bottom like a flask does. Seems to work fine though as long as I keep the speed down.

 

[bannerj]

You're using the design where the potentiometer connects directly to the fan, right? That's just a limitation of that kind of circuit. That behavior is solved by a PWM circuit, but building one is much more complicated than putting a pot in series with the fan leads.

So, don't worry, I'm sure the circuit is built fine. That's just how that kind of circuit behaves.

I've done minimal mods with circuit boards in microphones. Can a pwm circuit like you say be made on the cheap?

 

[misterbk]

I've done minimal mods with circuit boards in microphones. Can a pwm circuit like you say be made on the cheap?

Absolutely. There are lots of ways to build it. The last one I built used:

• 74221 'dual monostable multivibrator' ($0.62)
• Three capacitors ($0.15 each, TOPS)
• Six or so resistors ($0.02 each)
• Potentiometer (About $0.70)
• Transistor (Anywhere from $0.05 to $1.50 depending how beefy)
• Wire (Free, if you already have some.)
• PCB (About $2.00)
• Potentiometer Knob (Maybe $2.00. Or make one out of wood.)
• (Assuming you already have enclosure, flask, fan, magnet, stir bar etc.)

The trick will be building it with stuff that you can find locally, because shipping $6 worth of parts probably costs another $6.

It's highly likely there are modules you can buy that do it for you, or easier / better ways than using the 74221. (In fact I'm almost certain there's an easier part, I just already knew how to use the 74221.)

The 74221 essentially plays 'ping-pong' with itself. When you turn on the power, side A triggers as soon as the reset signal turns off, and stays on for a duration specified by pins 1 and 2 of the potentiometer. When it turns off, that triggers side B to turn on for a duration specified by pins 2 and 3 of the potentiometer. When side B turns off, it triggers side A, repeat until you power it off. So turning the potentiometer clockwise makes side A stay on longer, and side B stay on shorter. When you listen to the output on side A, you get a PWM signal, so you send that signal to your transistor.

Here's the one I built. Describing it makes it sound more complicated than it is in real life.

I used 3-pin fan headers to connect the board to the motor it was driving, for portability. (It was driving a high-powered screwdriver motor for hours at a time, hence the heatsink, which actually turned out to be unnecessary.) The connector on the top left is where the potentiometer plugged in. The one on the right is where the power plugged in. There's another behind the heatsink where you can't see it, where the motor plugged in.

Interesting side note: 4-pin fans have a built-in transistor for use with a PWM signal. That's how the computer controls the fan speed. It has some specific requirements though, like a 25mhz frequency on the PWM signal, which could make things tricky with off-the-shelf stuff.

 

[Beernik]

I've got mine going for the first time. Freaking rocks!

WLP 300 has chewed through a 1L, 1.057 starter in 24 hours.

 

[WSJ]

Finished mine today. I'll add a green LED and a POT to it later.
Yeast test will be done in few days re revive the yeast that arrived today.
I need it in few days for my next brew and one bottle is not enough.

 

[Seamonkey]

Yes! I just finished my build according to your wiring diagram, Mellow52! Thank you for not cutting corners, I hope this will last awhile! Should be easy to replace the fan if it ever goes out!

 

[Powhatan]

Success! Thanks HBT for the info and guidance.

 

[barnaclebob]

Just built mine. Used a 5V power source with a 12v fan. Its a bit underpowered but still creates a nice dimple so it should be fine.

 

[Peruvian802]

So after 3 trips to Radio Shack I'm still stumped by which potentiometer I need. I tried the 25ohm and then a 500k ohm rheostat but neither would slow down my fan enough for use. Does anyone have any suggestions?

Here's my fan, if that helps.

 

[Newsman]

So after 3 trips to Radio Shack I'm still stumped by which potentiometer I need. I tried the 25ohm and then a 500k ohm rheostat but neither would slow down my fan enough for use. Does anyone have any suggestions?

Here's my fan, if that helps.

Looks like that's an A/C (Alternating Current.) You want a DC (Direct Current) fan. There's the problem.

 

[Peruvian802]

Screw Thomas Edison!

 

[Brettomomyces]

Save yourself a lot of effort and buy a fan which comes with the speed control potentiometer already:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835200027

With code SUPSALE033, it's $5 shipped. It's a very easy build.

So if I went with one of these, you just need a knob, switch, and power supply?

and a magnet, duh

 

[Jsamp]

I just got this build out today. I have less than $20 in it and was surprisingly easy to build. I ordered a stir bar and flask the other day and havent received it yet. The only way I could test it was to use a screw that didn't have a real strong grip on the magnet. On the stir plate itself it span real well. In a glass with about 1/2" thick bottom it had a slow spin. I figure with a magnetic stir bar and a flask that isnt as thick it should spin like a champ. Thanks for the guide.

 

[barnaclebob]

So after 3 trips to Radio Shack I'm still stumped by which potentiometer I need. I tried the 25ohm and then a 500k ohm rheostat but neither would slow down my fan enough for use. Does anyone have any suggestions?

Here's my fan, if that helps.

View attachment 217813

If your rheostat does control the speed, just not enough you could try adding things to the fins to increase air resistance...

 

[barnaclebob]

You know it would actually be better to use one of these for speed control, the cost isnt much more, they come in various voltages:

http://www.amazon.com/dp/B009HKFAIQ/?tag=skimlinks_replacement-20

 

[Jsamp]

I got my flask and stir bar in the mail today. As I suspected the stir plate does indeed work great. Thanks again for the build.