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Old 05-16-2009, 07:46 AM   #1
j_jones84
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Default DIY stirplate FAN SPEED

How do I slow this mother down?

Bought a DIY style plate off of ebay to save myself from learning basic electronics. Well... ****. It doesn't work. Keeps throwing the bar. I believe I could fix the problem by slowing down the fan because the slowest speed on the dial is too fast. Not sure how he made it but the dial travels about 80% before the fan even kicks on. Here are the specs in the ebay ad, any thoughts?

These custom built stir plates are made with all new components. They are assembled using Neodymium magnets, a 12 vdc power supply and a brand new 80 mm computer fan. It has a variable speed control and a separate on/off switch on these units. All components are soldered for the best performance and reliability. I will also include a 1" x 1/4" stir bar or 1 1/8" x 1/4" stir bar!

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Old 05-16-2009, 08:37 AM   #2
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Variable speed control my ass. There is one speed.. FAST.

There is no circuit board like I see in some of the pictures. Just the knob, on off switch, and some wires.

If I need to add a resistor, how do I do that?

Right now I have my flask gently tipped up with a pencil and the side with the bar on the center of the fan and it is just hopping around. Is that good enough to keep the yeast in suspension?

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Old 05-16-2009, 10:44 AM   #3
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Well, I'm not sure which one you have, but a couple of thoughts..

  • Use a smaller power supply.
  • I use a potentionmeter (variable resistor), part #271-215 at radio shack to adjust the speed (power) going to the fan.

You "could" add a resistor, but it would be difficult to guesstimate which size you need. Here is a how the wires are hooked up on mine:

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Old 05-16-2009, 11:17 AM   #4
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Add a second pentomenter (also called a rheostat I think) to it. Or you may be able to replace the orginal one.

Here is another thought. Your magnets may not be polarized correctly. Take your stir bar and slowly slide it accross the top of your stir plate where the magnet is on the fan. Don't let the fan move and keep the stir bar in the same direction. Do this for about 20 strokes. Then put it in your flask and give it a whirl.

I had a bar that kept getting thrown, and it was due to the polarity issue.

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Old 05-16-2009, 04:25 PM   #5
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I will try the polarity thing but due to the tornado touching down all the time I think it is more speed related. How would I go about adding a second pentomenter? how would the two dials work together?

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Old 06-04-2009, 02:41 AM   #6
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Ok guys I'm working on my stirplate. I haven't added the potentiometer yet but I can't get my stir bar to spin at all. It wiggles a bit and then like dances away. I am HOPING that slowing the beast down will fix it? I am using 12V power supply and a 12V GPU fan. I got a project enclosure and a potentiometer and I'm gonna try to wire it like this. We'll see! I'll post results soon. If I fail at this I'll post a video so you guys can help me out! I started with rare earth magnets from harbor freight (they were tiny) and now I've switched to hard drive magnets, but they seem quite thin and not as hefty as some photos I've seen.

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Old 06-04-2009, 02:45 AM   #7
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12 volts to a 12 volt fan will want to run at normal fan speed.
One suggestion - find a wall wart you're not using that has an output of 6, 7.5 or 9 V and try that... The variable resistor (potentiometer, rheostat) will be able to do a better job.

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Old 06-04-2009, 02:53 AM   #8
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Quote:
Originally Posted by Hang Glider View Post
12 volts to a 12 volt fan will want to run at normal fan speed.
One suggestion - find a wall wart you're not using that has an output of 6, 7.5 or 9 V and try that... The variable resistor (potentiometer, rheostat) will be able to do a better job.
ok I have one of those. What is the "symptom" of too fast fan? Does it look like the stir bar ain't doing much? I get basically no activity except the stir bar floats to the outer portion of the flask unless I hand spin the fan and then i can get the stir bar to spin a wee bit. I'll try potentiometer and lower voltage and if still no dice I'll post video.
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Old 06-04-2009, 04:21 AM   #9
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Ok. I wired my potentiometer based on the diagram above and now the switch works, but it only turns it on/off. I have to turn it to max and then the fan turns on. This is true with both 12V and 6V adapters, which I thought was weird. Any suggestions? I can send a pic but it looks like the one above, I just didn't solder it yet. What happens is if i turn the fan off and on a lot, trying to keep lower speed, the stir bar starts to spin up, but then it gets thrown either from too much speed or from the fan turning off.

By the way, this is the fan I am using, it has red/white/black wires. I'm not sure what the white wire is for because red is power.

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Old 06-04-2009, 04:33 AM   #10
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FWIW, here's mine, pretty much as simple as it gets. I've found that ~4.5v works well for 1-2L, and ~5v works for 2-2.5L. Just used old cell phone chargers, an old computer fan, and some salvaged rare earth magnets. $8 and I got 2 stirplates (costs for bottle and stirbar)



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