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Old 11-01-2011, 11:25 PM   #1
blawjr
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Default DIY stir plate keeps throwing stir bar.

My fan spins too fast so it throws the bar, in order to simplify things I'd like to skip adding in a fan speed dial. I'm using a 9 volt fan with a 9 volt power supply, question is, can I use a lower voltage power supply, say 4 or 5 volts and it still work? Will it then spin at half the speed and not throw the bar?

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Old 11-01-2011, 11:49 PM   #2
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I believe most fans have a minimal voltage required to get it spinning and I'm not sure if 4-5V will cut the mustard. Are you able to adjust the distance of the fan from the stir plate surface? I lowered my fan away from the stir plate because it would throw the bar when I first turned it on.

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Old 11-02-2011, 12:10 AM   #3
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Well then the magnet just wont grab the bar, i was just wanting to slow down the fan speed without a potentiometer. I just need to know i'm not going to start any fires by hooking up a mismatched voltage.

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Old 11-02-2011, 12:22 AM   #4
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Mine works great with a 5V cell phone cord. I have a couple stir bars and the size of the bar makes a big difference as does the material/distance between your magnet and your bar.

I've made 3 stir plates with 5V cords and have gotten them all to work reliably with various stir bars.

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Old 11-02-2011, 12:24 AM   #5
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5V cords with higher voltage fans?

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Old 11-02-2011, 12:27 AM   #6
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Quote:
Originally Posted by blawjr View Post
Well then the magnet just wont grab the bar, i was just wanting to slow down the fan speed without a potentiometer. I just need to know i'm not going to start any fires by hooking up a mismatched voltage.
You won't start fires with a mismatched voltage, try a smaller supply and see how it works. I have a 0 to 12 v regulator and my 12v 80mm case fan starts spinning at around 3-4v.
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Old 11-02-2011, 12:39 AM   #7
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You can use a lower voltage power supply I don't know how low, like the OP said he uses a 5v supply. Or just put in a fan control of some sort will do the same

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Old 11-02-2011, 12:48 AM   #8
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The lower the voltage, the slower the fan speed right? Thats basically what a potentiometer would do right? Lower the amount of current running to the fan?

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Old 11-02-2011, 02:53 AM   #9
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My stirplates use 5v power supplies with 12v computer fans. It's fine.

And yeah it won't spin as fast.

I also broke the blades off my fans, I thought it wouldn't be good to have that much air moving around inside the box. Prolly doesn't matter tho.

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Old 11-02-2011, 04:39 PM   #10
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I found that when I built my stir plate and was having this problem it wasn't my voltage I had tried anywhere from 3.9 - 12 vdc with a potentiometer. I then thought get my magnets on the fan closer to flask to help make stronger field no work either. Then I lowered my magnets away from the flask in my stir plate and found the sweet spot no more throwing the bar. Now I have 5 vdc power and can crank full speed if need be and not throw the bar. You may start by getting your flask or jar with water and stir bar and set some books or something of different heights on each side of flask to create a different height to internal magnets in your plate and try and find that sweet spot. Hope this helps

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