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Old 06-30-2007, 09:07 PM   #1
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Default Stir Plate Help

Hey guys,

I read the DIY Stirplate thread but I'm pretty electronicly retarted. I've got an old PC that I can steal the fan and magnets out of and a 5V cell phone charger but what else do I need besides a stir bar and a platform?

Do I really need a regulator and whatever to slow it down?

Thanks!

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Old 06-30-2007, 09:26 PM   #2
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Yeah, sorry to say that regulating the speed of the fan is quite important. I have to start mine slow and increase the speed if needed. I never can run it full blast as it throws the stirbar.

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Old 06-30-2007, 09:32 PM   #3
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If you're electronically retarded, you might want to rethink your strategy. You have to match the current sourcing of your power supply to the power requirement of your fan. And yes, you need to regulate the speed of your fan. There are several ways of doing it and some are far better than others. I prefer waveform 'chopping' over voltage regulation and would advise against voltage dropping over a resistor network.

Now, I'm speaking from the point of view of an electronics guy, not a stir plate owner/designer, so there may be some design parameters that allow voltage regulation without worrying about back EMF considerations. There was a DYI thread where a fellow successfully used a voltage regulator to control and just changed the bias to regulate the speed. He had success using that method but I'm wondering if he's limiting the life span of his fan by overheating it.

So, now that I've totally confused you, give me some faceplate details of your supply and your fan. I'll tell you if you can use them to do the job and you can see if it works without speed control.

*edit* Bender, you posted while I was typing. Was it your DYI thread that I saw? Does your fan heat at all with the lower voltage?

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Old 06-30-2007, 09:42 PM   #4
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Fingers, most of us use a voltage regulator circuit of some sort in our DIY stir plates. I haven't noticed any heating problems with the ones I've made.

I agree that just dropping voltage via a series of resistors/pots is probably not the way to go.

To further expound on the "electronic retard" theme - if you don't know what you're doing, and you don't understand schematics, please don't mess with electricity. 5-12VDC at low current draws is relatively safe, but even very low power circuits can overheat components and create smoke and flames.

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Old 06-30-2007, 09:44 PM   #5
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Cool, I'll break into the computer when I get home and let you know what I have.

I'm not opposed to a regulator or anything I'm just looking for an easy way to do it.

Is there anything else I could use from the computer?

Thanks guys

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Old 06-30-2007, 09:51 PM   #6
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Quote:
Originally Posted by greenhornet
I'm not opposed to a regulator or anything I'm just looking for an easy way to do it.
Find a speed controller for computer fans. www.newegg.com should carry a bunch of them for less than $10.
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Old 06-30-2007, 10:31 PM   #7
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Quote:
Originally Posted by Yuri_Rage
Fingers, most of us use a voltage regulator circuit of some sort in our DIY stir plates. I haven't noticed any heating problems with the ones I've made.
Yeah, I thought that was the case and in all honesty I'm not familiar with computer fan design. I can tell you that you don't want to drop the voltage input to an ordinary AC motor. You'll let all the smoke out of it. You want to use a thyristor (such as an SCR) in those applications. It reduces the current and the voltage so that you don't turn your motor coil into a really hot piece of wire.

So I hope I didn't add to the confusion. In the immortal words of Gilda Radner, "Never mind...."
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Old 07-01-2007, 12:12 AM   #8
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Yea. Once you let the smoke out, it's hard to get back in.

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Old 07-01-2007, 01:02 AM   #9
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Quote:
Originally Posted by Fingers
I can tell you that you don't want to drop the voltage input to an ordinary AC motor.
Most computer fans are DC. All of the ones I've used have been 12VDC models. There are some 120VAC computer fans out there, but they're more expensive so I never bothered with them.

You confused me a little when you started talking about waveform clipping - didn't know how you could do that on a DC circuit. Guess we're all on the same page now!
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Old 07-01-2007, 02:41 AM   #10
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Ok, so I've got an 8cmX8cm comp fan that is 12V 0.15A. It's currently mounted to a heat sink that came out of the comp...looks pretty neat. Especially if I can get a piece of plexiglass tomorrow for the top peice.

I've also got a Output: 12VDC 200mA power supply.

I ripped into an old harddrive as well and got out the magnet. Do I need 2 of these or will 1 do? I've got another HD if I need a 2nd but it was a bit of a PITA.

I hooked the power supply up to the fan and it spun fine... the reason for the speed controler is so the stir bar doesn't get thrown right?

Ok, so besides the obvious: stir bar, plexiglass, flask. What else do I need?

I'll check out newegg.com now...and try to get some pics of this hole thing when its done.

Any more info is apprechiated.

Thanks guys

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