DIY Stir Plate HELP!

Hello. I am trying to build a DIY Stir Plate. I have the fan and AC Adaptor pictured below. The fan does not spin, it only shudders when powered. I will admit to knowing next to nothing about electricity. Can someone smarter than me tell me what my problem is? Is the adapter under powered? If so, what power do I need?
Many thanks to all those one these forums that share their knowledge.

The adaptor is underpowered. It's power output is rated at 9 volts of direct current and that fan runs at 12 volts of direct current. Look for another power adaptor or pick up a voltage switching multi-adaptor at radio shack and set it to 12 volts.

The adapter may be fine since you won't need the fan at max speed.

How are you connecting the fan to the power? Do you have a polarity issue?

harrke said:

The adapter may be fine since you won't need the fan at max speed.

How are you connecting the fan to the power? Do you have a polarity issue?

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If it doesn't run at all, switch the wires and try. Unplug first. I had to put a rheostat on to reduce the power and slow the fan.

You are under in amp's (current). You need to up those but do not go over the desired 320mA. You need to either solder a current amplifier transistor or look for another power source or new fan. Try and look more closely at the amps as that is what will drive the fan, also look to install a potentiometer to help control the speed.

Thanks for the quick replies. So I did switch the wires. I am direct wiring to test prior to placing in the project box with a potentiometer. I also have a output: 12VDC 1000mA adapter. I hooked that up and again the fan is powered but does not spin, just shudders. Uggh...

Alright, so not a polarity issue…

Next, with the wires connected and the fan shuddering, give a spin by hand.

If you can start the fan by hand, the 9v transformer is too small. But, using the 12v, you may need something like a rheostat to slow it down.

So that fan is rated at 12Vdc 320ma - at little Ohms law tells us that it's approximately 37.5 ohms.

Your wall wort is rated at 9Vdc 200ma. When you put a 37.5 ohm load across it, it will try and pull 240ma.

I think you need a different adapter.

unless your using a potentiometer 12v and even 9v may be too fast... I use a 6v battery charger for my 12v fan powered stir plate and even that is very vigorous ... I'm adding a potentiometer I also found the magnets can mess with the fan motor causing it to need more current to run correctly. I had to flip my magnets over to change the polarity or my fan just sat there vibrating since the polarity of the fan motor was being effected.

augiedoggy said:

I also found the magnets can mess with the fan motor causing it to need more current to run correctly. I had to flip my magnets over to change the polarity or my fan just sat there vibrating since the polarity of the fan motor was being effected.

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What he said.
If you try it with your 12vdc adapter and are still getting the same result. Try it without the magnets in place if it isn't too late. Get the fan working first and go from there. I've found that some fans are very sensitive to the magnets and don't like to work at all with them on there. Also, I gave up on hard drive magnets as they were always a pain to get balanced and positioned perfectly to keep them from throwing my stirbar. Now I epoxy a huge fender washer to the fan first, then I can position my approx. 1/2" round rare earth magnets where they're best suited and glue them down when I find the best spot.

You'll also need a potentiometer on there or some sort of way to reduce the voltage going to the fan. As mentioned before, a full 12v and sometimes even 9v is too fast most of the time.

FYI, radio shack sells rheostats but know reading this thread, they're actually potentiometers because they have 3 connections whereas I just read rheostats have only two. I have what I thought was a rheostat in my stir plate but it has 3 connections. If I recall, I'm not using all three connections so a rheostat should also work.

My first power adapter wasn't enough to run the fan with magnets. Definitely find another adapter and solve speed issues with the potentiometer.

blkhrt said:

You are under in amp's (current). You need to up those but do not go over the desired 320mA. You need to either solder a current amplifier transistor or look for another power source or new fan. Try and look more closely at the amps as that is what will drive the fan, also look to install a potentiometer to help control the speed.

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I know almost nothing about how the components work, so this is interesting. You're saying you could use a lower power adapter and add an amplifier to get what you need? Do you find the amplifier in the same little drawers at Radio Shack? I have found a bunch of 5v adapters, but they wouldn't turn the fan. So maybe this is a solution?

The easy method would be to just get a multi-voltage transformer from radio shack. With the voltage selector on that, you'll be able to control your fan speed easily without all the electronic tinkering.

http://www.radioshack.com/product/index.jsp?productId=3875403

krazydave said:

The easy method would be to just get a multi-voltage transformer from radio shack. With the voltage selector on that, you'll be able to control your fan speed easily without all the electronic tinkering.

http://www.radioshack.com/product/index.jsp?productId=3875403

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But that's $17.I found a $5 cord at the dollar store that says 6.8-8v. It's not adjustable, but that's what it says on it. Cell phone charger in bright green.

Still, even if you're buying all new parts, it's still way cheaper than buying one already made.

When I did my stir plate I had to space the magnets from the fan with a 1/2" wood disk cut with a hole saw. Powered with a variable voltage wall wart. 3V spins it just fine. 1.5V and it doesn't turn.

Well, I caved and just ordered a Stir Starter stir plate. Ironically it cost $3 less than what I spent at Radio Shack. Although I will not have the satisfaction of having built it myself, it will help my starters, which are required because of the way I harvest yeast. Many thanks to all who posted suggestions here. This is a great group!

there are some threads that use this fan from Amazon.

If you DC fan has three wires, one wire is a speed controler and will require some sort of signal to run the fan. If you can find a DC fan with two wires you'd be in business.
I think the appeal of the USB fan from amazon is it has the speed controler built in, you just need a 110VAC/USB adapter like most smart phones use.

FortMillBrew said:

Well, I caved and just ordered a Stir Starter stir plate. Ironically it cost $3 less than what I spent at Radio Shack. Although I will not have the satisfaction of having built it myself, it will help my starters, which are required because of the way I harvest yeast. Many thanks to all who posted suggestions here. This is a great group!

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I think it makes sense if some of the parts are harvested from old computers, etc. Otherwise, that's a cheaper option. I'm surprised at how cheap, though!