Quick stirplate question

[Cheesy_Goodness]

First stir plate build here...

I've got my 12v PC fan wired up to a 12v AC adapter and earth magnets from an old hard drive in the center. The problem is, it's spinning too fast and my stir bar can't keep up and ends up being thrown against the side of the flask.

Essentially, I need to slow the fan down. I've read that a potentiometer will do that, but I'm looking for a quicker/easier solution as I don't have an electronics store in my immediate area.

Can I rig something up to slow down the fan or am I going to need a potentiometer?

 

[baseballsmitty]

The only way that you can slow the fan down is to either reduce the input voltage or add some type of series resistance into the circuit.
The easiest way to do it is to add a potentiometer - this will also give you some ability to adjust the speed on the fly. If you don't have an easy way to get a potentiometer or small resistor you could try to use a different AC adapter. When I built my stir plate I was able to find 6V, 9V, and 12V adapters just sitting around my house.

Sent from my HTC One X using Home Brew mobile app

 

[BlackenedBrew]

I ended up using the potentiometer AND a lower wattage AC adapter. The adapter I had planned to use was just too much, and when I found a smaller one (wife used to work for a cell phone company) it helped a lot. I don't know off hand what size I ended up using, but when the potentiometer is on full blast, I get a good speed. I can try to remember to look at it tonight and let you know what size worked for me.

 

[augiedoggy]

this is where years of collecting a drawer full of about 40 powersupplies from various dc powered devices can come in handy... I too had issues...I used a 6v/12v motorcycle float charger and it works on 6v but can still throw the spinbar so I ordered a little pwm board for $5 from ebay.... now that I think about it I should have just hit radioshack for a potentiometer...

 

[aslander]

I used this fan with a 12v charger and a laptop HDD magnet

http://www.amazon.com/gp/product/B00066ISVG/?tag=skimlinks_replacement-20

It has a switch for 3 speeds wired in already. You have to start it at the slowest speed.

You may also want to check and make sure the magnet is centered on the fan, otherwise it will throw the bar. The easiest way is to drop the stirbar onto the magnet a couple times until you see the spot that it tends to land. Then leave the stirbar on there and try to center it by using the stirbar as a visual. I had problems with mine being thrown because I had centered the magnet, but the stirbar was not centered on the fan because of the way the magnets would line up.

Hard to explain, but if this isnt clear I can try to ellaborate.

 

[PaintedRat]

I replaced my drawer of spare misc power supplies with a Radio Shack adjustable voltage power supply. I use the one cord for stir plate, kitchen scale, and a few misc things. The voltage switch is in 1.5v increments which I find to be sufficient. For the stir plate, I end up using 6v for a small step up starter, and 7.5v or 9v for a 2L starter. I built my dual stir plate with potentiometers, but I think they're less useful than the adjustable power supply.

 

[Cheesy_Goodness]

Thanks for the replies everyone.

It looks like I'll need to poke around and look for some old cell phone chargers.

In the mean time, what potentiometer should I look in to? I did a quick search on radio shack and it looks like they carry mostly audio potentiometers. Is there a difference between an audio potentiometer and what I need for a stirplate?

 

[masonsjax]

I used a light dimmer switch for mine. Soldered a power cable through the switch and to the legs of my charger. Works great. Just another option if you cant find a pot somewhere.

 

[TopherM]

You can just put one or two simple resisters inline between the power supply and the fan. About $0.40 each at Rat Shack. That's what we did in my club's group build, and it works like a charm!

 

[augiedoggy]

I replaced my drawer of spare misc power supplies with a Radio Shack adjustable voltage power supply. I use the one cord for stir plate, kitchen scale, and a few misc things. The voltage switch is in 1.5v increments which I find to be sufficient. For the stir plate, I end up using 6v for a small step up starter, and 7.5v or 9v for a 2L starter. I built my dual stir plate with potentiometers, but I think they're less useful than the adjustable power supply.

I actually have one of these.... but its easier and more convenient to just use the free ones I've accumulated than risk forgetting to change voltage or polarity or having to run around the house and find what device is currently using it and steal it from there.... I can run my stir plate AND my scale at the same time while charging my tablet and listening to my satellite radio and powering my router for internet....you get the idea... plus if one of those devices fails like my brand new xbmc android box powersupply did five minutes after unpacking it I found I had 4 spares that provided more amps which helps the stability I've read...
but yeah that adaptor works fine too...

 

[augiedoggy]

I used a light dimmer switch for mine. Soldered a power cable through the switch and to the legs of my charger. Works great. Just another option if you cant find a pot somewhere.

I did exactly that on my HLT keggle stirbar setup but that also uses a 120v fan to spin it...

 

[Cheesy_Goodness]

The resistor sounds good but I'm kind of liking the light dimmer idea.
But, my guess is I would be limited using a 12v fan and a light dimmer meant for 120 volts. Is that right?

 

[masonsjax]

Yes that's what I did.

 

[BlackenedBrew]

Hey, I'm sorry it took me so long to reply, but I looked at my adapter last night. I'm using a 12v AC adapter along with the potentiometer.

 

[Cheesy_Goodness]

Thanks man.
I'm going to poke around Home depot this week fora a cheap light dimmer and report back.