wiring a computer fan stir plate

[paul m]

I've slowly scrounged bits to make a stir plate. The fan is rated 12v DC .18Amp- recycled from a stuffed computer. Wired that to an old 12v phone charger. works/ spins a treat. I bought 2 x 25mm stir bars from brewers coop- taped one to the centre of the fan the other bar is for my starter. The stir bar in the starter throws to the edge rather than spinning/stirring. I tried using a jar but its convex on the bottom then tried a beer jug with a more concave bottom, still not spinning. Designs I've seen on YouTube use a potentiometer to vary the speed of the fan. I notice commercial products have a speed knob. what rating should the potentiometer be? Does anyone have a wiring diagram thats easy to follow for a chimp. Is the potentiometer essential? any other recommendations?

any other advise appreciated. Close to the end of my tether and start searching to buy one but then $100 plus sobers me up a bit!!

[G S]

I used these magnets
http://www.trademe.co.nz/a.asp?id=615289124. I glued them to a disc of mdf, atvspacing and polarity to matchnstir bar, then glued that to the fan hub,

And this for speed control, took about 10days to get here.
http://www.ebay.com.au/itm/White-Dimmer-Brightness-Adjusting-Contro...

Works a treat, I do have a flat bottomed flask though.

[Dan]

Hey Paul, I got some round rare earth magnets from Arthurs Emporium in town, glued 3 of them in a straight line on top of the fan.

For a flask I just use a 1.5lt coffee plunger inner - you can pick them up cheap from Briscoes - I got one for $5.

Try Jaycar for the speed variable adjustment. I bought the fan with control there for about $20.

[paul m]

thanks Dan, after a few more iterations i cloned most of your advise. I went to arthurs,bought 2 of their disk shaped magnet, not the brittle sort. I think its the rare earth ones. really effing strong about the size of a $2 coin. They were $4 or $5 each . They had quite a range of magnets i also bought some half penny sized ones- same material for 30cents each, but these didn't work for my seltup.  I dropped into compass computers and bought a fan with controller already assembled $25. Its a real butty fan and i found the butty magnets were slowing my original fan. It came with some rubber mount which were the clincher- anything to reduce annoying noise. Finally got it all working- just gluing into a box. I've managed to get it working using a range of ajee jars so don't need to try and source a thin glass option. Coffee plunger is a great idea to keep costs down. I think i've built the behemoth stirplate i reckon it could do a wheelly bin size starter!!!- photos to follow!

[Danny]

I used a couple of magnets out of an old broken hard drive that i got for free from a small computer shop.

For speed control i bought an LED Dimer Control of Trade Me for $8.50. I'd post the link but can't access Trade Me from work.

From what I read, the potentiometers from Jaycar are only rated at about .5 watts and will almost always burn out over time, most stir plate guides recommend at least 3 watts, I never found a cheap one of these though (hence getting the LED dimmer).

The wiring on the dimmer is straight forward too, 4 of those screw in type connectors, 2 in, 2 out.

[Grant R Baker]

+1, I use a single magnet from a hard drive, which is much stronger than a stir-bar... that is glued to the center of the fan. I didn't bother with a speed control, just an off on switch.

Flask sits about 3-5mm about the fan and works fine.

[Mike Cole]

Hi Danny, I realise this is resurrecting an old thread but I am putting together a stir plate using an LED dimmer control off Trade Me as you did. Just wondering how you wired it up? Im picking positive and negative from the power supply go into the pos and neg inputs on the dimmer and then the rest of the circuit is completed via the outputs (through to fan and switch and back to the dimmer). Is that right? Thanks.

[Hamish Jones]

Have a look on DX.com for fan speed controller, I got one for about $3.50 delivered.

If you need some rare earth magnets I can chuck some in an envelope and post them on up for you as I have a spare set at the moment that I scrounged out of a dead hard drive

[Ben]

Throwing the bar may be due to having too high a speed, particularly when you switch it on, rather than the container you are using.

I used this link http://aussiehomebrewer.com/topic/5191-tight-arse-stir-plate/page-22 to make mine. It has Jaycar part numbers so you can just bowl up there and get all the bits. It's a bit fiddly but I managed to do it without having soldered anything in years. Here's a link to my (not very useful) blog post on it - http://www.topofthehillbrew.com/stir-plate/

If you read through the thread on aussiehomebrewer you'll find out that using a potentiometer without the other bits in the circuit will burn the pot out quickly.

[Druid]

I had issues with the stir bar being thrown until I realized that I had to put the flask/jar containing the stir bar on the plate before turning it on.

Having some decent rare earth magnets on the fan will also help - they are extremely strong. It sounds like there are plenty of offers there for you to get some...

[Karl Hayes]

Hiya. I spent yesterday putting together a 4 post stir plate using an old computer for parts. As Druid says, the stir bar will be ejected fairly quickly unless you start the fan with the stir bar in position. Rip open a dud hard drive and use those magnets to attach to the fan. If it still isn't strong enough, stick the two hard drive magnets together and use as a single magnet. I've 3 different types of fan and none of them have enough grunt at full 12V to eject the stir bar. However when I tried 16V, yes it did happen. At 12V I was able to get a full vortex in 4L of water in a 5L conical flask on just one of the posts.

Also you should play around with different size stir bars.

If worse comes to worst - I sell the proper electrical item from my shop allgrain.co.nz but it's much more satisfying to get it right yourself.

[Chad Keven]

probably going too fast; I got a variable adapter from jay car electronics $25 it has a tiny dial that goes between 3v and 12v this is an effective way of controlling the spin when the slurry of yeast has grown thick sometimes it stops the fan; i can dial it upto 7v and it works Again this is a really easy way of controlling and wiring. i wired a switch in but it doesn't even need this