Homemade Stir Plate - Lessons Learned & Tips

I have read some of these at various locations and finished assembling a homemade stir plate with the common parts people can harvest from old computer parts, old cell phone, etc. This isn't a documented "How to..", there are plenty of them here that are excellent, rather a, "I did this, and heres something to do different, don't repeat my mistakes."

Thought I would put together my experiences while they are still fresh in my head and the blood blister on my finger is still throbbing. But as a side note, remember, this is REALLY cheap and easy and I would still recommend it if you make yeast starters. And if you don't make yeast starters.....start making yeast starters.

So the common parts needed simply put are:

Power Source - Cell phone charger, Computer power supply, or buy one at Radio Shack
Stir Plate - Computer Fan (most common)
Magnets - Computer Hard Drive (Rare Earth magnets)

Stir bar, Flask, Glass container, etc...easy to find online or LHBS

If you have an old computer lying around, you have everything to make this with little to no wiring necessary. The reason i like the power supply from a computer is that it is already wired to plug in fan or fans. No wiring needed, just plug in the 4 pin male to female connectors. Done. If you don't have an old computer, go to your IT department at work or large business. They either have a boneyard of old crap or they throw stuff out routinely. Ask for an old power supply, case fan(s), and a couple hard drives. It is entirely expected that they wont give you old hard drives, but ask if you could take it apart in front of them and get the magnets. Or even offer to drill a hole through the plates. This is what we do before we dispose of them.

The magnets. DON'T underestimate how powerful these suckers are. If you have two they WILL snap together so hard they will pinch your fingers. Like immediate blood blister pinch. The stupid part is I work in IT and I KNOW how strong these these are and despite my careful handling....DAMN...snap...ouch.

I used JB Weld to adhere the magnets to the hub of the fans. Let the JB Weld cure before trying to add another magnet. It isn't strong enough to hold against the force another magnet in near proximity.

I think thats it. Just wanted to tell another example of how easy it is to make these. All the parts are in a scrap computer. Have fun.


MNBugeater

The best lesson's I learned were,

1.) One magnet centered on the fan hub is more than enough to grab the stirbar provided you have the magnet close enough to the surface of the enclosure box.

2.) A simple rheostat is all you need if you have an AC power supply that is adjustable to 1.5, 3, 4.5, 6, 7.5, 9 and 12 volts. If you need to slow down the fan, simply switch to a lower voltage. ACE Hardware had this AC power supply for $13. Not bad.

3.) Slide an O-ring from a dip tube on the stir bar and center it. It acts as a spin point and works well.

4.) Find out where people drop off their old PC's in your area. I went to our city recycle yard with a screwdriver and a side cutters and got fans, hard drives, and on/off switches for free.

Cookiebaggs said:

2.) A simple rheostat is all you need if you have an AC power supply that is adjustable to 1.5, 3, 4.5, 6, 7.5, 9 and 12 volts.

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Best idea for simple speed control that I've seen to date!

What works best, spinning the bar faster or slower? Thanks - Dirk

once again sorry for the noob boob.....but what is this for? Yeast starters? You just mix your starter and let it spin for a couple days?

Is that the only thing its for?

ApolloSpeed said:

once again sorry for the noob boob.....but what is this for? Yeast starters? You just mix your starter and let it spin for a couple days?

Is that the only thing its for?

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Yep, helps the yeast grow by giving them more oxygen and keeping them in suspension. Search stir plate, and you will find more info than you will ever be willing to read through. Including my how to w/ pictures.

WOW! I have been pondering starters. i know what i am doing in the morning!

On lesson I learned is that a stir bar is needed (at least for me).

And two, is that I first used very strong magnets from a magentic nametag. They were likely earth magnets already attached to a plate. Problem was they were not 'reversed' or flipped so it was both positive sides up. My stir bar wanted one side but was 'afraid' of the other. When I replaced it with a hard drive magnet it worked like a champ.

Third, was not to put the magnet too close to the top of the box (on my plastic project box from radio shack). When I spaced it about 1/8 inch away from the top it spun faster and seemed to work better.

Good luck to others building.

For mine, I used a cast-off A-B printer switch for a housing. I mounted the speed control (simple potentiometer) right where the selector was, and the on-off right next to it.

There are likely to be many of these things floating around in IT departments collecting dust since everyone is now networking their printers instead of sharing them. Problem might be finding some that are not already thrown away.

Cookiebaggs said:

2.) A simple rheostat is all you need if you have an AC power supply that is adjustable to 1.5, 3, 4.5, 6, 7.5, 9 and 12 volts.

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A simple model train transformer works well for me. Had several sitting around.

I actually had a great DIY stirplate that I made from a cigar box and some old computer stuff. The only problem is my stirbars became magnetized because I kept them inside the cigar box for storage. They inevitably "found" one of my extra earth magnets (used to keep the stirbar stuck to the flask when pouring) and became magnets. Now they don't hold to the magnet well and end up spinning right off as soon as I turn it on. I checked the web and can't find a way to "un-magnetize" the stirbars. I guess I can chalk this up as another lessons learned. They are now stuck to my kegerator and actually hold really well.

tomasej said:

I actually had a great DIY stirplate that I made from a cigar box and some old computer stuff. The only problem is my stirbars became magnetized because I kept them inside the cigar box for storage. They inevitably "found" one of my extra earth magnets (used to keep the stirbar stuck to the flask when pouring) and became magnets. Now they don't hold to the magnet well and end up spinning right off as soon as I turn it on. I checked the web and can't find a way to "un-magnetize" the stirbars. I guess I can chalk this up as another lessons learned. They are now stuck to my kegerator and actually hold really well.

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This is odd. All my stirbars are magnets and have always been so. They stick to eachother end-to-end. I thought this was necessary for them to be held by the driving magnet. Your'e saying that yours were not magnets at one time?

AFAIK, all stir bars have a magnet embedded inside. They should be stored in pairs stuck together to help preserve their magnetic properties. I have yet to see a stir bar that was not magnetic, but from what I've heard, they can lose or weaken their magnetic properties if subjected to strong shock such as if dropped repeatedly. Thrown stir bars are usually an indication of poorly aligned or spaced drive magnets. Stir bars can be damaged though, so that is a possibility, but I doubt that the problem is due to them suddenly becoming magnetized when before they were not.

agreed. Mine stuck to each other right when I got them. Ordered 2. Seem to work.

My stir bars are all magnets. In a pinch, a piece of plastic coated steel works, but not nearly as well.

IrregularPulse said:

agreed. Mine stuck to each other right when I got them. Ordered 2. Seem to work.

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I once bought a pair of stir bars and the package had instructions recommending to store them stuck together. They were packaged that way too. I'm not making this up!

All,

Thanks for the feedback. I guess I thought that was my "smoking gun" and did not look anymore into it. If they were always magnetic then I wonder what has gone wrong with my stir plate. The thing worked great before and now all of a sudden it's throwing stir bars. I might try replacing the rheostat next. Thanks again.