My Stirplate... Cheap and Easy Build...

[Flomaster]

ZOMG... so after spending HOURS trying to get mine working and was never really happy with my results. I ended up buying this $11 plug in play solution....
https://www.homebrewtalk.com/f11/building-stir-plate-check-out-usb-adjustable-computer-fan-253254/

I am using my same wooden box I used for my stirplate and the power supply, but this time I have control of my speed. and I can slow my fan to a crawl or get the vortex touching the bottom of a one gallon pickle jar.

-=Jason=-

 

[mkakunda]

looks pretty straightforward. cant wait to build this soon

 

[Accidic]

I got swindled out of my old built one and have to build another. On the plus side I've got a stronger fan and at worst I might have to buy another Potentiometer if the one I scrounged is weak.

That said, I was toying with the fan I had sourced for it (140mm ancient beast) with a good incredibly stout motor on it. Only problem is I don't seem to get a lot of effect with varying the voltage like I did on my previous one. Has anyone experienced something of this sort? It kicks on at around 5V or so and this RPM stays approximately the same all the way through 12V (it's max rating).

Additionally I've discovered I'm out of old SCSI drive magnets (which are absolute kings for this btw with either 1 or 2" stir bars easily up to nearly an inch away and I don't remember them ever getting thrown) so I was going to use a few of the crappier hard drive magnets. How much added magnetism are you getting stacking these because while a nightmare to pull apart they don't seem to be that much of an improvement in field strength but maybe it's just my imagination. Any particular brands work better than others per chance? I have literally hundreds of em. (Have to dismantle and hardcore destroy every platter on a drive that fails here so might as well salvage the magnets $.

Lastly, on my previous build I put a couple resistors on either side of the ends of the Pot to ensure a minimal divide of my power source (I've got numerous 24V with great power out) to split it from the getgo and then I use the Potentiometer simply as a voltage divider. My electronics theory is getting a bit fuzzy/rusty from lack of use but is there any reason they can't simply be used as a voltage divider? That would shut off the fan at the low segments and negate the need for a switch anyway. The only thing I can think of that might cause problems is at the lower end of the pot the current would spike on the smaller divide but it seems like the reduced voltage would prevent this from being an issue anyway. Was thinking about going this route this time anyway til I found out my stupid fan doesn't wanna cooperate. May just say screw it and just try to source out an AC door cooling fan.

 

[Accidic]

Turns out that fan was only variable of a few percent adjustment at best. I used two different fan controls (commercial) that had the same result but adjusted a couple 80s with same pin out just fine. Even broke outre the bench ps with the same results. I wonder if that'd the source of some of the reported issues with the rheostat setup...

That said came out well although I still have some concern about violent agitation. Will drag a 3/4 inch whirlpool to the bottom with heavy bubbles at 1L, ~1/4 inch with intermittent bubbles at 2L, 3/4 to bottom in 2L plastic pitcher (w/0.25 elevated lip), and 1/3 to bottom in gallon jug. Still don't like the lack of control but looks ok in computer speaker box I guess.

 

[acefaser]

Thank you so much for the info on how to build the stir plate. Here is my build.
I cut the fan blades off to keep the 'drag' down for the fan. I was worried that the fan would be out of balance, but spun just fine with my cut off blades. I used 6 'super magnets' from Ace (3 per side). Those magnets are very strong and I could have gone with less but I was using 1/2" spacers for the fan and 3 magnets fit perfectly. I was using a 9v power supply and switched it out for a 12v. I would highly recommend the 12v. It spins the 2" bar faster.

I also only had 1 1/2" #6 screws and they wouldn't go through the fan and 1/2" spacers so I ended up cutting a part of the fan mount away to fit the nut. It worked perfectly.

Finished product:

In action:

 

[pericles]

I just built mine, and I love it. The first thing I did was to start experimenting with stir-bars. . . they have one inch, one and a half inch, two inch. . .

It just occurred to me yesterday that, instead of hunting all over creation to find magnets - or prying them off a hard drive - I could have just used a three inch stir-bar glued to the fan.

Just figured I'd pass along my revelation.

 

[rlynge]

Maybe this has been brought up already but when I get the connector end off of my power supply I noticed that all I have is two black wires. On one side there is grey shading on the outside of the wire and then the other just has some gray printed words that show 80c 300v etc.....Which is the ground?

 

[emjay]

There is no ground

 

[Accidic]

Ground doesn't really have anything to do with your ps (presumably wall wort?). One is positive, the other negative assuming the output is dc. Ground is really only for safety reasons and frequently isn't what most people think it is in most cases.

 

[rlynge]

Thanks for the quick reply! How do I know which is positive and which is negative?

 

[TrainSafe]

Easiest way is to put a volt meter on it.

Otherwise if you don't have anyone you can borrow from, just hook it up. With 5 volts dc, it isn't a safety issue. It will run backwards one way (reversed polarity).

 

[Accidic]

Use a multimeter. You can frequently get a cheap one at harbor freight for like $3. Any crappy one will do tho. Analog or digital doesn't matter.

 

[rlynge]

The fan is supposed to run clockwise right....so if I get it backwards it would run counter right? This means I could reverse it. Does it even matter which way the fan turns? I am using a 12vdc power supply.

 

[Accidic]

Depends on the fan. Mine won't turn in one direction depending on polarity. The one I used previously wouldn't either. It just depends on the design. Mine were larger more expensive fans tho. If you plug it up and out doesn't turn with no load unplug and switch the leads and you'll probably be fine even if you have a fan that prevents counter rotation.

 

[Catt22]

Thanks for the quick reply! How do I know which is positive and which is negative?

You will know you have it right if the fan runs. If it doesn't run, reverse the wires. It won't do any harm if you have it backwards on the first try, it just won't run.

 

[Accidic]

If it runs your fine. I don't think most fans are set up to matter. It's cheaper to just let the electromagnetic field control the direction. They just usually are capable of less torque.

 

[emjay]

I've never had a fan which actually ran backwards (I've tried with 3 of them). Either way, there's no harm in trying to connect them both ways.

 

[Accidic]

Jinx!

 

[rlynge]

Tried it and it worked....thanks guys! I will finish the build soon!

 

[Accidic]

Hope you have better luck balancing than I did. My new plate is neither adjustable nor well balanced.

 

[rlynge]

Well I think I am going to do what Jakecpunuts did and use velcro to attach the washer. That way it should make it easier to adjust the balance.

 

[Accidic]

Is great if you have the room. My tolerance was really thin. With magnets I have less than 1/64" to the top of my box.

 

[rlynge]

We shall test it out and see....I have to go pick up some bolts, velcro, and some spacers to finish it. I might pick up some slow setting epoxy just in case. I am using a fan from an old dell(2001)....hopefully it works well enough!

 

[rlynge]

So while I was at publix I just so happened to see some velcro. Of course I bought it so that I could work on my stir plate some more. I got my washer set in a pretty balanced manner. I was going to use the magnetism of my HD magnet to attach it to the washer but the fan throws it off. Should I glue it or should I buy some of the magnets suggested by the OP?

 

[integra93ls]

nice

 

[rlynge]

Bump

 

[barrooze]

After centering my washer on the fan, i glued it on then I used that tacky putty you can use to put up posters to get the magnet centered. Using tuis putty allowed me to move the magnet around and start up my stirbar to make sure it won't get thrown. The magnet is actually so well attached to the washer with the putty, I haven't glued it down.

 

[Accidic]

There two different magnetizing types used on hd magnets. Some I pulled out of a scsi drive were perfect axial setup so I used one on each end. The recent one I built I had to snap some hd magnets in half but stacking have the power I needed. Alternatively many on here have bought disc or bar magnets with great results. I hear balancing is easier doing that. It just depends on your budget and/or need are. I'm broke atm so my total investment (other than the stir bar that I already had was $0.28 cents.

 

[rlynge]

Maybe I will snap mine in half and give it a try. Worse thing that could happen is that I need to by magnets. The thing that kills me is that the magnets are wicked cheap but then they rape you on the shipping. A $2 magnet costs $8 to ship. That doesn't make sense.

 

[Accidic]

The target is to have north on one side and south on the other. TBH I don't really understand why the halves work better but I tried a singles, doubles, and halves (both single and double) and only my old axial mags were better than the doubled halves.

Edit: Please note, the halves were magnetized through the length of the magnet rather than through the thickness (aka axially). I thought when you snapped them in half the north side near the south end then becomes the south end but it doesn't seem to act that way for me.