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

[TBaGZ]

So I am taking my turn and putting together a stir plate... Originally I was going to use a 9v power supply, but it won't turn the fan. The fan is marked 12v, but I figured it would just spin slower. The only other PS I have is 19.5 DC, this spin the fan just fine. The problem is when I wire in the rheostat for speed control. It doesn't do anything. Is a 25ohm 3W too small for this PS, or did I wire it wrong? I went neg on fan to neg on PS, with pos on fan to outer leg of stat, and center leg of stat to pos on PS.

I want to get the wiring all figured out before I start mounting anything.

 

[TBaGZ]

OK.. I found a 9v PS that was able to power the fan, but my rheostat still is not working. I have power from the PS going to the middle post, and the leg on the right going to the fan (this all the positive side), with the neg going directly from the PS to fan. Should this not work?

 

[troyh]

OK.. I found a 9v PS that was able to power the fan, but my rheostat still is not working. I have power from the PS going to the middle post, and the leg on the right going to the fan (this all the positive side), with the neg going directly from the PS to fan. Should this not work?

Sounds right but the rheostat is probably providing too high a resistance so it stops the fan completely. You can wire in an LM317 voltage regulator to provide more voltage but allow the rheostat to dial the voltage down from the full voltage. This thread has such a wiring diagram.

Note that some fans require a higher minimum voltage than others.

 

[TBaGZ]

It's not that the rheostat stops the fan, it doesn't seem to slow it down enough.

 

[TBaGZ]

So yeah, this rheostat is a dud, going to get another one. I picked up a few resistors and and if I put one in line instead of the rheostat it slows down like it should.

 

[troyh]

So yeah, this rheostat is a dud, going to get another one. I picked up a few resistors and and if I put one in line instead of the rheostat it slows down like it should.

Oh, then it doesn't provide enough resistance, it's not defective. Look into ohm's law to figure out how much resistance you need.

 

[TBaGZ]

I was thinking that, but when I put a 10ohm 1w resistor inline it slows down. So why wouldn't the 25ohm 3w stat work?

 

[troyh]

I was thinking that, but when I put a 10ohm 1w resistor inline it slows down. So why wouldn't the 25ohm 3w stat work?

It probably did, just not enough to notice the difference. Testing my basic understanding of ohm's law....

Let's say your fan is 12V and .5A. To drop the current in half (.25A), you'd need a 48 ohm resistor. Just the 25ohm rheostat cut the current to .48A (12 / 25), so it barely did anything, only 4%. Adding a 10ohm resistor cut the current to .34A (12 / 35), or 32%, which may be enough to notice.

 

[TBaGZ]

I'm talking the 10ohm resistor without the rheostat made a noticeable difference.

 

[troyh]

I'm talking the 10ohm resistor without the rheostat made a noticeable difference.

Don't know what to tell you then. Maybe you're right and the rheostat is defective, although that seems unlikely if it's new. Or maybe the 10ohm resistor is a 100ohm resistor (translating those color bands can be error-prone)?

 

[TBaGZ]

Yes, it is a 10 (just took it out of the package). I also put a 100 inline and that made it too slow. I will just pick up another rheostat and try it. Maybe I should get a higher ohm one? Could it be that when I initially put it to the 19 volt PS I fried it?

 

[troyh]

It's possible, I guess. Did you notice it being hot or smelling burned? May as well try another rheostat.

Out of curiosity, what are the specs on the fan?

For what it's worth, a slow spinning stir plate is better than a faster spinning one. I keep mine at 25-30% speed at the most. When it gets too fast the stir bar gets spun off easily. You don't need a huge vortex, you just need to keep the liquid turning with a small dimple to get air into the solution. So the 100ohm may work well by itself, i.e., without a rheostat.

 

[TBaGZ]

So I was messing around with magnet placement and whatnot with just using two sided tape for temporary mount until I knew where I wanted them permanently placed. As you see the magnetism pulled the stacks together and layers them down. So I figured what the heck and gave it a try. Seemed to work pretty good. Figure I will just have to raise it up closer to the lid, but that's it. Anybody ever put their magnets laying down?

 

[TBaGZ]

Btw the fan specs are 12v .16a.

 

[Kirch3333]

Just build a stirplate using this thread as a guide and it turned out awesome! Very very quiet. the only issue I had was that I bought a computer fan that came with a rheostat but I was unable to use the rheostat because of the way it was built (with little circuit boards attached). Now all I need is a flask... How many more days til Christmas?

 

[bd2xu]

Does anyone have a good method for centering a washer (to be glued) on the fan? I've built a stir plate but having a hard time getting the washer centered so the fan is wobbling quite a bit.

 

[Kirch3333]

I've heard if people using a 60 second epoxy so that they have time to adjust it before it sets

 

[bd2xu]

I've heard if people using a 60 second epoxy so that they have time to adjust it before it sets

That could work so set it, turn it on for a second to get spinning, adjust. I used krazy glue last time... Nope

 

[Roadliner]

Built it.. Turned out awesome and is spinning away a starter as we speak

Just build a stirplate using this thread as a guide and it turned out awesome! Very very quiet. the only issue I had was that I bought a computer fan that came with a rheostat but I was unable to use the rheostat because of the way it was built (with little circuit boards attached). Now all I need is a flask... How many more days til Christmas?

Nice on making the removable part the top! Wish i would have thought of that.. could have saved me a whole lote of trouble with how many times I had to pull it apart to get it just right.

I've heard if people using a 60 second epoxy so that they have time to adjust it before it sets

I used a 5 min epoxy.. let it set for a minute so it was slightly tacky and then fine tuned till my hearts content. Worked well for me.

 

[evolcoms]

I am looking to build one of these, but I wanted to check and see if anyone had a couple magnets or one hard drive magnet they would sell?

 

[Roadliner]

The ones linked to from the OP work really well.. quite pleased with them.. I'd recommend getting 4 though so you can double the power for larger stir bars... has a tough time holding onto a 2in

 

[bd2xu]

I'm using four magnets from two hard drives, and they will spin a 1 inch perfectly but not a 2 inch. However the 1 inch bar with a 12 V adapter has no problem stirring a 2 L starter in an Erlenmeyer flask. When I use a 9 V adapter it's not enough power and the bar gets thrown. I've learned in making this that no two are alike, there are a lot of factors in play and you really have to tweak it to get it just right. I'm using a cigarbox and what I'd like to try next is to cut out a square or circle in the lid to reduce the material between the magnet and the glass bottom. I'm hoping this will get better contact And a more powerful connection between the magnets and The stir bar

 

[Huaco]

I am looking to build one of these, but I wanted to check and see if anyone had a couple magnets or one hard drive magnet they would sell?

Man... Go down to your local 'craft' store. Michaels, Hobby-Lobby etc. They have packages of 6 rare earth magnets for a few bucks.

 

[evolcoms]

Man... Go down to your local 'craft' store. Michaels, Hobby-Lobby etc. They have packages of 6 rare earth magnets for a few bucks.

Hmm , ok ill have to go check them out.

 

[evolcoms]

So I went to all my Radio Shacks, and home improvement stores and they didn't carry to right size magnets. Here is my Stir Plate....minus the magnets :/
Top view



Bottom view



Side view


Thanks for the great tutorial!

 

[Huaco]

Try your local hobby/craft stores. Michaels or Hobby Lobby

 

[Roadliner]

The clear case is a sweet touch

 

[evolcoms]

The clear case is a sweet touch

Thanks!I found the case at walmart in the craft section with all the beads and jewelry equipment. I was going to for the " Look at my work" look. My dad has worked in electronics (Qualcomm) my whole life so I'm sure he will be happy with my little gadget. Although, i didn't do much, but follow instructions.

I also went to my local Michaels and they only had flexible magnets.

 

[bizarrojosh]

Thanks! I was going to for the " Look at my work" look. My dad has worked in electronics (Qualcomm) my whole life so I'm sure he will be happy with my little gadget. Although, i didn't do much, but follow instructions.

I also went to my local Michaels and they only had flexible magnets.

Where did you get the clear case?

 

[evolcoms]

Where did you get the clear case?

Walmart. Where they sell beads and jewelry making equipment. I also saw them at Michaels. Same general area.