Need Help With DIY Stir Plate

[Noflers]

I built a magnetic stir plate a few days ago, but I realized the CPU fan I used spins too fast for my 100 mL beaker. I picked up a rheostat from Radioshack, but I'm a bit confused about how to hook it up. Below is a picture of the inside of the stir plate, and the rheostat I bought:

 

[zoiDman]

I'm about the Last Person to consult on Electronics.

But would safe to Assume that the Negative is a Shared Pole? Like Maybe the Center Pole?

I guess it the Rheostat didn't cost much, you could hock up your Power source to the Left 2 Poles and then see what the Voltage is on the Right Pole with a DMM.

Might Fry things? I dunno?

 

[Noflers]

I got it figured out right after I posted this. Now, to find a switch for it. Lol

 

[zoiDman]

I got it figured out right after I posted this. Now, to find a switch for it. Lol

So what was it?

 

[Noflers]

You can connect to either the left terminal and the middle, or to the right terminal and the middle. The only difference between the two is it changes which way you have to turn the knob to increase or decrease the speed of the fan.

 

[JB69]

A buddy of mine made one of these for his beer brewing setup and I think he just put a regular momentary switch on his. He coated his magnetic stir stick with something too so the bare magnet wasn't in the yeast mixture. I'm not familiar with DIY liquid making, so I don't know if either of these ideas are desirable or not for this application...just thought I'd mention them.

 

[zoiDman]

You can connect to either the left terminal and the middle, or to the right terminal and the middle. The only difference between the two is it changes which way you have to turn the knob to increase or decrease the speed of the fan.

Gotcha.

I kinda thought that was what it was.

 

[Noflers]

A buddy of mine made one of these for his beer brewing setup and I think he just put a regular momentary switch on his. He coated his magnetic stir stick with something too so the bare magnet wasn't in the yeast mixture. I'm not familiar with DIY liquid making, so I don't know if either of these ideas are desirable or not for this application...just thought I'd mention them.

The stir bar (magnet) I have is encased in some sort of coating, not sure what, maybe Teflon or something.... And yes, I brew beer as well and I'll definitely be using it for yeast starters.

 

[dead not sleeping]

Yes, Teflon, PTFE.

You are using the variable resistor (rheostat) as a current limiting device. The voltage remains the same at the motor. The energy restricted by the resistor will be released as heat across the resistor. After a while, that heat will degrade the resistor. As long as the wattage rating of that resistor ( from the photo, looks like a 1/2 watt ) is larger than the power used ( motor + heat ) you will be OK.

A better way to regulate DC motor speed would be with Pulse Width Modulation, or PWM. PWM units can be had on Ebay on the cheap ~4-5 bucks, not much more than you paid for the VR. Simple hookup, power in and power out. It works by turning on and off very fast in variable ratios. This produces an average voltage over time, thus slowing the motor down. The motor can't figure that out and it doesn't care. Silly motor. You should be OK with your setup though so enjoy !!! If it does not work out, that's your issue. Congrats on your DIY. Its great to build something and have it work out.

Edit: if that resistor or your wall wart gets overly hot, you will need to go with PWM. Can't see that happening with that bitty little fan motor though. It doesn't draw much of any kind of current.

 

[CajunCloud]

Nice job. I'll be building one myself soon. Thinking I would use a a dying fan that barely spins keep the speed down. Just kidding I will have to get a rheostat as well and wire it all up. Not a big deal. I was going to say usually for parts like this you can't hook them up wrong it will just function opposite of intended Like swapping wire on an electric motor changing its direction. But some parts can let out the magic smoke so be careful all you DIY guys if you get into fancier setups.

IMO stir plates are a must have if you want to know ASAP how it will taste when mixed. I'm not interested in waiting weeks to get a final profile to determine long term taste for a 120ml mix of it.

CC

 

[froginblender]

what u need help with cajun...im drinking bourgon..and beerrrr now...............................................who needs the more attentiton..??? lmao.

 

[froginblender]

Nice job. I'll be building one myself soon. Thinking I would use a a dying fan that barely spins keep the speed down. Just kidding I will have to get a rheostat as well and wire it all up. Not a big deal. I was going to say usually for parts like this you can't hook them up wrong it will just function opposite of intended Like swapping wire on an electric motor changing its direction. But some parts can let out the magic smoke so be careful all you DIY guys if you get into fancier setups.

IMO stir plates are a must have if you want to know ASAP how it will taste when mixed. I'm not interested in waiting weeks to get a final profile to determine long term taste for a 120ml mix of it.

CC

didn't i link a hypertext linke for ou on ebaby>????

 

[CajunCloud]

I think I'm good on this one FNB lol. Just need the pieces parts to make it happen. But then again I might just ebay me one and call it a day. Just moved so my workshop for DIY is in boxes. I'd like one with heat if I can get a good price. I posted one I should have gotten the other day here. 5 spin pads on one unit. Sweet!

CC

PS Go easy on the Booze mixing them. That is a DIY recipe for disaster

 

[froginblender]

I think I'm good on this one FNB lol. Just need the pieces parts to make it happen. But then again I might just ebay me one and call it a day. Just moved so my workshop for DIY is in boxes. I'd like one with heat if I can get a good price. I posted one I should have gotten the other day here. 5 spin pads on one unit. Sweet!

CC

PS Go easy on the Booze mixing them. That is a DIY recipe for disaster

Sounds great Cajun, send pics when it's done ok.

 

[krwynn]

....removed

 

[Noflers]

Ran into a slight problem. When I was running my stir plate with just water it does just fine. Today I mixed up a n 85VG/15PG to use as a base and the stir bar barely chugs around in my beaker because the mix is too thick.... What's going wrong?

 

[froginblender]

Ran into a slight problem. When I was running my stir plate with just water it does just fine. Today I mixed up a n 85VG/15PG to use as a base and the stir bar barely chugs around in my beaker because the mix is too thick.... What's going wrong?

Well the VG is too thick for it.
I would put into hot water bath in sink for about 3 or 4 minutes, that will fix problem.
Or microwave for (depending on amount , volume ) and hit that for like 5-10 seconds.

That will loosen up the vg so it will stir.
or use less vg say 60/40 vg/pg

 

[Noflers]

That still leaves the issue of the liquid cooling down over time, thus bogging the motor down...

 

[froginblender]

Well that's how i do it, and i can vape my stuff str8t away.

I did make a video of my mixing, i usually do 40/60 pg / vg.

And you'll notice it spinning rapidly......i did heat it in sink for 4 min. in hot water first.
check it out:



p.s

or buy stir plate with hot plate too...it will cost you over $100 tho.........
http://www.amazon.com/s/ref=nb_sb_n...s=aps&field-keywords=stir+plate+with+hotplate

 

[krwynn]

Ran into a slight problem. When I was running my stir plate with just water it does just fine. Today I mixed up a n 85VG/15PG to use as a base and the stir bar barely chugs around in my beaker because the mix is too thick.... What's going wrong?

Use a bigger stir bar. At least 1" long. That way the magnetic has more area to work.