Re: Stir Plate Question. . . . .

My DIY stir plate is completed. But I cannot get my stir bar to spin inside my 2 quart Pyrex with water. The stir bar works fine when I place it directly on top of the stir plate. I have a 2" stir bar with a small round ring in the middle. The bar is inside a clear vinyl beer line because of the middle ring. Like I said it spins fine directly on the plate.
Thank you.

Stronger magnets or slower fan speed. And the ring is used as a pivot point... take it out of the beer line.

brewzofo1 said:

My DIY stir plate is completed. But I cannot get my stir bar to spin inside my 2 quart Pyrex with water. The stir bar works fine when I place it directly on top of the stir plate. I have a 2" stir bar with a small round ring in the middle. The bar is inside a clear vinyl beer line because of the middle ring. Like I said it spins fine directly on the plate.
Thank you.

Click to expand...

Why do you have the bar inside the beer line? The middle ring on the stir bar is there to help it spin. Sometimes it helps, sometimes it doesn't.

First, try it without the beer line, then try adjusting the magnets. Sometimes the height of the fan will also make a difference.

It might just take some experimentation to find out what works.

Hi

I'm not getting a real good mental image of this setup so pardon the somewhat generic reply...

1) The magnets on the fan may be to far away from the bar once the pyrex spaces the bar up off the table. Check it with an empty pyrex.

2) The magnets may not be powerful enough once water is involved.

3) The fan may be running to fast, try the slowest setting on your speed control first.

---------

now for the unlikely stuff:

4) Is the fan still running with the weight of the water filled pyrex bending everything?

5) Is the bar centered properly? It should snap into place.

6) Are the magnets on the fan far enough apart for the stir bar? Does it "flip out" in the water?

Lots of other strange possibilities, but that's plenty without really seeing what you have set up.

Bob

brewzofo1 said:

My DIY stir plate is completed. But I cannot get my stir bar to spin inside my 2 quart Pyrex with water. The stir bar works fine when I place it directly on top of the stir plate. I have a 2" stir bar with a small round ring in the middle. The bar is inside a clear vinyl beer line because of the middle ring. Like I said it spins fine directly on the plate.
Thank you.

Click to expand...

When you put the container with water (and stir bar) on the plate ... does the stir bar snap to the middle (over where the magnet is) or does it just lay on the side of the pyrex? If it doesn't snap to the middle then either your magnets aren't strong enough or you don't have them close enough to the top of the stir plate on the inside.

Take the bar out of the vinyl... this is no good. I have a couple of bars with the middle ridge and they spin just fine.

The magnets I am using are rectangle in shape. I have two side by side (lengthwise). They are 1" each for a total of 2"
The fan with magnets attached is appr. 1/4" from the top plate. Okay I took the beer line out and put back inside Pyrex to try again. It started to spin for a second then started to jump around and then nothing.

carlisle_bob said:

Hi

I'm not getting a real good mental image of this setup so pardon the somewhat generic reply...

1) The magnets on the fan may be to far away from the bar once the pyrex spaces the bar up off the table. Check it with an empty pyrex.

2) The magnets may not be powerful enough once water is involved.

3) The fan may be running to fast, try the slowest setting on your speed control first.

---------

now for the unlikely stuff:

4) Is the fan still running with the weight of the water filled pyrex bending everything?

5) Is the bar centered properly? It should snap into place.

6) Are the magnets on the fan far enough apart for the stir bar? Does it "flip out" in the water?

Lots of other strange possibilities, but that's plenty without really seeing what you have set up.

Bob

Click to expand...

#3) fan is appr 3" 12v and using a 12 volt cord.

#4) fan runs fine with weight of Pyrex/water on top.

#5) bar snaps into place.

#6) magnets are 2" in length. Bar is 2"

brewzofo1 said:

The magnets I am using are rectangle in shape. I have two side by side (lengthwise). They are 1" each for a total of 2"
The fan with magnets attached is appr. 1/4" from the top plate. Okay I took the beer line out and put back inside Pyrex to try again. It started to spin for a second then started to jump around and then nothing.

Click to expand...

Like I said, you either need more powerful (or closer) magnets, or you need to slow the fan down.

Hi

The fan needs to be running below about 750 rpm to do much good as a stir plate. Unless you have a very unusual fan, you need to add a speed control.

Bob

brewzofo1 said:

It started to spin for a second then started to jump around and then nothing.

Click to expand...

A 2" stir bar is big and going to have trouble getting started. Also, if the fan spins too fast it can throw the bar. I have this same trouble with mine, although the largest bar I have is 1.5"

Even with the Rheostat set to run my fan on the lowest setting is too fast to get it going without throwing the bar.

What I do is hold my beaker about 1/2 inch over the stir plate while the spin gets going. Once it's going I can set the beaker down and it doesn't get thrown. Sometimes it takes a couple of tries.... but I can always get it spinning this way.

I don't know about that 2" bar.... you might want to get a 1" bar. You'll likely have better luck.

One more note I should add is the stir bar is not round. It is octagon shape.

Hi

If you look at commercial stir plates, they often go down to below 100 rpm. Most normal fans run at 2,000 to 3,000 rpm. You can get <1,000 rpm fans, but they are unusual. For big stir bars, you want low rpm's. Beer / wort / yeast is harder to stir than water. You will need lower rpm's for it than for water.

Bob

I played around with the stir bars and found that 1.5" and 2" were too long for my setup. A 1" bar stirs adequate, and tends to not fly off when you increase speed. I linked one which is 1" and has no pivot ring (those things make the stirrer very loud). Round vs. octogon does not seem to really matter.

http://www.amazon.com/dp/B002VBW62Q/?tag=skimlinks_replacement-20

Having a speed control helps a lot with getting the bar under control too. It doesn't need to be too complex, just a simple voltage control. Most people just use this LM317 circuit:

ram434 said:

I played around with the stir bars and found that 1.5" and 2" were too long for my setup. A 1" bar stirs adequate, and tends to not fly off when you increase speed. I linked one which is 1" and has no pivot ring (those things make the stirrer very loud). Round vs. octogon does not seem to really matter.

http://www.amazon.com/dp/B002VBW62Q/

Having a speed control helps a lot with getting the bar under control too. It doesn't need to be too complex, just a simple voltage control. Most people just use this LM317 circuit:

Click to expand...

I put speed control in my DIY stirplate by simply using a universal AC adapter with variable voltage.

ram434 said:

I played around with the stir bars and found that 1.5" and 2" were too long for my setup. A 1" bar stirs adequate, and tends to not fly off when you increase speed. I linked one which is 1" and has no pivot ring (those things make the stirrer very loud). Round vs. octogon does not seem to really matter.

http://www.amazon.com/dp/B002VBW62Q/?tag=skimlinks_replacement-20

Having a speed control helps a lot with getting the bar under control too. It doesn't need to be too complex, just a simple voltage control. Most people just use this LM317 circuit:

Click to expand...

Hi

There's a minor error in that schematic. Some Vin greater than 28 volts isn't going to make the LM317 very happy . I'd say anything over about 15V is not useful with normal computer fans. Same issue applies to the 5k adjust pot. A 2.5K would give you better control, since you don't want to set the output to 25V. If you want to get fancy, put a 500 ohm resistor in series with a 2.0 K pot. The fan really isn't going to do very well below 3V...

Bob

carlisle_bob said:

Hi

There's a minor error in that schematic. Some Vin greater than 28 volts isn't going to make the LM317 very happy . I'd say anything over about 15V is not useful with normal computer fans. Same issue applies to the 5k adjust pot. A 2.5K would give you better control, since you don't want to set the output to 25V. If you want to get fancy, put a 500 ohm resistor in series with a 2.0 K pot. The fan really isn't going to do very well below 3V...

Bob

Click to expand...

Would work fine if you wanted an output closer to 25V

Missed that little detail, image was just pulled from the web, replaced it with one pulled from an LM317 datasheet.

I can't remember what my potentiometer resistance or my other resistor value was, but on my stir plate about half of the range of the pot results in a stopped fan. Not a big problem though.

ram434 said:

..
I can't remember what my potentiometer resistance or my other resistor value was, but on my stir plate about half of the range of the pot results in a stopped fan. Not a big problem though.

Click to expand...

Hi

Yup, the fan stalls out long before the voltage gets to zero. How low you can go depends on a lot of things, including how much dust has made it into the bearings.

There are other regulators (LT1764 is one) that will give you lower dropout voltage and get you more speed off of a 12V wall wart. For most fans, more speed is not what you are looking for....

If you want to dig into all the ugly details, Intel has some nice app notes on fan speed control.

Bob