Help with my stir plate

Hi all,

I used the thread here called cheap and easy stirplate. I followed the tutorial exactly but for some reason I can't get things right for the stir bar to spin in my container. If I just sit the stir bar on top of the plate and turn it on, it will spin. I can't figure what i amdoing wrong. The bar just seems to rattle in the flask. Can someone give me some help?

TIA,

m

The bottom of your vessel might not be flat enough. You might try starting the thing out slowly, then increasing the speed. Sometimes the bar will spin so fast, it will fly off. That's more of a problem of balance than anything though.

I'd check out the vessel and see if it's flat. Maybe try another one.

I tried a couple different containers before I found one with a perfectly flat bottom. Once I got that set up it works great but I do have to slowly ramp up the speed of the stirbar or it will fly off the axis.

Proximity of the stir bar to the magnets and length of the stir bar will have a large effect on a home-made stir plate. If you use a smaller stir bar, it will spin easier. If the stir bar is too long, it won't spin. If your magnets are weak, you need to get the stir bar pretty close to the magnets.

you really just gotta play around with the distance your stir bar is from the magnet and where on the fan the magnet is.

Also mess around with the speed of when you first turn it on. I built one from that thread for myself and it kicks the bar unless I start at full speed.
Then I built one for a friend and it kicks the bar unless you start it at the slowest speed. (more common from what I have read)

Thanks for the replies. I did try several containers thinking the same thing about the flat bottom. I have several different sizes of stir bar as well. The thread here only showed using on of the hard drive magnets, should I try both? I made sure I started at the slowest setting but no joy.

I put my stirbar in a cereal bowl and manually raised or lowered the bowl over the striplate untill I got action I liked. I still couldn't get it to spin though. Then I added two of the dip tube o-rings to my homemade stirbar and off she went.

You made the stirbar? What did you use ?

Lupy said:

Then I added two of the dip tube o-rings to my homemade stirbar and off she went.

Click to expand...

I'm not sure I follow.

springer said:

You made the stirbar? What did you use ?

Click to expand...

Not the bars... The plate

When i was building the plate all I had was some of these magnets 8mm x 1mm
They allowed me to determine the right length of bar to use. They appear to rust so i have not used them in a starter yet. I am thinking about coating the 'bar' with food grade silicone.

The o-rings just go on the bar about 1/3rd of the way from each end. I can't get a pic to load on this 'puter but I'll try again later if someone hasn't beat me to it.

ETA:

springer said:

You made the stirbar? What did you use ?

Click to expand...

I did make one that worked pretty well, but not as well as the plastic-coated ones from Northern Brewer.

I took a 1" steel rollpin and superglued a very small plastic washer at its midpoint. Spun like a top. FYI, I have a single HD magnet in my stirplate.

I asked because commercial stirbars are magnetic and therefore enhance the magnets on the fan. If He was useing a homemade one like yours then that could have been the problem ,not enough magnetic attraction.

springer said:

I asked because commercial stirbars are magnetic and therefore enhance the magnets on the fan. If He was useing a homemade one like yours then that could have been the problem ,not enough magnetic attraction.

Click to expand...

Yep. My non-magnetic one worked fine with water, but add some DME and yeast in there and the bar would eventually spit to the side of the flask.

I have made sure I have a flat bottom in my container....I swear I have tried all size of my bars, moving it around...i cant get the darn thing to spin inside a container! this stir plate is driving me stir crazy!

EDIT: Is it possible that my magnets just arent strong enough to spin the bar through a container?

What voltage is your wall wort? When I first built mine it did the same thing. I found that if i pulsed it with the rocker switch on a power strip I could get it to spin really well. This leads me to believe the 9 volt power supply is spinning the fan to fast. I'm going to try a 5 volt supply before I go to the LM317 design. Also, the real stirbar makes a big differance as it is magnetic also.

The LM317 is the best way to get stir plate working with any flask. If you really don't want to do that, try going down to about 3.3V. That voltage worked fine for me all the time until I just added the linear regulator and pot.

It's not that I'm too lazy to do the LM317 circuit, I'm just new to electronic circuits. I will eventually go with that design, though.

hmmm....may have something with the voltage there. I have noticed when it first starts it does spin, so maybe the slowest speed is still too fast. I am pretty sure I used a 9v power supply.

If your stir bar will spin on the plate by itself buy not in a flask with water, it's probably because the drive magnets aren't close enough to the stir bar. Try putting some spacers or washers under the computer fan to get that HDD magnet as close to the top of the stir plate box as possible. You didn't mention what type of container you are using, but an erlenmeyer flask will get your stir bar closer to the drive magnet than, say a growler or other type of jar. The glass on the bottom is thinner.

hey all....you were pretty spot on with my voltage. I was actually using a 12v power supply...yikes. I switched it out with a 5v power supply and I did get my 1" stir bar to spin in a jar. soooo....apparently, it was the voltage. but i will say this...the "flask" i had intended to used, I etched it and everything...it has a convex bottom, soooo I guess I will be ordering a real Erlenmeyer.

SS - You also may have something, as I have plastic spacers separating the fan from the enclosure like the OP of the stir plate thread had done. maybe I should get shorter ones.

Thanks all

ok...so one more thing. haha....after I took SS's advice, I stacked my two magnets from the HDD instead having one. Well the bars spin much easier now! I think...its almost too slow though. I get a small vortex with a small amount of water in a small container. What will happen with a more viscous liquid in a larger container??....think I need to put my 12v back on?!

a little lookie at what I see...

rhltechie said:

...think I need to put my 12v back on?!

Click to expand...

Yes. This morning I added 2 more magnets to mine (3 now) and I can run my plate at full 12V. That is in water, but it is a good sign. I'm pulling a nice vortex down a 4000ml erlenmeyer (filled).

I used a Radio Shak variable voltage power supply 1.5v - 12v.
It sure made the project easier and I'm not sure i would have been successful without it.

well i put the 12v back on...no go. still too fast. so I had a 9v sitting around too, still no go. apparently the sweet spot is between 5 and 9!

Lupy, I wish I had done so. I may still....it's working but its not got much of a vortex going. just not sure how much is needed to make this a productive project.

rhltechie said:

well i put the 12v back on...no go. still too fast. so I had a 9v sitting around too, still no go. apparently the sweet spot is between 5 and 9!

Lupy, I wish I had done so. I may still....it's working but its not got much of a vortex going. just not sure how much is needed to make this a productive project.

Click to expand...

Maybe you should consider this:
http://www.brewershardware.com/kits.htm
Requires you to solder.

Mine works with either 12 V or 9volt in fact I can switch between the two if I want with a quick disconnect. But I have two strong ass magnets that I order online from K&J Magnets I think they were like 10 lbs of pull force.


this is with the 12v only makes the noise when I have water in it . I guess the worts viscosity stops the noise