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

[aubiecat]

What you are seeing is the pocket that is milled into the bottom of the poly base but it doesn't go all the way through. It's milled out to allow for the part that holds the magnets.

 

[DoctorMemory]

It is overkill but fun to do

You can never have too much overkill!

 

[Siczek]

Ok, got my washer glued and tested out agitation using the other hard drive magnet and success! The thermaltake fan is excellent. Tomorrow during my Maibock brew I'll be mounting into my box and should be going into final assembly. Will post pics when done.

 

[Gear101]

nice build plans on making one this weekend

 

[aubiecat]

Ok, got my washer glued and tested out agitation using the other hard drive magnet and success! The thermaltake fan is excellent. Tomorrow during my Maibock brew I'll be mounting into my box and should be going into final assembly. Will post pics when done.

I used a 120mm Thermaltake for mine. It came out of an older computer that was running for years. I expect it to run on my stirplate for many more.

 

[twd000]

I've got my electrical circuit up and running. Trial-and-erroring with the magnets. I've got some neodymium disc magnets, and the 50-mm stir bar with center ring from Northern Brewer. I have tried taping on one or two disc magnets on the center hub of the fan, with no luck. It's almost like the fan is spinning too fast, even with the rheostat at the lowest setting. What RPM do you estimate you're running at? Like slow enough to count the blades?

If I hold a magnet on its edge and spin it under the flask, it rotates the stir bar. But it doesn't "see" the field when attached to the spinning fan hub.

 

[coypoo]

I've got my electrical circuit up and running. Trial-and-erroring with the magnets. I've got some neodymium disc magnets, and the 50-mm stir bar with center ring from Northern Brewer. I have tried taping on one or two disc magnets on the center hub of the fan, with no luck. It's almost like the fan is spinning too fast, even with the rheostat at the lowest setting. What RPM do you estimate you're running at? Like slow enough to count the blades?

If I hold a magnet on its edge and spin it under the flask, it rotates the stir bar. But it doesn't "see" the field when attached to the spinning fan hub.

How much power do you have coming into the fan? Have you tried it with any resistance?

I thought my 9V wall wart was too much juice, but when I switched to a 5V it wouldn't spin well in a real starter. The 9V works perfectly now (but I also added an additional magnet)

 

[twd000]

How much power do you have coming into the fan? Have you tried it with any resistance?

I thought my 9V wall wart was too much juice, but when I switched to a 5V it wouldn't spin well in a real starter. The 9V works perfectly now (but I also added an additional magnet)

I have a 12V wall-wart. What do you mean by "No resistance"? No electrical resistance from the dimmer, or no water resistance with the stir bar?

How do you have your magnets arranged?

 

[mightynintendo]

I've got my electrical circuit up and running. Trial-and-erroring with the magnets. I've got some neodymium disc magnets, and the 50-mm stir bar with center ring from Northern Brewer. I have tried taping on one or two disc magnets on the center hub of the fan, with no luck. It's almost like the fan is spinning too fast, even with the rheostat at the lowest setting. What RPM do you estimate you're running at? Like slow enough to count the blades?

If I hold a magnet on its edge and spin it under the flask, it rotates the stir bar. But it doesn't "see" the field when attached to the spinning fan hub.

Have you tried moving the fan/magnet closer to the top of the box? It sounds more like you just don't have enough magnetic pull on your stir bar. Also, are you sure your magnet is well centered?

 

[camiller]

I've got my electrical circuit up and running. Trial-and-erroring with the magnets. I've got some neodymium disc magnets, and the 50-mm stir bar with center ring from Northern Brewer. I have tried taping on one or two disc magnets on the center hub of the fan, with no luck. It's almost like the fan is spinning too fast, even with the rheostat at the lowest setting. What RPM do you estimate you're running at? Like slow enough to count the blades?

If I hold a magnet on its edge and spin it under the flask, it rotates the stir bar. But it doesn't "see" the field when attached to the spinning fan hub.

"one or two disc magnets to the center"


Are they spaced as far apart as your stir bar is long?

Are they oriented so the opposite poles are up (one is "S" up and the other "N" up)?

Have you tried testing the voltage out of the rheostat to make sure you have it hooked up right and are actually reducing the voltage?

Pictures?

 

[camiller]

...
How do you have your magnets arranged?

Look at HenryVance3's first pic in post 981 of this thread, that is how your magnets should look. He, like a lot of us, glued a largish fender washer to the hub to make it easy to mess around with magnet placement before gluing them. You don't have to do that but it is easier than messing with tape.

 

[petey_c]

I recently built a stirrer using a 120V muffin fan. I tried to cobble one together using materials I had readily available. The fan motor's normal operating speed was about 2700 rpm. I decided to use a three speed fan controller from HD. Even at the slowest speed it would throw the stir bar. I then decided to use an incandescent dimmer, even though I know they're for different types of loads. There was just about a 5° range where the motor would turn at an acceptable speed using the dimmer. It also couldn't be depended on to stay at that speed once I turned my back. So I decided to do a complete rebuild of my stirplate. I used the materials list on page one here (I used a 12 VDC wall wart and a 12 V motor) and sorta bread-boarded a test jig. (Proof of theory). The 25Ω pot didn't offer as much control of the speed as I'd wanted. I found a pot that fit the bill. I didn't check the value of the pot and can get that info a little later. I'm using a 2 quart pitcher with a relatively flat bottom. I had it stirring at a good speed for a few hours. Next time I'm brewing (this week?) I'll test drive it with actual wort.

 

[twd000]

OK, got some time to work on mine again today. I measured 8V at the lowest setting, and 12.8V at the highest setting. I am running at low speed while troubleshooting magnet configurations.

I have two neodymium disc magnets. They are super-glued to a fender washer that is temporarily taped on the center hub of the fan. The discs are oriented with one N-pole up and one S-pole up. I have a 2" stir bar with center-ring, and the outside edges of the two discs are 2" apart.

I have the stir bar in a Pyrex measuring cup full of water. When I turn on the fan and place the cup right over the magnets, the stir bar rattles around the bottom and turns slowly - probably 5-10 RPM. This is while the fan is going 100's of RPM. It's like the magnets "grab" the stir bar, then drop it, grab and release, etc.

Any help?

 

[mightynintendo]

the problem sounds like there isn't a strong enough magnetic force acting on the stir bar. maybe your magnets are too far away from the bar, maybe they're too weak, maybe they're not centered well.

 

[twd000]

I don't think I can get the magnets any closer to the stir bar. I don't even have the fan in the housing - just hovering the vessel directly above the fan and magnets. The magnets are centered well enough to prevent them from being thrown off the fan when it spins up.

The magnets I'm using are 18mm diameter by 3 mm height. What size magnets is everyone else using?

 

[mightynintendo]

I don't think I can get the magnets any closer to the stir bar. I don't even have the fan in the housing - just hovering the vessel directly above the fan and magnets. The magnets are centered well enough to prevent them from being thrown off the fan when it spins up.

The magnets I'm using are 18mm diameter by 3 mm height. What size magnets is everyone else using?

well the build calls for hard drive magnets. most people are using those or rare earth magnets.

 

[twd000]

well the build calls for hard drive magnets. most people are using those or rare earth magnets.

neodymium IS a rare-earth magnet, right? which is the same material as a hard-drive magnet. So the only difference would be the size

 

[mightynintendo]

neodymium IS a rare-earth magnet, right? which is the same material as a hard-drive magnet. So the only difference would be the size

Oh. I guess I don't know then. You are using disc-shaped and everything i've seen used is rectangular-ish.

 

[Jukas]

I'm running into a problem with the stir plate I built. I'm using a 12V DC wall wort and a 120mm Antec fan. The magnet I'm using is a circular magnet from another 120MM fan.

When I put the stir bar on the plate it spins perfectly, however when I add a 1L flask the stir bar gently walks to the side and then does nothing, even with the rheostat turned to maximum.

I've added pictures as I can get them of the setup. Should I try and get the magnet closer? Try a different wall wort, or a different magnet?

 

[Accidic]

Second the magnets aren't strong enough for the build throwing stir bars. Mine wlll do 5700rpm constantly without throwing the bar on a flat surface container.

 

[Accidic]

I'm running into a problem with the stir plate I built. I'm using a 12V DC wall wort and a 120mm Antec fan. The magnet I'm using is a circular magnet from another 120MM fan.

When I put the stir bar on the plate it spins perfectly, however when I add a 1L flask the stir bar gently walks to the side and then does nothing, even with the rheostat turned to maximum.

I've added pictures as I can get them of the setup. Should I try and get the magnet closer? Try a different wall wort, or a different magnet?

Can you see the fan turning when it starts "walking" or is that possible with your setup. An empty puts little pressure on a motor but a with water it might not have the oomph to turn it. For me I use 1/4" hole 3" dia washers as both a mounting plate as well as motor shielding. This may help if it's not turning cause of the magnets. If not it may just need a push start so to speak. Alternatively you can get this problem if your voltage is too low as well.

Alternatively, re: the gap size, stronger magnets will allow a bigger gap. Mine hold fine to a little over half an inch gap. Material of your enclosure can reduce your gap. Alternatively you can stack magnets to strengthen your field to some degree. This had been pointed out before but not sure if it's been stated in a while.

 

[camiller]

OK, got some time to work on mine again today. I measured 8V at the lowest setting, and 12.8V at the highest setting. I am running at low speed while troubleshooting magnet configurations.

I have two neodymium disc magnets. They are super-glued to a fender washer that is temporarily taped on the center hub of the fan. The discs are oriented with one N-pole up and one S-pole up. I have a 2" stir bar with center-ring, and the outside edges of the two discs are 2" apart.

I have the stir bar in a Pyrex measuring cup full of water. When I turn on the fan and place the cup right over the magnets, the stir bar rattles around the bottom and turns slowly - probably 5-10 RPM. This is while the fan is going 100's of RPM. It's like the magnets "grab" the stir bar, then drop it, grab and release, etc.

Any help?

Is the bottom of the pyrex measuring cup flat? How thick is the bottom of the cup? Do you know the size/strength of the magnets? Do you have any more of the magnets so you could stack two on each end? Are you sure the tape is holding the magnet assembly centered?

If you are putting the pyrex cup over the fan after it is already spinning the magnet is unlikely to get coupled, you need to get the stir-bar lined up on the fans magnets while it is standing still, then turn on the juice.

 

[camiller]

I'm running into a problem with the stir plate I built. I'm using a 12V DC wall wort and a 120mm Antec fan. The magnet I'm using is a circular magnet from another 120MM fan.

Usually the rotor on a fan (assuming a brushless motor) is a little cup with a number of permanent magnets of alternating poles around the inside rim with the poles facing inward, not upward. The slight additional thickness of the beaker plus the additional viscosity of the water it probably keeping the stir bar from remaining magnetically coupled to the magnets on the fan.

 

[Jukas]

Usually the rotor on a fan (assuming a brushless motor) is a little cup with a number of permanent magnets of alternating poles around the inside rim with the poles facing inward, not upward. The slight additional thickness of the beaker plus the additional viscosity of the water it probably keeping the stir bar from remaining magnetically coupled to the magnets on the fan.

That's what I was thinking as well, so I've pulled a couple hard drive magnets that I intend to swap out and give a try. If that fails to work I'll have to put a voltage meter to the test and see what the wall wort is putting out.

 

[BOBrob]

subscribed stirplate 987

 

[twd000]

Is the bottom of the pyrex measuring cup flat? How thick is the bottom of the cup? Do you know the size/strength of the magnets? Do you have any more of the magnets so you could stack two on each end? Are you sure the tape is holding the magnet assembly centered?

If you are putting the pyrex cup over the fan after it is already spinning the magnet is unlikely to get coupled, you need to get the stir-bar lined up on the fans magnets while it is standing still, then turn on the juice.

Magnets are 18mm x 3 mm neodymium disc magnets. They are staying centered. The bottom of the pyrex cup is mildly concave. What is the best surface shape? I have a couple growlers I could use for starters.

I had some success starting with the magnets over the fan BEFORE starting. It spins the bar up for about 10 revolutions until the fan gets up to speed, at which time it throws the bar off. I'll get a couple more disc magnets to stack them and report back.

 

[camiller]

Magnets are 18mm x 3 mm neodymium disc magnets. They are staying centered. The bottom of the pyrex cup is mildly concave. What is the best surface shape? I have a couple growlers I could use for starters.

I had some success starting with the magnets over the fan BEFORE starting. It spins the bar up for about 10 revolutions until the fan gets up to speed, at which time it throws the bar off. I'll get a couple more disc magnets to stack them and report back.

Flat bottom is best. If the bottom is concave (from the perspective of the inside) then the tips of the stir bar may be dragging the glass. That is not necessarily bad, but if you are not holding the cup level you would get proportionally more drag on the side nearest the magnets on the fan, it really would be best to get some sort of enclosure just to eliminate unsteadiness in your hand from the equation.

 

[barrooze]

I had some success starting with the magnets over the fan BEFORE starting. It spins the bar up for about 10 revolutions until the fan gets up to speed, at which time it throws the bar off.

This happened to me when my magnet wasn't centered on the fan properly. The bar would start up and could even spin for an hour, but it would always kick off eventually. By centering my magnet, the bar is very stable now and won't kick off. It'll spin indefinitely now. Are you sure your pair of magnets are centered on the fan?

 

[petey_c]

Been running my revised stirplate for a little over three hours and it seems to running pretty consistently.

 

[twd000]

This happened to me when my magnet wasn't centered on the fan properly. The bar would start up and could even spin for an hour, but it would always kick off eventually. By centering my magnet, the bar is very stable now and won't kick off. It'll spin indefinitely now. Are you sure your pair of magnets are centered on the fan?

well, they're centered enough that they don't cause the fan to wobble, but I'm sure they are slightly off.

How accurately did you get yours centered and how did you do it? I have a digital micrometer and center-finding calipers. I can see the dimple at the center of the fan hub, but I assume I can't drill through there since the copper windings are inside the hub, right?