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

twd000 said:

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How do you have your magnets arranged?

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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.

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.

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?

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.

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?

twd000 said:

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?

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

mightynintendo said:

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

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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

twd000 said:

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

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

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?

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.

Jukas said:

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?

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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.

twd000 said:

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?

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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.

Jukas said:

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.

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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.

camiller said:

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.

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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.

subscribed stirplate 987

camiller said:

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.

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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.

twd000 said:

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.

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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.

twd000 said:

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.

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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?

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

barrooze said:

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?

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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?

twd000 said:

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?

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I just adjusted by feel until there was no wobble, then cemented down. I have made a few dozen starters since then, and the fan has not burned out yet. Knock on wood.

twd000 said:

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?

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How I did it:

1. Start the fan spinning
2. touch a sharpie as near as possible to the center, making a circle slightly smaller than the hole in the fender washer
3. stop the fan and use the spot to line up the washer and glue in place
4. draw a line across the washer and place the magnet(s)
5. put the stir bar directly on the magnets and turn on the fan.
6. viewed from above the center of the stir bar should look like a solid circle the width of the stir bar while the remainder has a kind of blurred appearance. If not adjust accordingly.
7. once it looks centered while spinning, mark the location of the magnets on the washer and remove/glue/replace.

Thanks to this post I was able to figure out a few problems I was having with my Stirplate.
First, I couldn't regulate the speed with my potentiometer. I wired it differently using directions from a Utube video.
Second, I kept throwing my magnet. I felt it was due to not being able to regulate the speed of the fan but it was also that I had to many volts powering my fan. I had a 12 volt power supply. When I switched it to a 6 volt it was a perfect combo of speed and power to keep the magnet centered.

Thanks everyone... I love this hobby!

My stirplate Ver. 2.0 passed it's 24 hour QA test. Thanks for all the help. Pete

Old heatsink fan √
Old hard drive magnet √
Some artsy fartsy box my wife is probably going to kill me for drilling holes in even though it only cost $2 √
A stirbar from ebay √
Lots of good info from this thread √

just got everything to make one of these next week, only thing is that the power switch only has two post on the back of it?

Works like a charm, only think I did different was I bought a fan at Radio Shack and the total bill was still around 32 dollars. The fan I bought was so tight that I had to remove the “ripped” material from inside the box, small sharper chisel, and it came right out. I went to a smaller hardware store and bought bolts that just made it into the holes, and then they “tapped” in with a driver and holds it at perfect height.

That's a Rheostat and power switch in the background. My only regret is that I put the switch in the center of the box instead of moving it to the left to balance out the look of the front of the stirplate. OH well...


I put in a plug for the "wall wart". It looks nice and neat and allowed me to brush up on the soldering skills.


The height of the fan is adjustable. If I find the pull on the maginets is too much I can lower the fan.


2 Neodymium Magnets 3/4 x 1/4 off ebay. These things are insanely strong!



My total cost was about $30. I'm happy with it. It was fun to build and works like a charm! Beats the hell out of buying one for 100.00

i gotta do this

good11s said:

i gotta do this

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Yes you do. It's a fun and easy project to do. And best of all it saves you a ton over what you can buy elsewhere ready made.

EllisTX said:

Old heatsink fan √
Old hard drive magnet √
Some artsy fartsy box my wife is probably going to kill me for drilling holes in even though it only cost $2 √
A stirbar from ebay √
Lots of good info from this thread √

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Square root?

petey_c said:

Square root?

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Damn it. I knew someone was going to catch that.

I'm looking to build one of these so does anyone know a cheap place to my the flasks? They seem a bit pricey at the homebrew stores.

Diver165 said:

Yes you do. It's a fun and easy project to do. And best of all it saves you a ton over what you can buy elsewhere ready made.

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It is that easy too, just follow the OP and everything goes together that easy. That coming for some that knows nothing about wiring anything. At the cost of 1/2 to 1/3 the price of a pre-made one, I might make two of them.

Cheers

cincybrewer said:

I'm looking to build one of these so does anyone know a cheap place to my the flasks? They seem a bit pricey at the homebrew stores.

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brewmasterswarehouse has 2L ones for 19.99 and 6.99 flat rate shipping. That's about as cheap as I've found them for the 2L version

Check out Cynmar. Pretty good prices. Found the flasks when I was looking for yeast slanting stuff.

My ghetto stir plate with my first starter in a Pyrex decanter I got at goodwill for $0.99

JonGrafto said:

My ghetto stir plate with my first starter in a Pyrex decanter I got at goodwill for $0.99

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What size flask is that and what volume starter are you stirring?

barrooze said:

What size flask is that and what volume starter are you stirring?

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It's about a 2L glass. I split my smack pack on half and I am building it up. What's in there is about a liter

www.homebrewstuff.com has stir plates for $42. Based on cost of the parts for the DIY and the value of my time that is a damn good price!!!