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Blue Helix
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How to make a _good_ magnetic stirrer for cheap 4
#26877787 - 08/13/20 01:24 AM (3 years, 5 months ago) |
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First, why would anyone even want a magnetic stirrer? If you don't have this and use the "swish daily" technique, the LC develops a lot less robustly. It's slower to develop and looks like snot rather than blobs. With a magnet stirrer you LCs will explode in the jar and look more like these:
 
Given the ridiculous price of magnetic stirrers for a lab I can certainly see why people seldom buy them. though. Of course, eBay has the cheapies direct from China, but I've tried them and they have a fatal flaw: they are using a PC fan motor with a resistor for speed control. That means they spin too fast on all settings.
The lowest I could dial mine down before it stopped was maybe 700 RPM. And even at that speed, the motor won't last long because it's not designed to do this! In other words, they are junk not worth $5, much less their $40 to $60 price tag! That's kind of expensive for a device that moves a magnet in a circle even if it did work right (which it doesn't).
What I'd like to do is go through the steps of making good one for about $20 or less (depends on how much stuff you have). First, let's list the parts, staring with the most expensive component ($14), the beautifully-built geared-down motor:
- 300 RPM @ 24V DC Gearhead motor from Amazon - we'll be using this gearhead motor to spin 150 to 200 RPM by using 9V to 12V. That's about the speed you want, not 300 RPM at 24V and definitely not 1000 RPM like PC fans and the junk ones on eBay. This is such a beautiful little motor I felt kind of bad just using it for this humble task since it can handle a lot of torque, but it has the right speed.
- A half-pint wide-mouth jar with 2 plastic lids. You should be using those to make my LC lids as I described here
- Narrow-mouth Kerr lid. This is kind of optional because if you think about it, almost anything could work, even and inch and a half of a Popsicle stick with a hole drilled in the middle for the shaft. I liked the narrom-mouth Kerr lid because the magnets stick to it without glue.
- Drill with some common-sized bits (you can sort of use whatever sizes are close to what you want) - can be hand drill or whatever
- Hot-glue gun
- Some duct or gaffers tape
- DC power box for either 9V to 12V DC is best. Don't worry about how much power the box can produce because I measured 2 watts at 9V (basically nothing). Here are two examples, but I'm sure you can either find one in some junk around your place (or a thrift store) or buy them even cheaper. -
eBay direct from China for less than $2 Through Amazon for $7
- Two small magnets. Neodymium is better but whatever would probably work (the dime is there for size comparison purpose only)

- Optional: Teflon stir bar. It's not shown here but I also stretch a piece of silicone rubber in the middle so it doesn't clink with the glass when spinning. Stir bars can be anything that can hold up in a pressure cooker, is between say 3/4" and 2 1/2" long, and is attracted to a magnet (use your imagination).
 Okay, so instead of write a lot of boring words, I am going to show you pictures and animations of mine already done, both fully assembled and apart.
First here is the unit fully assembled, the two lids (the full one and the one that has the shaft through it taped with duct tape) and running at the right speed for mixing an LC, which is around 100 RPM at 9V as shown. Notice how the magnet sweeps across the bottom rather than rotate in the middle? That's because of how I have my magnets inside, but I liked it that way because it does a better job of mixing the entire jar. I took the sound out, but its almost totally silent at 12V or less (I'd guess around 10db TOPS):

Now let's remove the tape, remove the top full plastic lid, and take a look inside. Notice the magnets on the half-pint narrow mouth lid? Those were not even glued because there was no need. You must make them opposite poles facing up. If you don't know what that mean, get out your Teflon magnet and make sure it sticks to them. Notice how the shaft had a dab of hot glue on it. :

And spinning (note: this doesn't have to spin perfectly. Just make it as good as you reasonably can):

And in the half-pint jar is the motor which had a dab of hot glue on top to make it stick to the lid. I had to bend the metal power tabs sideways for it to fit in the half-pint jar with the lid on. Also while one of those holes was in the lid to run the cord, the other was because I used a junk lid that I practiced making holes in since you cannot see it anyway:

And what about that power supply? Well anything from about 9V to 15V DC is fine. The motor and the DC power supply I used took only 2 watts at 9V according to my tester, which means it's like less than $2 to run the entire year if you did that. Most of that is simply a typical vampire load, though, so if you don't want that, buy the weakest power supply you can find :

Well, that's it! It's not adjustable, but if that is a big deal to you, get a variable voltage power supply. The motor can handle up to 24V which would turn it a bit too fast at 300 RPM, so I'd stick with 12V to 6V (lowest) for a good mycelium-growth RPM.
Edited by Blue Helix (08/14/20 12:08 AM)
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jcm4620
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix]
#26877848 - 08/13/20 03:33 AM (3 years, 5 months ago) |
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sweet if i ever go the lc route il be makin one
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: jcm4620]
#26877854 - 08/13/20 03:49 AM (3 years, 5 months ago) |
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Quote:
jcm4620 said: sweet if i ever go the lc route il be makin one
Yeah that motor I just got today because I wanted to make sure it would work (I had some weaker, more noisy ones). Well, the motor is way too good for this task, but hey, it was only $14 I guess.
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lovepotion
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix]
#26877868 - 08/13/20 04:23 AM (3 years, 5 months ago) |
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He's back! This looks 1000x more legit than the computer fan plates that are stopped with fingers
I like how you incorporate hot glue into your teks. A signature perhaps. Hot Blue Gun
-------------------- Staying Out to Lunch
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: lovepotion]
#26878735 - 08/13/20 02:38 PM (3 years, 5 months ago) |
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Quote:
lovepotion said: He's back! This looks 1000x more legit than the computer fan plates that are stopped with fingers
I like how you incorporate hot glue into your teks. A signature perhaps. Hot Blue Gun
The reason I use hot glue in small projects like this is because hot glue sticks to both metal and plastic well, isn't permanent, and still hardens fast. Those properties are what make it so valuable. When I was making this yesterday, I thought about some things that might go wrong (like say the glue dribbled down onto the motor's shaft and seized it) and, instead of using epoxy, I used hot glue just in case I had to backtrack. Of course, any place I used hot glue, you can probably use epoxy putty or epoxy glue--I have both--but if I want to use that motor later for say a multiple spinner version, then it might be super hard to remove the epoxy. I like to keep my options open for future projects.
Edited by Blue Helix (08/13/20 02:44 PM)
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verum subsequentis
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix] 1
#26878756 - 08/13/20 02:48 PM (3 years, 5 months ago) |
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What do you have against higher rpm? I personally love to spin the ever living shit out of the LC. I prefer thousands of tiny myc fragments to hundreds of little blobs. I find it spreads through the grain bag better without getting caught up in certain areas. Not that it makes a world of difference though.
Nice write up.
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Blue Helix
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Quote:
verum subsequentis said: What do you have against higher rpm? I personally love to spin the ever living shit out of the LC. I prefer thousands of tiny myc fragments to hundreds of little blobs. I find it spreads through the grain bag better without getting caught up in certain areas. Not that it makes a world of difference though.
Nice write up.
Good, question, and it's one that I wondered too since making a "spin the shit out of it" mag stirrer is trivial with a PC fan and two magnets. So why bother with slower (traditional lab) spin speed?
Well, if you stir the shit out of it--and I used to do that so I'm not knocking it here--all that happens is that you cannot tell mold contamination very well (you can still see bacterial though since that's just an LC that doesn't settle and is cloudy). I hear people bitching and moaning that they cannot spot contamination all the time with LCs. In fact, it's one of the reasons people won't try LCs even. I don't have that problem at all. The reason the myth exists that one cannot spot contamination is because they aren't spinning it at the right speed (usually way too fast) or at all (the swishing disaster).
But, still, if you like super fast RPMs and want to save about $7 or so, just glue two magnets on the blades of a PC fan (online they run all of $4 or so), get a box power supply around 9V, and sit the jar on the fan guard. That's what I used to do at least, until I realized you cannot spot simple contamination like that very well.
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Blue Helix
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Quote:
verum subsequentis said: What do you have against higher rpm? I personally love to spin the ever living shit out of the LC. I prefer thousands of tiny myc fragments to hundreds of little blobs. I find it spreads through the grain bag better without getting caught up in certain areas. Not that it makes a world of difference though.
Nice write up.
Adding a little more here: if you spin around 150 RPM, you can even tell the type of mycelium growing in there in terms of rhizomorphic, linear, etc. by looking carefully at the blobs. Spiky bigger blobs, for example, are a sign of rapid rhizomorpic grow. Again if you are swishing or spinning it crazy fast, you can't do that.
Also, if you are using the LC lids I describe, you can always give it a hearty shake right before the draw if you really think it helps it spread better. I have serious doubts about that, though.
Edited by Blue Helix (08/13/20 04:47 PM)
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greenmachine78
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix]
#26878885 - 08/13/20 04:33 PM (3 years, 5 months ago) |
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Find a microwave on the side of the road it moves a little slower and is easy to just plug in. I use them for all sorts of things.
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: greenmachine78]
#26878919 - 08/13/20 04:52 PM (3 years, 5 months ago) |
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Quote:
greenmachine78 said: Find a microwave on the side of the road it moves a little slower and is easy to just plug in. I use them for all sorts of things.
Yeah, I guess you can use a microwave or maybe even a motorcycle idling. Lots of things spin slowly but might not be totally practical. If you'd like this thing to spin slower, that part is super easy. Just get a more geared down motor on Amazon. Instead of 300 PRM at 24V, buy the 100 RPM at 24V and run it on 6V. Or buy the 110V AC version at the exact speed you want and just plug it into the wall. They have motors that go as slowly as you want for about the same price basically.
The speed I recommend is based on my own experiences with a real lab-grade unit that could adjust from 1 RPM to 1000 RPM. I got the used unit for about $40 and it worked for about a decade. Eventually it started to disregulate and spin at random speeds, including stopping for several minutes sometimes. It's kind of worthless now because it'll jerk really fast and the magnet cannot keep up. That ends up making all sorts of noise, and I hate noise.
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coAsTal
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix]
#26879190 - 08/13/20 08:15 PM (3 years, 5 months ago) |
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I like it-- I already have everything but the motor, so I'll let you know when it arrives and I get it built up-- thanks so much for the great DIY TEK.
-------------------- I am certain of nothing but the holiness of the Heart's affections and the truth of Imagination-- John Keats Spore Trading List
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: coAsTal]
#26879338 - 08/13/20 10:39 PM (3 years, 5 months ago) |
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Quote:
coAsTal said: I like it-- I already have everything but the motor, so I'll let you know when it arrives and I get it built up-- thanks so much for the great DIY TEK.
That motor came within 24 hours to me. It's just a beautiful motor too. I wasn't expecting something as nice as it is. I even opened the gear cage just to check it out, and it looks top notch.
One thing I don't talk enough about is running the cord. I ran mine out of between the two lids. It is normal for the two lids to have a 1/16" between them because the motor's shaft is just a tad too long to fit between them. That let's you run the cord out in the gap, and you can tape both the lids with that tiny gap. It's not a big deal. I'm just telling you so you don't think you did something wrong.
Also the motor is tight in the half-pint. Like I said, I had to bend the terminals sideways to get it to close well.
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Bsdgaou

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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix]
#26879347 - 08/13/20 10:48 PM (3 years, 5 months ago) |
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Magnetic coffee stirer is 12€ brand new. Just saying...
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Bsdgaou]
#26879371 - 08/13/20 11:07 PM (3 years, 5 months ago) |
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Quote:
Bsdgaou said: Magnetic coffee stirer is 12€ brand new. Just saying...
Like I keep saying: I can make you a fast LC stirrer for about $5 using a PC fan ($3), two magnets (25 cents), and a power box ($2). I don't want to because in the title I said "_good_", but that would be shitty. Those gears in the motor are expensive. That's because they don't sell 100,000,000 of them a year like coffee stirrers. Just saying...
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coAsTal
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix]
#26879717 - 08/14/20 08:00 AM (3 years, 5 months ago) |
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Yeah, I toyed with the idea of the PC fan variants-- but I don't want shitty plastic fans running that fast, and the added weights to the fan blades would be far more than they're designed to safely spin. (If I wanted to try that I could have done it with parts I already have.)
It's the small rock-solid little motor that's the key to making it a great DIY- - because it's perfect for this function. I'll post an update once I build mine, so other people can see how easy it is.
BH, you should consider linking this together with your LC reasoning/method post/journal(!), because once people see how you can safely get away from needing SAB/Flow hoods to nock up spawn bags with these things, it all comes together on how great a fit the methods are for a smooth operation--especially for people like me that have extremely limited space for their hobby.
Once I get this spinner built, I'm going to have to decide what type of mushroom I want to try an LC on first.
-------------------- I am certain of nothing but the holiness of the Heart's affections and the truth of Imagination-- John Keats Spore Trading List
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: coAsTal]
#26882327 - 08/15/20 08:27 PM (3 years, 5 months ago) |
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Quote:
coAsTal said: Yeah, I toyed with the idea of the PC fan variants-- but I don't want shitty plastic fans running that fast, and the added weights to the fan blades would be far more than they're designed to safely spin. (If I wanted to try that I could have done it with parts I already have.)
It's the small rock-solid little motor that's the key to making it a great DIY- - because it's perfect for this function. I'll post an update once I build mine, so other people can see how easy it is.
BH, you should consider linking this together with your LC reasoning/method post/journal(!), because once people see how you can safely get away from needing SAB/Flow hoods to nock up spawn bags with these things, it all comes together on how great a fit the methods are for a smooth operation--especially for people like me that have extremely limited space for their hobby.
Once I get this spinner built, I'm going to have to decide what type of mushroom I want to try an LC on first.
Yeah. If you have any questions about ANYTHING LC-related, let me know. I actually happened to have the M3 screws for the top of this motor, but it's just so easy to make it hot glued that I didn't use them.
PS - I also linked this to my LC lid-making post as you suggested.
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Hobbit GDF
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix]
#26882336 - 08/15/20 08:33 PM (3 years, 5 months ago) |
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Very cool. This is how my homemade one looks. Works so fricking good too. Just sit the media bottles on top the lid. I love this stir plate. Why are real ones expensive?
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Hobbit GDF
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Re: How to make a _good_ magnetic stirrer for cheap [Re: lovepotion]
#26882344 - 08/15/20 08:41 PM (3 years, 5 months ago) |
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Quote:
lovepotion said: He's back! This looks 1000x more legit than the computer fan plates that are stopped with fingers
I like how you incorporate hot glue into your teks. A signature perhaps. Hot Blue Gun
Why are PC fans not good? I can stop it with my finger. But I have a lid and never need to touch it. Its strong and stirs very well
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Hobbit GDF]
#26882422 - 08/15/20 09:39 PM (3 years, 5 months ago) |
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Quote:
Hobbit GDF said:
Quote:
lovepotion said: He's back! This looks 1000x more legit than the computer fan plates that are stopped with fingers
I like how you incorporate hot glue into your teks. A signature perhaps. Hot Blue Gun
Why are PC fans not good? I can stop it with my finger. But I have a lid and never need to touch it. Its strong and stirs very well
This is the last time I cover this again: a PC fan does not operate nearly slow enough to be optimal. I played around for many years an expensive lab stirrer that could go from 0 to 1000 with the turn of a knob. I found that anything higher than about 200 RPM just blended the whole LC so there was no character left in it to see contamination. It just became a mess of snot basically. At that RPM, mold looked just like a good LC. So if that doesn't bother you, you can make a PC-fan based one for about $5 or less. Regretfully, I used them for some years myself, and I wasted time using them too because they just were basically a blender with no way to see the mycelium characteristics as it grew. It's kind of like if someone took their agar plate each day and ran it through a meat grinder. I guess if the plate was clean, it wouldn't matter.
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Blue Helix
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Re: How to make a _good_ magnetic stirrer for cheap [Re: Blue Helix] 1
#26890011 - 08/20/20 12:31 PM (3 years, 5 months ago) |
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I just wanted to emphasize my point about why lower RPM LCs matter. Below is an animation of a lower RPM LC. It's the motor in this thread being run at 9 volts, one of the recommended voltages. Notice how the balls are not smashed up and do not form a cloudy slurry as they would with a typical PC-fan-based stirrer. I've seen enough agar plates to practically know what this would look like on agar, and it's not contamination. Contamination would be if this was like heavy snot flying around, but unfortunately, with a PC-fan-based stirrer or with the daily swishing technique, it'd look like that too. The easiest way to tell if a LC is developing right, is to slow down the stirring to under 150RPM or so. In this case, 5V would probably be even better, but this is fine too. My final question is this: isn't that information worth around $10 or $15 extra to you? It is for me. If at the end you want to wreck the structure up, you can just shake it hard (although these balls are not strong enough to jam a syringe typically).
PS - Also, note there is a tiny bit of cloudiness. That's fine as long as it doesn't get more cloudy. This is typical of LCs that might have a very minor degree of bacteria in them early on or for some types of dry malt extract that just happen to have solids until the mycelium pulls it out. In 48 hours that would totally go away here.
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