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

mcshaw16 said:

Belay my last. I gave the fan a few spins while plugged in and it took off and it's working fine now. Still not sure what the problem was.

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The adapter may not be giving it the juice it needs to start properly. 5V is kind of low, especially since that will be the upper end of what the potentiometer will allow. But it could also be an amperage issue.

How many mA does can your adapter output? And you you have the voltage and amperage specs, and/or the make & model of the particular fan you're using?

I've searched, I've read and read (this is a long thread, and the similar thread are long). My simple stir plate is in a small cigar box, 12v fan and a 12v wall wart charger. My fan (5 inch, maybe 5.5) runs slow. The rheostat seams to have no noticable effect. My stir rod just dances. I can get it to run in a circle (not really spin) if I double-stack [two on each side-reversed poles] the batteries. (I have a small bunch of dime sized/shaped rare earth magnets form an unrelated project).
my questions:
1: Do I want the fan to spin faster?

2: Although counter-intuitive, would the fan spin faster if I LOWERED the voltage? i.e. am I better off with a 6 or 9 v charger?

As always, thanks in advance...cheers.

LabRatBrewer said:

I've searched, I've read and read (this is a long thread, and the similar thread are long). My simple stir plate is in a small cigar box, 12v fan and a 12v wall wart charger. My fan (5 inch, maybe 5.5) runs slow. The rheostat seams to have no noticable effect. My stir rod just dances. I can get it to run in a circle (not really spin) if I double-stack [two on each side-reversed poles] the batteries. (I have a small bunch of dime sized/shaped rare earth magnets form an unrelated project).
my questions:
1: Do I want the fan to spin faster?

2: Although counter-intuitive, would the fan spin faster if I LOWERED the voltage? i.e. am I better off with a 6 or 9 v charger?

As always, thanks in advance...cheers.

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I have built six of these types of stir plates. I found out two things: if the magnets are not directly in the center of the spin it will throw the stir bar and too much power too soon will throw it for sure. Lowering the total voltage into the unit allowed the stir bar to get hold of the spin and thus speed up gradually. I tried using a 13 v and then a six volt wall adapter and the 6V worked every time.

LabRatBrewer said:

I've searched, I've read and read (this is a long thread, and the similar thread are long). My simple stir plate is in a small cigar box, 12v fan and a 12v wall wart charger. My fan (5 inch, maybe 5.5) runs slow. The rheostat seams to have no noticable effect. My stir rod just dances. I can get it to run in a circle (not really spin) if I double-stack [two on each side-reversed poles] the batteries. (I have a small bunch of dime sized/shaped rare earth magnets form an unrelated project).
my questions:
1: Do I want the fan to spin faster?

2: Although counter-intuitive, would the fan spin faster if I LOWERED the voltage? i.e. am I better off with a 6 or 9 v charger?

As always, thanks in advance...cheers.

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I rink you want slower speeds, at least to start with. If you have a lower voltage power supply laying around, try it.

It also sounds like you may need stronger magnets or better positioning of the existing magnets.

emjay said:

The adapter may not be giving it the juice it needs to start properly. 5V is kind of low, especially since that will be the upper end of what the potentiometer will allow. But it could also be an amperage issue.

How many mA does can your adapter output? And you you have the voltage and amperage specs, and/or the make & model of the particular fan you're using?

Click to expand...

My adapter output is 800mA, I do not have the fan specs handy at this time. But for now it seems ok I guess, starts normally now when I plug it in now, and pulls a decent vortex in my flask.

The next time I have the fan unmounted I will take a look at the specs.

Thanks for the information! I made my own today and all I needed to buy was the rheostat and the knob!

Today I made a stir plate! | Austin's Beer Blog

Working on mine now. Just ripped apart my old HD for the magnets and fan. Tomorrow I hope to procure my rheostat, switch, and cigar box as well as place an order for a 2L flask and stir bar. Can't wait to getting going

subscribed

First attempt: fail. Getting stronger magnets tomorrow.

Here are my stir plates. If you need one...I'm just saying.

coypoo said:

First attempt: fail. Getting stronger magnets tomorrow.

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I had the same problem with the hard drive magnets. They just don't have enough strength.

I purchased the neo disc magnets recommended about 5 pages ago and they work perfectly.

TrainSafe said:

I had the same problem with the hard drive magnets. They just don't have enough strength.

I purchased the neo disc magnets recommended about 5 pages ago and they work perfectly.

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Good to hear. I'll look for those when I get out today or tomorrow

Double time to sit around twiddling my thumbs at work -

I got some good magnets but my fan spins too fast, so I need to get a resistor (I don't have any power cords that are less than 9V). Do I put it before or after the rheostat?

You can go small in series or as a voltage divider so long as it's large enough to cover the power needs.

Accidic said:

You can go small in series or as a voltage divider so long as it's large enough to cover the power needs.

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Would a 1/2 watt 100 ohm be good? I'm terrible with electricity stuff, so im just guessing at all of the different watt/ohm combination resistors

I wish I had a 6V power cord.....

coypoo said:

Would a 1/2 watt 100 ohm be good? I'm terrible with electricity stuff, so im just guessing at all of the different watt/ohm combination resistors

I wish I had a 6V power cord.....

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WTH is a 6V power cord? I assume you mean a wall wart/AC adapter?

Yes.

I would see this atm when i'm 3 sheets to the wind. Just keep in mine I'm about a liter of vodka and a little over a bottle of champagne in so gauge accordingly.


Now for attempt number two at typing this.... That resistor should be safe up to 7v depending on how you wire it. As with anything, check it for heat before leaving it unattended after some test time and you should be fine. I presume your comfortable with a little testing as you can buy a complete unit for $40 or less with a warranty. also, be careful if you go the VD route as I just either fried a fan from that or (more likely) lack of magnet balance.

Wow, Great Thread. I swear I have read this somewhere in the 90 Pages but I can't find it.
I had the fan spinning last night & I was experimenting with different Power Supplies. Today I can't get the Fan to spin at all.
I have the PS wires twisted to the Fan Black & Red wires. The fan "Twitches" but won't spin. WTF?? It worked well enough to fling 1 magnet into my Parts Bin never to be seen again... Fan only ran with 1 combo of polarity. No response the "Wrong" way.
I'm playing with 6V 800MA, 9V 900MA & 12V 1000MA Power Supplies. All 3 Power Supplies give the same result. Fan moves back & forth but won't spin. When Power is off, the Fan will spin effortlessly.
BTW, I have a 1/2" thick Plywood Spacer between the Fan & a Fender Washer, no Magnets.
Any insights would be appreciated.

Try removing the magnets, you've likely de-polarized the fan motors magnets

56Firedome said:

Wow, Great Thread. I swear I have read this somewhere in the 90 Pages but I can't find it.
I had the fan spinning last night & I was experimenting with different Power Supplies. Today I can't get the Fan to spin at all.
I have the PS wires twisted to the Fan Black & Red wires. The fan "Twitches" but won't spin. WTF?? It worked well enough to fling 1 magnet into my Parts Bin never to be seen again... Fan only ran with 1 combo of polarity. No response the "Wrong" way.
I'm playing with 6V 800MA, 9V 900MA & 12V 1000MA Power Supplies. All 3 Power Supplies give the same result. Fan moves back & forth but won't spin. When Power is off, the Fan will spin effortlessly.
BTW, I have a 1/2" thick Plywood Spacer between the Fan & a Fender Washer, no Magnets.
Any insights would be appreciated.

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djii said:

Try removing the magnets, you've likely de-polarized the fan motors magnets

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That's what I thought, but he specifically said "no magnets".

no idea what you mean. if you think the fan has no no magnet, I assure you are not correct, you must have one for it to work. may not be perm, but it's a magnet.

djii said:

no idea what you mean. if you think the fan has no no magnet, I assure you are not correct, you must have one for it to work. may not be perm, but it's a magnet.

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No magnets mounted to the fan...

oic, my bad

I got mine working, after some serious digging I found a 5V wall wart and it spins well enough. I have to turn the rheostat to give me the the rpm possible, but I'll take it

I would try another fan if you have one just to try and isolate the problem

coypoo, I have tried a full range of Wall Warts from 3 VDC, 4.5 VDC, & 7.5 VDC as well as the 6, 9 & 12 VDC I mentioned before. All give the same result. Looks like the problem is the Fan. It's a brand new RS 4" per OP Bill of Materials.
I would return it to RS but I've removed some of the Casting which was in the way of the mounting Nuts/Washers & drilled the Holes out to allow 10-24 Bolts.
I have a 3" Fan in a Computer Case to use as a test mule. I just have to unbury it. No small Task.
Just noticed you are local. LHBS Brew Hut?

djii, I played with the Magnets but only after I had glued the 1/2" Spacer & Washer to the Fan. I had the same thought about de-polarizing the Motors' Magnets. The fan, on 12V, spun too fast & actually slung one of the Magnets into the Void, never to be seen again.
I got these Magnets at Hobby Lobby. $4.99 for 4. Rated 9 of 10 on the Package. But not Rare Earth Magnets.
I was trying out the different Voltage Wall Warts & 9 V seemed the best. I had them stacked 2 on a side. It's hard to tell which side is "+" & which is "-". I used the Stirbar to detiremine polarity & to place them on the Washer.
I never placed the Magnets directly on the Fan. The problem happened before I glued the Magnets to the Washer.

Well, What A Pi$$er!!
THe Mule works on all the Wall Warts. It's the Fan. I wouldn't be so steamed if I hadn't laid out $20 for the RS Fan. Don't see how I could take it back as I've hacked the Fan Shroud for clearance. The Mule came from my Desktop & now I have to put it back together again. Arrrgh!
It appears those Hobby Lobby Magnets are REALLY strong as they de-polarized the Motor's Magnets through the 1/2" Spacer. When I locate a replacement Fan I'll only use 1 on each side.
I'm really pissed as I got the Spacer/Washer PERFECTLY centered with no wobble. Now I have to do it all over again.
Warning to all who follow:
Really Strong Magnets can cause more trouble than they would seem to be worth. Hard to believe but appearantly true.

56Firedome said:

coypoo,
Just noticed you are local. LHBS Brew Hut?

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Yep, I live off of chambers and am pretty close to BrewHut. Love that place.

56Firedome said:

Warning to all who follow:
Really Strong Magnets can cause more trouble than they would seem to be worth. Hard to believe but appearantly true.

Click to expand...

This is good advice, though I would say that appropriate voltage is also really important. I recently made this and I discovered there is a pretty intricate interaction here between the electromagnets internal to the DC motor, the magnetic strength of mounted magnet , the stir bar magnetic strength, the size of both the stir bar and the mounted fan magnet, the voltage across the fan, the distance from the stir bar to the mounted magnet, and how well everything is centered.

Achieving the optimal balance is really quite difficult and can only be realized through some trial and error.

For instance, I have a 9V, 1A wall transformer powering a 3.5" computer case fan that is spinning two "fat" hard drive magnets (there are typically two sizes of hard drive magnets, fat and thin) stuck together.

It should be noted that the mounted magnet will slow down the fan considerably as its magnetic field interferes with the DC motor electromagnet. Too strong a magnet and you could prevent the fan from moving entirely. This can be absolved by adding a thicker spacer between the fan and the magnet, but I found that it was unnecessary in this case.

Mounting the fan too close to the stir bar creates too great a strain on the motor and it cannot move the stir bar fast enough to pull the vortex all the way down. Mounting the fan too far from the stir bar creates too weak an attraction between the magnets and the stir bar gets kicked off center.

It's tedious trying to find the perfect balance. I'm still working that out. I can easily get a full vortex on 1000 mL of water in a 2000 mL flask, but it splashes a lot and would end up coating the sides with a lot of sticky wort after 24 hours. I can't quite pull the vortex all the way to the bottom of a 1000 mL flask with 1000 mL of water with my current setup. I'm thinking probably voltage will do the trick as the magnets have proven themselves strong enough to hold the spin bar in place.

another piece of advice is a vortex down to the bottom is not needed for a stir plate. You really only need an inch or so. It has more to do with keeping the yeast in suspension and the surface tension disrupted to off gas

ekjohns said:

another piece of advice is a vortex down to the bottom is not needed for a stir plate. You really only need an inch or so. It has more to do with keeping the yeast in suspension and the surface tension disrupted to off gas

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This is truth. A vortex extending all the way to the bottom, while a great goal for "maximization," in reality increases gas exchange (the whole reason we want a stir plate in the first place) at an insignificant rate over a small dimple.

As long as you don't put an airlock on your starter (something I have seen pictures of in this thread) you're getting the job done if the starter is moving with a small dimple. Putting an airlock on your starter that is sitting on a stir plate is like clogging your toilet on purpose and then flushing. Doesn't make much sense.

So, Here's the question of the day:
How do I detiremine if the Fan Side Magnets are too strong?
I'd just as soon not repeat this little exercise as the Centering of the Magnet Spacer/Washer was fairly tediuos. I never got to assemble the wiring to the Off/On Switch, the Potentiometer & the Fan much less to detiremine which Voltage Wall Wart is best for my set up. I have a full array of WW's from 3 to 12 VDC with MAs from 600 to 1000.
And so it goes. Thanks for any input but I'm off to Microcenter to buy a CHEAPER replacement Fan.
Later.

One more thing before I buzz off to MicroCenter.
I just spoke to a buddy who just finished his Stir Plate. His 1st Starter is in the Fridge & he's very pleased with the Project.
He bought the identical Bill of Materials from RS & placed the Magnets on a Washer which was Epoxyed directly to the Fan with no Spacer. He placed the Magnets (from K & J) in pairs, Side by Side, not stacked. This allows him to use 1" as well as 2" Stir Bars without requiring repositioning the Magnets when he wants to try out different lengths.
His worked without a hitch. I suspect the K & J Magnets are at least a strong as the ones I used but since they were SxS, not stacked, the Motor Magnets were not de-polarized & all is well. A case of More is not Always Better.

56Firedome said:

So, Here's the question of the day:
How do I detiremine if the Fan Side Magnets are too strong?
I'd just as soon not repeat this little exercise as the Centering of the Magnet Spacer/Washer was fairly tediuos. I never got to assemble the wiring to the Off/On Switch, the Potentiometer & the Fan much less to detiremine which Voltage Wall Wart is best for my set up. I have a full array of WW's from 3 to 12 VDC with MAs from 600 to 1000.
And so it goes. Thanks for any input but I'm off to Microcenter to buy a CHEAPER replacement Fan.
Later.

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your fan side magnets are too strong if, when the magnets are mounted to the fan, the fan cannot turn fast enough to stir your starter at any distance from the stir bar.

A good way to test this would be to mount your steel washer to the fan blades (using some kind of epoxy) and then stick the magnet to the washer (DO NOT GLUE IT TO THE WASHER). Then attach your power supply directly to the fan and plug it in. If it spins without difficulty, you're probably on the right track.

The steel washer is really easy to mount in the center. The hole for the washer is very small and all you have to do is line it up with the center of the fan. Eyeball it and measure if you need.

Rare earth magnets may be too strong for this small DC motor. I don't know. Hard drive magnets are really quite ideal (except for their shape which will cause the stir bar to wobble no matter how centered it gets). With two "fat" hard drive magnets stuck together, I did not need any spacers at all beyond the 2" steel washer.

I'm using two fat hard drive magnets with a 3" computer case fan from radioshack:

12VDC Brushless Fan : Computer Fans | RadioShack.com

Of course I got the fan for free by harvesting it from the pit of old computer parts at work.

56Firedome said:

One more thing before I buzz off to MicroCenter.
I just spoke to a buddy who just finished his Stir Plate. His 1st Starter is in the Fridge & he's very pleased with the Project.
He bought the identical Bill of Materials from RS & placed the Magnets on a Washer which was Epoxyed directly to the Fan with no Spacer. He placed the Magnets (from K & J) in pairs, Side by Side, not stacked. This allows him to use 1" as well as 2" Stir Bars without requiring repositioning the Magnets when he wants to try out different lengths.
His worked without a hitch. I suspect the K & J Magnets are at least a strong as the ones I used but since they were SxS, not stacked, the Motor Magnets were not de-polarized & all is well. A case of More is not Always Better.

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I'm not really sure how it is possible to de-polarize a brushless dc motor with a small rare earth magnet...

mightynintendo said:

I'm not really sure how it is possible to de-polarize a brushless dc motor with a small rare earth magnet...

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I think de-polarize is a bad term. The magnets strong field can possibly interfere with the operation of the motor.
Something I have noticed with PC fans. If the fan blades get pulled up, away from the motor, they start to run rough, or bind. The magnets could be pulling up on the fan rotor, screwing with the shaft/bushing operation. I had a PC fan (on a PC, not a stir plate) that this was a problem with. popping the fan back down in place cured the issue.