Any gripes with fan based stir plates?

[Catt22]

So you would use twice as many magnets and only use the + magnets when one half of the stir bar goes by and then use the - magnets when the stir bar has rotated 180 degrees and the other end is in that area? Seems that making the magnets reversible would be easier than doubling them.

Actually, I think you are right. I forgot that the stir bar has two poles, so it seems it would be necessary to reverse the magnet's polarity to make it work. My reason for suggesting eight magnets was to make it operate more smoothly and more powerfully. Six or four might work just as well, but I don't think only two would do it. This is all just speculation on my part. Just thinking out loud.
It sure was a cool idea, but looks like it might not be possible to build one easily and economically. Suitable magnets would be the key I thiink.

 

[wihophead]

The irony of it all is that you are trying to do exactly what the fan (BLDC motor) is already doing.....

 

[The Pol]

If you can make one these work on a 5 or 6.5 gallon carboy I would love one

Tough to get a single stirrer to work with the void on the bottom created by the curvature of the glass.

You make 5-6 gallon starters? WTF you brewin?

 

[Sawdustguy]

I am starting to think that with the amount of magnets needed, the current needed to drive them, the component count growing higher, this project is not practical at the DIY level.

 

[The Pol]

I have a fan based stir plate. It looks neat, clean, it is absolutely silent (cant tell it is running unless the stir bar is on it) and it doesnt throw the bar.

To answer the OP

 

[Sawdustguy]

I have a fan based stir plate. It looks neat, clean, it is absolutely silent (cant tell it is running unless the stir bar is on it) and it doesnt throw the bar.

To answer the OP

Pol, you should know by now that us engineer types just can't leave chit alone. I am afraid after looking at it, that trying to DIY a Magnetic Stirrer without the use of a motor is expensive and not cost practical.

 

[CodeRage]

I have a fan based stir plate. It looks neat, clean, it is absolutely silent (cant tell it is running unless the stir bar is on it) and it doesnt throw the bar.

To answer the OP

Cool, thanks. I've come to the conclusion that this is a bit excessive.

Wihophead: where do you think I got the idea First thing I tried was to rip the fan off and give it a whirl .

At this point it has become mental masturbation.

For example, I have come up with the following to determine the resistance in a length of wire over a given cores Diameter, L inches wide, with x many layers using 30 gauge wire.

total resistance = Sigma 0 to x ((n*0.02)+D)*pi(L)1026.71

Ill probably build a fan based one and toy with this idea.

 

[CodeRage]

Pol, you should know by now that us engineer types just can't leave chit alone. I am afraid after looking at it, that trying to DIY a Magnetic Stirrer without the use of a motor is expensive and not cost practical.

Exactly! It's not a matter of a did it cheaper or better but, Different! better and or cheaper is always a plus though

 

[Plan9]

Something I thought of last night...

Electromagnets create heat. A pretty good amount of heat.
You put 8 together cycling on and off, and changing polarity constantly, you will probably create way more heat than your yeast starter should be exposed to.
This may actually be counterproductive.

 

[StirStarters]

That's a fascinating idea, turning the stir bar into the rotor! Polyphase motors with multiple poles in a size that would fit into a small box may be hard to find, though. Aren't most polyphase motors made for big pieces of rotating machinery to keep the torque constant? But it's an idea that would be cool to work with, if you have one less moving part that's an advantage.

For the DIYer, you can't beat the cheap, tough little muffin fan. I have done a locked rotor test on the fans I use for my stir plates and I can't get the things to fail. I simply stick a pencil in between the fan blades and the housing to keep the fan from spinning and wait to see how long it takes to fail. I have gone days with the rotor locked and when the pencil is removed, the fan just continues spinning. Short of running over them with a truck tire, they are pretty much indestructible.

Noise is not a factor. When they are enclosed in a box you can't tell when it's on or off. Vibration can be an issue if the drive magnets are not centered and spinning properly. And the heat generated by the electronics is minimal. With a fan running at 12 VDC and 100mA you might throw off 1 watt of heat, but with the fan turning that heat is dissipated quickly.

 

[CodeRage]

That's a fascinating idea, turning the stir bar into the rotor! Polyphase motors with multiple poles in a size that would fit into a small box may be hard to find, though. Aren't most polyphase motors made for big pieces of rotating machinery to keep the torque constant? But it's an idea that would be cool to work with, if you have one less moving part that's an advantage.

Yeah, they usually are and they are what I am most familiar with. Probably why I used the term. Three phase is more efficient for several reasons, one is there is less slip between changes of phase. plus 480V service is going to be hard to get for residential, not to mention extremely, stupefyingly, out of your gaht damned mind expensive.

Now that I think about it, a bipolar stepper motor better describes it. A la the H bridge used for controls mentioned earlier.

I did manage to make an electromagnet today that was relatively small, strong and, used a modest amount of current. There may be hope.

I may make another later today, got some kind of flu crud so my motivation is some what lacking..

Like I said earlier, I don't expect this to be a better stir plate, or practical for that matter. Just something different and a little interesting.

 

[CodeRage]

Well, I guess there is going to be a build thread...
[youtube]5-mCHPUu9ms[/youtube]

This is only using 2 of 4 magnets. Didn't have enough 26 gauge wire to do more. than 2.
I was manually flip flopping the poles. First with 6V and then with 12V pulling 2 and 4 amps respectively. The nice thing is the coils didn't get that hot at all.