@kiweered What about the other DEY design that comes up with the video?

They use a DC motor to spin a magnet, I would like to do it without motor to remove moving parts from the system.

The force decreases as the square of the distance, so you want the distance to be very small

The system is relatively small and the magnet also, I don't need a lot of force but thanks, I will wotk on that.

A good shape for that would probably be like a plus sign "+" so you have four faces.

Yes I also think that's a good improvement and you can find such stirring magnets in the market.
Thanks for your big answer, it brings a lot of precision to the project I need to think about.

It suddenly hit me that the TS had not mentioned Glass container, only a sealed container. If it is a conductive material all bets are off.

I don't know yet what would be the material, probably between glass or stainless steel (bad conductor).

They are selling stirrer coil kit:
View attachment 287531

Nice, that's what I try to build but it's way too expensive. But good idea to add metal parts to bring magnetic flux in the middle of the container.

Thanks you all for your answers. I found some videos of working stirrer with 4 electro-magnets/coils under the glass container, so I think I'll do the 1st prototype with such configuration. But I also think you can have good results with the propper motor stator. However they are a bit more exprensive (especialy the brushless one...) so I will think about them for a 2nd prototype.

 

Locating and obtaining the external rotor 4 pole motor of the correct physical size and suitable coil specifications will be the hard part, It may happen that you need to make the coils, which is not that difficult. It might even be that a thick steel washer as the base and four steel bolts as the magnetic poles can work out very well, if the TS has any mechanical skills.

 

Yes I also think that's a good improvement and you can find such stirring magnets in the market.
Thanks for your big answer, it brings a lot of precision to the project I need to think about.

Hi,

You're welcome. I like to provide as much info as possible when it comes to magnetics and related because there is more to that then we usually encounter with just pure electrical stuff like current and voltage.

In fact, it has been said that magnetics, such as with an inductor, links our regular electronics with the entire universe and maybe beyond because in classical theory the magnetic field extends out to infinity, which means it, in theory, crosses the entire universe. In fact, in some inductance calculations you have to integrate from the surface of the wire to infinity which would cover the entire breath of the universe and then some.

Of course this is classical theory and even with that the field decreases quickly, but it's still interesting to think about. Could some alien civilization be intercepting your coil energizing and deenergizing?
"Oh geeze, there that guy on Earth goes again running that dang coil thing again and interfering with our TV reception again, dang!" ha ha.

 

Like I had mentioned earlier, extending the pole pieces up, towards the bottom of that sealed container will improve the efficiency. BUT if that container is electrically conductive, that will block much of the effect of the rotating magnetic field.
It suddenly hit me that the TS had not mentioned Glass container, only a sealed container. If it is a conductive material all bets are off.

Hi,

For light liquids i think i would have went with a vibration type mixer. Seems easier to build and simpler and container material type doesnt matter as much.
I originally assumed glass too

 

Hey, news from the project :
I was able to create a spinning magnetic field with 4 coils and a stepper motor driver (DRV8825). This field is strong enough to make a small magnet spin inside the container.

Here is the wiring diagram for the coils :

Each phase is made of 2 coils mounted is the oposite polarity to create 2 oposite magnetic poles when the current is going one way or another.

Here is the sequence of the 4 coils magnetic poles :
- If the stepper driver is set in Full wave mode
- If the steeper driver is set in Half wave mode


What I would like to try is to have only 1 phase working at the same time like in the picture under :
1) i_a >0, i_b =0
2) i_a = 0, i_b >0
3) i_a <0 0, i_b =0
3) i_a = 0 0, i_b < 0


So at the end I would have this following sequence :

Do you have any idea how I can acheive such a driving ? If it exists any IC driver that is made for this ?
I thought about 2 H-bridges but they are driving voltage and I think it's better to control the current flowing in the coils.

 

So at the end I would have this following sequence :

Do you have any idea how I can acheive such a driving ? If it exists any IC driver that is made for this ?

It is not good idea, because magnet will glue not only to reverse polarity poles,
but to neutral poles too.
Magnet, independ on its polarity will glue to neutral poles (glue to iron).

 

Hey, news from the project :
I was able to create a spinning magnetic field with 4 coils and a stepper motor driver (DRV8825). This field is strong enough to make a small magnet spin inside the container.

Here is the wiring diagram for the coils :
View attachment 287727
Each phase is made of 2 coils mounted is the oposite polarity to create 2 oposite magnetic poles when the current is going one way or another.

Here is the sequence of the 4 coils magnetic poles :
- If the stepper driver is set in Full wave mode
- If the steeper driver is set in Half wave mode
View attachment 287726

What I would like to try is to have only 1 phase working at the same time like in the picture under :
1) i_a >0, i_b =0
2) i_a = 0, i_b >0
3) i_a <0 0, i_b =0
3) i_a = 0 0, i_b < 0

View attachment 287728
So at the end I would have this following sequence :
View attachment 287725
Do you have any idea how I can acheive such a driving ? If it exists any IC driver that is made for this ?
I thought about 2 H-bridges but they are driving voltage and I think it's better to control the current flowing in the coils.

A stepper motor driver will have a current mode control you can use to force current through the windings.

 

Hey, news from the project :
I was able to create a spinning magnetic field with 4 coils and a stepper motor driver (DRV8825). This field is strong enough to make a small magnet spin inside the container.

Here is the wiring diagram for the coils :
View attachment 287727
Each phase is made of 2 coils mounted is the oposite polarity to create 2 oposite magnetic poles when the current is going one way or another.

Here is the sequence of the 4 coils magnetic poles :
- If the stepper driver is set in Full wave mode
- If the steeper driver is set in Half wave mode
View attachment 287726

What I would like to try is to have only 1 phase working at the same time like in the picture under :
1) i_a >0, i_b =0
2) i_a = 0, i_b >0
3) i_a <0 0, i_b =0
3) i_a = 0 0, i_b < 0

View attachment 287728
So at the end I would have this following sequence :
View attachment 287725
Do you have any idea how I can acheive such a driving ? If it exists any IC driver that is made for this ?
I thought about 2 H-bridges but they are driving voltage and I think it's better to control the current flowing in the coils.

Why do you want only one phase at a time? Half wave, or even some of the other microstepping modes that the DRV8825 controller can give you will produce a much smoother spinning field than Unipolar drive, which is what you're asking about. Unless you want a more "jerky" motion, of course. The DRV8825 already contains 2 H-Bridges anyway, and full current control!

 

The half-step mode shown is mostly used for improved resolution, because the torque changes as alternating single and dual coil sets are powered. But it does provide smoother operation at higher speeds, and if it works well enough at the design spacing, then you have the solution. And that circuit is about as simple as it can get.

 

OK I understand, I guess half-step mode is working great in my case.
Now if I would like to add 2 pairs of coils :
From this
*
to this

Do you have any idea how I can drive sequencialy the 4 pairs of coils ?

 

That is not a standard stepper configuration and that means no standard drive module available. AND THAT means a lot more effort for whatever gain it might provide..

 

First of all, to shift the well working magnetic spinner to badly working and heavyweight coil-based spinner is very bad idea. But, happily, there exist the three phase motors, where properly increasing the voltage, the rotating rotor may be safely extruded, and voila, You obtained the open spinner. Dont like it enough? Okay, then here are formula:
Turns*Amperes=B*(L(core)/mjurel/mjuzero+L(air)/mjuzero)). Here L(core) must be full magnetic path length along the core (meters) and mju rel for steel is 4400 or ferrites some two or more times less. Mju zero is 12.6E-7. L(air) is air gap length by most of magnetic lines are going through. B is Teslas, in case of steel about 0.8 or if transformer steel then 1.0-1.2, or if ferrite then 0.2-0.3. If the air gap is larger than millimeter, it become dominating in this equation.

 

If the arrangement presented in post #25 is performing adequately then why mess with it?? If a bit more power is needed then examine the abilities of the present scheme and see if there is capability of more power. And if the magnetic field coupling can be improved by adding to the pole pieces that is free improvement.