I've constructed a rotating valve. It contains a magnet.
I can rotate the magnet from outside the pipe where the valve
may be immersed in a corrosive liquid.
It is a kind of an unipolar motor.

Obviously I want to spent the least amount of copper in the coil
to exercise a moment onto the magnet.
What is more favourable:
N windings on one side
N/2 windings on either side.

Or doesn't it make a difference, to a first approximation?

Groetjes Albert
--
"in our communism country Viet Nam, people are forced to be
alive and in the western country like US, people are free to
die from Covid 19 lol" duc ha
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

On Friday, May 28, 2021 at 8:31:34 PM UTC+10, none albert wrote:
> I've constructed a rotating valve. It contains a magnet.
> I can rotate the magnet from outside the pipe where the valve
> may be immersed in a corrosive liquid.
> It is a kind of an unipolar motor.
>
> Obviously I want to spent the least amount of copper in the coil
> to exercise a moment onto the magnet.
> What is more favourable:
> N windings on one side
> N/2 windings on either side.
>
> Or doesn't it make a difference, to a first approximation?

The magnet has length. I'd put my money on two saddle coils, one on either side of the pipe. What you win on the pole closest to the nearer coil is probably worth having.

--
Bill Sloman, Sydney

On 2021-05-28, albert@cherry.(none) (albert) <albert@cherry> wrote:
> I've constructed a rotating valve. It contains a magnet.
> I can rotate the magnet from outside the pipe where the valve
> may be immersed in a corrosive liquid.
> It is a kind of an unipolar motor.
>
> Obviously I want to spent the least amount of copper in the coil
> to exercise a moment onto the magnet.
> What is more favourable:
> N windings on one side
> N/2 windings on either side.
>
> Or doesn't it make a difference, to a first approximation?

windings on either side gets you something like a Helmholtz coil
which means a more uniform magnetic field, but if your field is not
saturating the magnet I don't think it makes a difference.

--
Jasen.

In article <216d72b0-d41c-448f-af13-e66eb0ed1038n@googlegroups.com>,
Bill Sloman <bill.sloman@ieee.org> wrote:
>On Friday, May 28, 2021 at 8:31:34 PM UTC+10, none albert wrote:
>> I've constructed a rotating valve. It contains a magnet.
>> I can rotate the magnet from outside the pipe where the valve
>> may be immersed in a corrosive liquid.
>> It is a kind of an unipolar motor.
>>
>> Obviously I want to spent the least amount of copper in the coil
>> to exercise a moment onto the magnet.
>> What is more favourable:
>> N windings on one side
>> N/2 windings on either side.
>>
>> Or doesn't it make a difference, to a first approximation?
>
>The magnet has length. I'd put my money on two saddle coils, one on
>either side of the pipe. What you win on the pole closest to the nearer
>coil is probably worth having.

Thanks.
Actually the magnet I use is a 10 mm disk with a thickness of .75 mm.
My coil is at least 10 mm removed from the near side of the disk.
In that case your answer implies that not much improvement is to be
expected, if any. Correct?

I started from the model of a minute magnetic dipole in a homogenous
magnet field. You draw attention to the fact that with one coil
and a finite magnet the force on the two sides is not symmetric.
With two coils the field may not be homogeneous, but -- being
symmetric -- at least it will result in a pure torque, with no net
force to be compensated by the valve seat.
That means less friction, which could result in saving copper, and
probably better reliability as well.

>--
>Bill Sloman, Sydney

Groetjes Albert
--
"in our communism country Viet Nam, people are forced to be
alive and in the western country like US, people are free to
die from Covid 19 lol" duc ha
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

On Friday, May 28, 2021 at 11:05:06 PM UTC+10, none albert wrote:
> In article <216d72b0-d41c-448f...@googlegroups.com>,
> Bill Sloman <bill....@ieee.org> wrote:
> >On Friday, May 28, 2021 at 8:31:34 PM UTC+10, none albert wrote:
> >> I've constructed a rotating valve. It contains a magnet.
> >> I can rotate the magnet from outside the pipe where the valve
> >> may be immersed in a corrosive liquid.
> >> It is a kind of an unipolar motor.
> >>
> >> Obviously I want to spent the least amount of copper in the coil
> >> to exercise a moment onto the magnet.
> >> What is more favourable:
> >> N windings on one side
> >> N/2 windings on either side.
> >>
> >> Or doesn't it make a difference, to a first approximation?
> >
> >The magnet has length. I'd put my money on two saddle coils, one on
> >either side of the pipe. What you win on the pole closest to the nearer
> >coil is probably worth having.
> Thanks.
> Actually the magnet I use is a 10 mm disk with a thickness of .75 mm.
> My coil is at least 10 mm removed from the near side of the disk.
> In that case your answer implies that not much improvement is to be
> expected, if any. Correct?

Beats me. Field-plotting software would tell you, but that costs money.

The force probably decreases as the square of the distance. If the magnet is flat disk, with the magnetic field through the disk, rather than across the disk, when it is across the pipe the bit farthest away from a single sided coil is 20mm away from the coil so then would gets a quarter of the force acting on the nearest bit.

Putting coils on either side of the pipe would even that out.

> I started from the model of a minute magnetic dipole in a homogenous
> magnet field. You draw attention to the fact that with one coil
> and a finite magnet the force on the two sides is not symmetric.
> With two coils the field may not be homogeneous, but -- being
> symmetric -- at least it will result in a pure torque, with no net
> force to be compensated by the valve seat.

We can hope.

> That means less friction, which could result in saving copper, and probably better reliability as well.

It might. An ounce of experiment beats a ton of speculation.

--
Bill Sloman, Sydney

On 28 May 2021 10:31:17 GMT, albert@cherry.(none) (albert) wrote:

>I've constructed a rotating valve. It contains a magnet.
>I can rotate the magnet from outside the pipe where the valve
>may be immersed in a corrosive liquid.
>It is a kind of an unipolar motor.
>
>Obviously I want to spent the least amount of copper in the coil
>to exercise a moment onto the magnet.
>What is more favourable:
> N windings on one side
> N/2 windings on either side.
>
>Or doesn't it make a difference, to a first approximation?
>
>Groetjes Albert

Can you post a sketch of the geometry?

If the guts are symmetric, I'd vote for two coils and an outer ferrous
path to reduce air gap, like an overall section of iron pipe.

--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

On Friday, May 28, 2021 at 3:31:34 AM UTC-7, none albert wrote:
> I've constructed a rotating valve. It contains a magnet.
> I can rotate the magnet from outside the pipe where the valve
> may be immersed in a corrosive liquid.

> Obviously I want to spent the least amount of copper in the coil
> to exercise a moment onto the magnet.

If you want the 'valve' to rotate only on command, consider using an external
motor to rotate a permanent magnet; that will allow a bit of friction
to hold the position with no power applied.

> What is more favourable:
> N windings on one side
> N/2 windings on either side.
>
> Or doesn't it make a difference, to a first approximation?

As long as you don't saturate the core parts (which direct and
contain the field), it's only different in effective use of available winding
space; N/2 on either side means lessened winding diameter, which is
usually more efficient.

A field strength improvement will result from adding a core to the windings;
otherwise the magnetic field will stray far from the space it is intended to affect.