Mobius coil winding?

Design and use of Chokes for PS, anode and filament use.
Post Reply
PakProtector
Posts: 33
Joined: Wed May 04, 2005 2:36 am

Mobius coil winding?

Post by PakProtector »

Hey-Hey!!!,
I came upon a ref to winding methods to reduce winding capacitance. It was called 'Mobius', and looks like a reasonable means to achieving a 50% reduction, all else being equal.

Are you familiar with it Sir Slagle?
cheers,
Douglas
Question Authority, disobey it only after understanding it, and when absolutely required...
dave slagle
Posts: 2038
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

actually no.

i did some google work and came up with three decidedly different concepts.

-the mobius resistor where inductance cancels

-the mobius toroid on a quarrtz core ???

-the mobius loop antenna

of the three i suspect the loop antenna use is what you are referring to. It is an interesting concept and i'm trying to relate it to a multilayer coil but have not had any luck as of yet.

any good references on it?

dave
PakProtector
Posts: 33
Joined: Wed May 04, 2005 2:36 am

Post by PakProtector »

Hey-Hey!!!,
It would be the loop antenna ref. I took a look at an RF inductor I have and it is done in three sections( axially pie wound ), with each of the sections mobius wound. Looks sort of like a spool of string.

I would like to try this method crossed with layer winding. Since the layer finishes in the center, a final cross over half the turns would be required.

cheers,
Douglas
Question Authority, disobey it only after understanding it, and when absolutely required...
dave slagle
Posts: 2038
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

when it comes to the multiple layers the cross over points would get pretty big pretty quickly. Not that this is a huge issue since they could be placed on the top or the bottom of the coil former, but i just visualize it being difficult to keep neat. (Not that there is anything wrong with a messy coil.)

i do have to wonder if going to more vertical sections would get you there quicker? At some point, i have to become comfortable with my measurements for capacitance and try a few things.

dave
PakProtector
Posts: 33
Joined: Wed May 04, 2005 2:36 am

Post by PakProtector »

on measuring for capacitance, assuming we can stay out of the regions where core performance is changing the inductance, the capacitance is fairly easy. It needs two precision caps( Tek time base are nice in .01, .1 and 1 mike values ).

You make two resonance frequency measurements. C is the sum of coil winding and installed shunt capacitance. Depending on the coil, one might want to use .001 and .01 uF or some comboo of smaller caps. You know part of the capacitance, and L isn't changing so the good ole 2 eq'n/2 unknown method will spit out L and Cw...

Ever tried this one?

On the cross overs, you'll wind up with a neat chevron pattern, which can be put on the outboard side of the bobbin. It will be thicker, but that will also be manageable.
cheers,
Douglas
Question Authority, disobey it only after understanding it, and when absolutely required...
Dave Cigna
Posts: 96
Joined: Sun Jan 23, 2005 10:58 pm

Post by Dave Cigna »

It's an interesting idea, and I'm glad you brought it up; it's always good to get new perspectives. However, it seems to me that the basic technique can be reasonably applied only to large diameter single layer windings. The crossovers are an imperfection - a deviation from the ideal. With a small diameter multilayer coil (i.e. a bobbin wound inductor) you end up with as much crossover as not.

It also ends up being a very difficult thing to implement if there are a lot of turns. You'd have to run the winding machine VERY slowly. In practice I might end up leaving the motor switched off and turning the mandrel by hand. That's not something I'm interested in trying if there are many hundreds or thousands of turns as opposed to the dozen or so of a loop antenna.

In the end, any technique to lower winding capacitance is just an attempt to keep the windings separated. The mobius technique focuses on keeping consecutive turns separated. If you can give up bobbin space than simply winding with a very aggressive pitch (easy to implement on a hand winding machine) will keep all windings separated. Of course that means there's a lot of air in the coil where there might have been wire, so you can't fit as many turns into the same space. But, compared to mobius, the crossovers are distributed around the coil so you might end up fitting more turns.
PakProtector
Posts: 33
Joined: Wed May 04, 2005 2:36 am

Post by PakProtector »

Hey-Hey!!!,
I don't think that this sort of thing would be easy to wind. That was not the point though. Matter of fact, I can't think of very many ways to make the winding job any more difficult. The end of layer is also going to ind up in the very middle too.

I thought that the cross over would take up about 25% of the circumferential area. It would be twice the radial thickness, but with a close axial lay. So it would be between 20% and 30% less dense per layer. The only way I can think of doing this is by hand, slowly and for me, I don't think this the right place to start my winding career.
cheers,
Douglas
Question Authority, disobey it only after understanding it, and when absolutely required...
Post Reply