Preferred wire placement in coils

[Casey]

Hi guys,

A colleague and I have been having a discussion over the best placement for wire when winding a coil. We are winding two 13gauge wires 44 turns to make our coils and are having trouble deciding what placement would be best. I would love to hear some of your thoughts on the subject. Below is a cross-section diagram of the three ways we were discussing...imagine the coil on the winding machine cut in half (and not to scale!), with the orange dots the wires stacked inside the walls of the winding machine.

Thanks for your feedback!
Casey




A link in case the image above doesn't show up: https://picasaweb.google.com/lh/photo/jqnGVGUVECONNoHR0dXPDw?feat=directlink

[Flux]

This is a nice theoretical discussion but life is normally not that simple.

The first method stacking wires on top of each other is not using the space to best advantage and in real life you will have real trouble doing it. The other two methods are more practical but even then you will have a lot of trouble doing it to the level of perfection that you show. You are not dealing with concentric loops in a real winding but helices. With a lot of care you may be able to manage the first few layers to the ideal plan, but the shifting end of the helix means that at one point a wire will not sit in the groove as in the sketch and this constant error at the cross over point makes a cumulative mess of the winding.

It pays to be reasonably careful with the winding, you don't want turns crossing everywhere, but it becomes very tedious to achieve anything approaching perfection over a significant number of layers. If you take an hour to wind a coil it will probably be sightly better than one you can wind in 30 seconds but I really doubt that you will see any reward for the infinite labour.

With large section copper in transformers it is worth trying for ideal layer winding, particularly with square or rectangular wire and it is common practice on very large coils to put a transposition in each turn so that you get the ideal concentric turn coils. You can't use such large section in an air gap alternator because of eddy loss. if you have to resort to many in hand small wires in parallel to avoid eddies then you will have to be very careful with the winding but for normal coils anything better than just being neat and careful is just a labour of love that will drive you to distraction with no real benefit.

The more copper you can get in a given space the better, but for all that you actually need resistance somewhere in the system for direct connected battery charging. I think you will find thatthe difference you can make between a perfect winding and a tidy one will come within the general tolerances of construction. A really scruffy winding will certainly cause you trouble with wasted space but absolute perfection is best left to the perfectionists not those who want to build a good working alternator.

Flux

[kevbo]

None of the stacking in grooves pictures work unless you have enough wires in hand to wind one turn per layer, and then only for two layers. The helix of each layer alternates right-hand, * left-hand, right-hand, etc.  

If you have ever seen doubled springs on engine valves or guns, you know that they wind one right-hand and the other left-hand so that they won't nest and get tangled up.  Cable wound on drums sometimes gets fouled, but it would ALWAYS get fouled if all the layers had the same handedness.

If you have enough wires in hand to fill a layer with one turn, then the second layer can nest in the grooves offset, say, to the right. But you now have a helix, and to put the third turn (offset to the left) you would have to reverse the handedness of the next helix, which screws the nesting up.

To make the stacking in grooves work, you have to have all the helices with the same handedness, and that means you have to have a wire running back to the start side, which screws up the stacking.

In some cases, you can make all your crossovers in a part of the winding where it doesn't matter, and have all the wires nicely nested in the tight spaces.  Take apart a conventional motor or the stator windings on car alternators for examples...Wire is layered neatly in the stator slots, but the loops on the ends are anything but neat.

This is the reason for square cross section wire.  You can "stack on top" and still fill more volume with copper than trying to stack round wire in the grooves of the layer underneath. (which for the reasons discribed above doesn't work anyway.)


*Normal screws are right-hand threaded.  Reverse pitched, left-handed, threads can be found on POL propane connectors (not the new acme) and the left pedal of bicycles among other places.