Hi
I was always taught that when winding a second layer onto the coil that you bring the wire back to that start and then wind the second layer otherwise the magnetic field would be cancelled. I can't see that it would cancel the magnetic field because the magnetic field lines of the second coiled layer would still be pointing in the same direction as the first coiled layer.
Thanks
Adam Hamilton
As long as your turns are all in the same direction, they ALL count.
Correct. The only benefit I see from doing it as Adam was taught would be that the maximum voltage difference between the winding layers would be the voltage developed on a single layer, rather than twice that, like the conventional winding scheme. This may be an issue for high- voltage coils - I've made coils for up to 25kV, but have found it more practical to add a layer of Kapton tape, rather than suffer the lump in the winding for the return wire. Also, a simple halving of the maximum layer-layer voltage is often insufficient, and tape is preferred. In fact, sometimes even tape can't easily handle the voltages encountered, and I've found a banked winding approach to be effective. I see from Terman's 1943 Radio Engineer's Handbook that this method was known from way back when. A friend makes coils to 50kV and he uses a type of banked winding approach, with each coil portion wound in its own section of a custom-machined bobbin.
Out of curiosity who teaches that?
You keep the turns going in the same direction and the current flow and it doesn't matter where you start or finish.
Two layers can be wound with starts on one side of the form and finishes on the other - both wound in the same direction and the two starts and two finishes connected together for more current handling . . . maybe that was the idea they were getting across?
"JackShephard" wrote in message news: snipped-for-privacy@4ax.com...
Thankyou Jack.
Looking at my original post, I kinda left out the actual question which was can I wind the first layer and then wind the second layer starting from the end of the first. Your answer did in fact answer my question.
Adam Hamilton
Divide breakdown voltage of the mag wire by your volts per turn, and come up with a maximum turns per layer number. I would actually cut that number back by at least 15%.
We used to wind 800 turn secondaries, and the max turns per layer we would use was around 60.
Another important thing in multi-layer secondary winding is to refrain from "scatter winding", which means do not wind a layer chaotically. One should wind evenly across the face of the bobbin (for more than a few reasons), or previous layer, then place the transformer tape over that layer. It should appear flat. Do NOT stretch the tape. Also, keep the start of the layer turns and the finish INBOARD on the winding face at least half a mm. This keeps the start or finish turn of one layer becoming proximal to an underlying layer or one above it.
Yes. There is no reason to reverse turns direction on any winding, unless you want to degrade performance, and that should never be a goal.
On a scatter wind where all turns are on the same layer, the final turn is many volts away from the first, so a breach can occur between them. This is the whole reason a good xfmr shop winds high turns count secondaries (or primaries) on multiple layers, each of which are segregated by insulator media.
There is no lump if the method used is right. The tape is needed to keep turns away from each other. One winds across and back until the max turns per layer of the designer are met, and then a turn of tape is added AS the wire continues turning about the bobbin. Then the next layer's turns get stacked right on the underlying layer, and there was no cross-over or bump of any kind. Turns can start at the "bottom" or "top" of a bobbin segment. It doesn't matter. The only thing that does is the direction of the turns.
Tape doesn't seal off layer edges and should not be relied upon to do so. It only separates layer faces. Keep turns inboard a bit to increase creepage distances, and always vacuum impregnate an HV design in varnish or at the very least, potting compound. That is, of course, unless it is an oil bath design.
If it is too high, a segmented bobbin is required. I posted a picture in a.b.s.e a couple weeks back that one troll jumped all over, but it does perfectly show a proper EHV xfmr (miniature low power) that has about 5 bobbin segments, each with nearly 300 turns, which is pushing the limits of the mag wire. I'll post it again.
Yes. We had many customs made, and another easy way to do it is to have G10 or FR4 bobbin parts made and epoxy them up yourself.
Start with off the shelf G10/FR4 tube, and get discs made for the bobbin segment separators out of non-clad flat sheet stock It can be milled just like a PCB design, and popped out from little perfs.
We even took an off the shelf bobbin, cut off one face (end), and added discs to it, and then replaced the end we cut off. It really does work well. I actually have some pics on one of these old hard drives here somewhere.
That sounds like a pi-wound coil for a radio, except there the goal is to reduce capacitance rather than prevent spark over. Reducing the voltage from one wire to the next should reduce both capacitance and spark over, however.
With *toroid* inductors, if you wind a single layer, you've accidentally created a 1-turn loop going around the donut. If you instead keep going and wind a second layer back along the first, this
1-turn loop is cancelled out. When winding toroids, it's a good idea to use an even number of layers, and go back and forth. For high power high frequency toroid transformers, you DON'T want a 1-turn loop which spews b-field out into the world. For small toroid inductors, you don't want a 1-turn loop that couples signals from outside.(((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty
My electronics teacher at college said this and searching the internet also showed the wire being brougt back to the beginning before winding the next layer. I asked this question because when I followed the magnetic field lines by winding the second layer from the end, they still pointed in the same direction. I thought that there maybe some advantage to bringing back the wire to the start.
Thanks for all your help everyone.
Adam Hamilton
...
Whoever told you this is an idiot.
Cheers! Rich
The advantage is to the professor, who has tenure, and teaches idiotic crap to the students so that they won't threaten his position when they grow up.
Cheers! Rich
Late at night, by candle light, "Adam Hamilton" penned this immortal opus:
Just take apart any old relay coil or something like it and see for yourself. You do have it right, it's the direction of the current in all the layers that set up the field, not the starting point in each of them.
- YD.
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