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Secondary Coil manufacturing flaw questions

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Sigurthr

Tue May 01 2012, 04:05AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Hey all!

So I'm slowly and carefully winding my new secondary coil (18" x 4.5" 30awg HPN magnet wire) by hand with no jig, just a support rod for the wire spool and a few questions came across my mind. Now, I've been very careful to not allow any gaps or points where the wire crosses over a previous turn or kinks or slippage... etc etc erc.

What actually happens to the magnetic field (and resulting electric field) a coil produces when:
1) there are gaps between the windings? I assume the inductance reduces as the flux density would be decreased.
2) a winding slips out of progressive order and goes over a previous turn?

And likewise it would be interesting to know;
What effect on the magnetic field/inductance does going back over an already wound section have when you add a second layer? I know this is not applicable to TC secondaries as the insulation on the thin wire can not handle the voltage differential between one layer and another. But in a lower voltage coil for example. I've made inductors/chokes and small transformers before but I've always used single layer coils. I'd look this up online but I don't know what to search for the answer.

Anyway I'm about 3.5 hours in to winding and half way done. 9.5 out of 18 inches completed. Every now and then my hand gets tired and the most recent turn slips over the previous one but I'm careful to correct it and take a break. No gaps issues so far other than the first few mm of winding at the base, but I figured that can always be unwound if I wind a few mm more at the top.

dude_500

Tue May 01 2012, 04:39PM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

Overlaps are a big problem because of dielectric strength and breakdown like you said. This is caused by the electric field being higher in magnitude between those overlapping windings than it would be of a perfect winding. Magnetically, there is very little consequence to a small overlap. In fact, in regard to an ideal transformer it doesn't matter how you wind it. It could be an overlapping mess or a nice single winding. Inductance will still scale with n^2. In reality, there are slight effects, and I don't remember which way overlapping layers causes the inductance to go. There are consequences other than the inductance though. One as you know is dielectric strength. Another is inter-winding capacitance which can play a huge role when designing power transformers designed to operate at a high frequency. Leakage inductance is also affected by the geometry of the windings.

Dr. Drone

Tue May 01 2012, 08:13PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Goodchild

Tue May 01 2012, 10:39PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I would say Dr Spark has the most immaculate, perfect secondaries that are possible without using nano-engineering. (idk maybe he dose use nano-engineering...) Not a molecule out of place!

I agree a winding jig is a must if you want error free secondaries. I usually use a gear head motor and some 2x4's. It dons't have to be fancy, just be sure to center up that axil for no wobble. This is important when you go to coat the thing in poly or epoxy for an even coat.

Sigurthr

Wed May 02 2012, 03:14AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Haha thanks for the replies!

Yes, my wife came in after about 4 hours of winding and said I was a madman. I think she's right. I wanted to build a simple jig out of 2x4s but the local hardware shop only sells 10ft lengths and doesn't have a saw to cut them down to size, and I can't fit them in my car for the 22mile ride back home. Also, I'm WAY over budget as it is. I'm about 150miles from any traditional hardware store so getting materials for DIY projects is rough. I had to order in the damn PVC pipe as it is, as no one had any 4"!

I finished all the other preassembly of my new TC today and am about to take a break and then go back to hand winding the last 3 inches. I am never winding by hand again. There WILL be a jig involved in the future. Also, I need a variac eventually.

Btw, in that video it looked like he didn't even have to use his finger to guide the wire in place to prevent gaps/overlaps, how was this done?

Inducktion

Wed May 02 2012, 03:44AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Yeah... I still want to make a Tesla Coil....but, the secondary winding just, ugh. xD

Sigurthr

Wed May 02 2012, 08:21AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

I hear ya Jared. The small TC secondary I bought off eBay wasn't sealed and the coilform shrank last night. The whole coil is a mess now. SO glad I put all the work in to my own DIY secondary. Which, btw, I finished tonight. No winding errors at all, but man it was painstaking. I think it took about 8 to 9 hours total.

I'm planning at least two more TCs in the coming months (micro SSTC and a MicroBRUTE DRSSTC) so I've got to make a jig for them.

Claude

Wed May 02 2012, 12:46PM

Registered Member #3379 Joined: Mon Nov 01 2010, 06:34AM
Location: Sydney, Australia
Posts: 24

I modified an old transformer bobin winding machine to accept larger coils. It has automatic wire feed which can be adjusted to suit the gauge of wire. Works great. Takes about 5 minutes to wind a 4"x 12" coil with 30 gauge.

Claude.

Tetris

Wed May 02 2012, 03:10PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

... I had a problem with the 30awg. Don't use 30awg. Even for my coil (smaller than yours) its too thin, use 26. its easier (i have no jig either) and it has lot less resistance. foot per ohm, its about 10 feet. Too much. I also had a problem with the crosses and stuff. It's annoying, and with 30awg, sometimes you wind a section perfectly, then 4 inches up realize that there is a gap. I went through the trouble of making 2 and a half (first time the wire broke half way through, i was literally crying because I did nothing but that for hours straight) secondaries with 30awg, and they are all defective. I am soon to be getting 26awg, and I think you should too to save you the trouble I went through,

Inducktion

Wed May 02 2012, 03:37PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Be great if anyone would be willing to offer Tesla coil winding services... :p

Of course you would supply your own wire, but it'd be an interesting idea. Maybe like $10 per secondary or something.

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