Recreating an original coil

A project log for Universal Coil winding Machine

A lost art, that few can still use, and guard viciously as a company secret.

brettBrett 07/17/2022 at 21:140 Comments

So, I have a BEHA gas lamp tester that uses a simple flyback feedback style to generate roughly 12kv to test gas lamps. It has nothing wrong with it but for science I am going to strip it down and other coils to learn how to recreate them.

First I need to find out the type of wire used. It was potted but I managed to strip the epoxy with a heat gun due to the coil being impregned with paraffin prior potting which allowed it to peel off without much damage.

1. OD of wire is 0.07mm
2. Lit it on fire to strip the cotton/silk and determine whether it is solid, or litz. It was solid, 0.05mm so roughly 41 to 40 AWG cotton, nylon or silk severed enamel coated wire.

3. Next I observe the top of the coil, it has a bike spoke pattern which tells me it is an even number of bends as per the coil winding pdf listed in the files I have included.

4. Now this is where it gets hairy, 15 spokes raised from center to edge, 15 sunk from center to edge, 30... to check if my math is correct I take the wire dia 0.07mm x 30 = 2.1mm now to check the height of the coil against the math. It measured 4.17mm so my assumptions were incorrect. 0.07mm x 60 = 4.2mm is the correct math, however it does not resemble 60 turns for a coil. It looks more like a 1,000 turn because I have wound similar ones, so what is missing?

5. The thing here is, to make ONE full layer which is the height of the wire dia x 2, it needs to go around 360 more than ONE revolution. The circumference of the bobbin, width of coil, n total bends, phasing/spacing and wire diameter determines the total amount of 360* revolutions that are required to create one full layer, and the amount of times it did this will be 1 times the total height of the coil in this case it was 60, and assume it took 40 revolutions to create 1 full layer so 60 divided by half (because it overlaps it created 2x the wire dia as a single layer) now we are left with 30x40=1,200 turns.

That seems a lot more accurate to create 12,000 volts. (2x9v batteries = 18v, subtract losses, say 70% efficiency which is 12.6v assuming fresh batteries. 12.6v x 1,000 turns... BOOM 12,000 volts. Math is your friend.

6. So, how do we get that total 360* revolutions number to know exactly what to input into the turn amount? First we find C, for circumference. This is the OD of the coil bobbin. Let's say its 16mm So where C is circumference, we put 16. Example C*3.14= is 16*3.14=50.24mm total surface circumference.

With that number, now we need the coils width, and the wire diameter/spacing. I have one that's 3.25mm wide now we divide that against the wire diameter. Say the wire dia is 0.07mm... 3.25 divide 0.07mm equals 46.42 total revolutions to create one full layer that is wire diameter * 2 (due to overlap)

So, lets back up a bit to the coil in question I am trying to recreate.6.37mm wide divided by 0.07mm OD of wire =91 now 91*30=2,730 total turns. Whups, probably more like 20kv anyways it is not as wide as my 1k coils on a 16mm bobbin, however it is not a "pi" wind, its either progressive, or retrogressive and it un-evenly moves a little to the left or right gradually building layers interlocking them increasing the width all while retaining the high Q low, Capitance quality. I have mostly been focusing on "pi" style anyways. That's y'alls lesson for today, again if anyone thinks they can help with coding to flesh out the features let me know.