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Inductive Reactor - Slide-Choke

Updated:  July 17, 2005

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• Photo 1 - Finished.
• Photo 2 - Iron core assembly, in position, on the 1:1 scale drawing, with the white former to its left.
• Photo 3 - Winding the coil.
• Photos 4 & 5 - Ready for glyptal, paint, stain and shellac (all components were treated separately and then assembled).

The Procedure

1. Soak the welding rods in cold water and the flux will fall off after an hour or two.  Then use a green scrubbing pad to thoroughly clean each rod, while wearing rubber gloves

2. The rods were then stacked together, thoroughly cleaned, in a bundle, in the sink and were kept wet for 1.5 days, at which point they developed a light coat of rust (this is desirable and the point of this step), the scaling on the rods keeps them separate, electrically/magnetically speaking, the same processes are realized by the transformer manufacturers.

3. They were individually dried and inspected and using a scrap section of the form the core was going to occupy, I placed one rod at a time into it, stacking them and placing the threaded rod in the exact center and continuing until the form was full. 

4. This bundle was then laterally wrapped with a wide, clear tape and I cut a round steel disk to support the bottom of the rods, see photo 2. 

5. Then came the epoxy over the each end of the rod bundle, one end at a time, letting the epoxy run down into the bundle and harden, bottom end first as I pushed the rod (with the round plate) out a few inches, put epoxy over that end, pushed the plate and threaded rod back into position and then allowed it to harden.  Later, I turned it over, as it was clamped into one of my woodworking benches and poured epoxy over the top of the 450 rod bundle.  I'll soon find out how much noise it makes.  There are two 3" long ceramic spacers to support the start and end of the winding, to be connected with wire nuts at this point.

Specifications

• Iron Core = 450 welding rods.  About 25 lbs.  14" long, 1/8" o.d. with a 36", 1/4" threaded rod placed in the center of the iron bundle.  I've got to add that my computations of the number of rods required and the threaded rod, required to fill the former, was 450 rods.  As it turned out, I needed 452 rods, a very low percentage 'miss'.
• Former = 39.75" long, 3.25" o.d., 3.0625 i.d.  White PVC?
• Coil Wire = 650 to 700 feet of #12 solid THHN, 1/8" o.d.
• Coil Winding = tight-wound 20", 5 layers each separated by a layer of red duct tape.  I connected the two 500' spools of Essex wire (hate this company) by filing 0.25" of each end to a half circle, tinning them, slipping a number of pre-cut sections of shrink tube (two diameters) over one end, and then soldering them together.  The result was a solder joint with a lot of surface area that didn't appreciably deviate from the normal wire diameter.
• Inductance = 70.4mH to 10.2mH (with the bottom of the iron core one inch above the windings)
• Base = pine 17.5" o.d., 1" thick, Ebony Stained, Two Coats of Clear, De-Waxed Shellac.  Four rubber feet attached to bottom.
• Side Supports = Red Oak, Ebony Stained, Two Coats of Clear, De-Waxed Shellac.  There are two 1/4" - 20 nuts sunk into the bottom and one in the top of each support.  This is to allow replacement of the coil as I want to space-wind a 5 or 7 layer coil with 8# solid wire.  On this one, I just want the beginning of the coil to be at the bottom and the end at the top, hence the odd number of layers.  I'm expecting 70mH to limit the pole-pig to around 8 amps of draw, we'll see.
• Height = 41.5"
• Winding Resistance - 2.1 Ohms
• Fres - hmmmm, I don't quite know why but I'll measure it tonight.
• Calibration - there's a 3/8" diam. wooden rod about 20" long with 1" markings on it that align with the top of the 1/4" threaded rod.
• Here's the link to the wiring diagram for this component:  http://www.tesla-coil.com/Ballasting.htm   

Measurements

The Iron core (photo 2) is 14" long, 3.05" o.d. and the measurements begin with it centered within the 20" coil.  Below measurements are in milli-Henrys.  Measured with a calibrated BK Precision 875B LCR meter.

1. Centered - 70.4mH
2. Core Raised 1" - 69.9
3. Raised 2" - 68.8
4. 3" - 66.0
5. 4" - 61.8
6. 5" - 56.4
7. 6" - 51.0
8. 7" - 44.8
9. 8" - 39.2
10. 9" - 33.4
11. 10" - 28.3
12. 11" - 23.6
13. 12" - 19.7
14. 13" - 16.1
15. 14" - 13.5
16. 15" - 11.6
17. 16" - 10.6
18. 17" - 10.2mH, the bottom of the iron core is one inch above top of the 5 layer coil at this point.