# Re: Inductance Calculations for iron core

```to: Mike

We use approx 40-40 mHy series inductance with a gapped core.  We use 125
turns of #10 AWG -- remember with a pole pig your peak currents are going to
be close to 70-80 amps for short saturation durations so you need much
larger wire than you might imagine for a 30 amp circuit.  The additional
inductance is of course provided by the variac as a standard voltage
controller.  Without a variac in the circuit more inductance is required.

I will check a core for you tomorow for cross sectional area.  We use a
Nomex gap material for 0.120 inch gap on each side of the C core.  We also
run a 0.5 Ohm, 5 kVA resistor in series with the reactor to limit short
duration peaks to reasonable values.  Very tightly banded with stainless
steel strap --- don't use regular banding steel as it will act as a shorted
turn and get red hot fast.

Regards,

Dr.Resonance

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Monday, July 12, 1999 4:53 PM
Subject: Inductance Calculations for iron core

>Original Poster: "Coiler" <mycroft-at-access1-dot-net>
>
>Looking for some help with figuring out how to build my own current
limiting
>inductor for my pig. Please don't tell me "you can do it
>better/cheaper/etc.."
>I already know that (I currently use a Lincon 225A AC welder as my
limiter.)
>I'm just one of those "Build it yourself" type of guys :)
>
>What I am looking for is a guesstimate, or even the formulas to compute
>the inductance knowing the approximate cross section area. My plan is to
use
>a bunch of rebar tie wire I have here, cut to about 20" lengths, to fill
>a 2" PVC pipe. This would give me an open core with about a 1.6 square inch
>cross section.
>Estimated inductance per turn would be best, I'll probably use #10 THNN
wire
>for about 6 TPI. (roughly 110 turns end to end)
>
>The OD of the PVC is actually 2.4" if that helps.
>(and if someone could refresh me on the formula for reactance, I wouldn't
>complain
>either :) )
>Thanks!
>
>Michael Baumann
>Coiler, Homebrewer, Nerd. mycroft-at-access1-dot-net
>
>
>

```