Ballast choke questions

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Original poster: "J. B. Weazle McCreath by way of Terry Fritz <twftesla-at-uswest-dot-net>" <weazle-at-hurontel.on.ca>


Hello Coilers,

I've spent the last two evenings disassembling a large transformer
that I acquired with the intent to rewind it as a ballast choke to
use with a 5 KVA pole pig I'm getting.

The stack of E and I laminations measures 3.5 inches thick, with
external dimentions of 7 inches by 7.75 inches.  The center most
leg, or the middle of the E measures 3.5 inches by 2.25 inches.
The two "windows" measure 5 inches by 1.5 inches.

Now for the questions to you transformer and choke experts:

1) How much power should a core of that size be capable of?

2) When re-assembling the core, should the laminations be
   put back interleaved as originally found, or should all
   of the E's be put together facing the same way?

3) If all E's are aligned, should there be an insulator put
   into the gap between the E's and the I's?

4) I'm going to put multiple taps on the choke windings for
   selecting different currents.  Should the first 79 turns
   as per the table below go nearest to the core, or on the
   outside of the windings?

Quoted from a post by Bert Hickman:

>The example below assumes a 250 turn ballast
>and a 10:1 current range in 10% increments.
>
>  
>           Multiplying   Turns
>            Factor:      at Tap
>
>   Nmax      1.00        250    Total number of turns (Max. L)
>   N(90%)    0.95        237
>   N(80%)    0.89        224
>   N(70%)    0.84        209
>   N(60%)    0.77        194 
>   N(50%)    0.71        177
>   N(40%)    0.63        158
>   N(30%)    0.55        137
>   N(20%)    0.45        112 
>   N(10%)    0.32         79
>

Any and all comments are welcomed.  I want to do this once and do
it right the first time.  Thanks in advance.
 

73, Weazle, VE3EAR/VE3WZL

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  www.hurontel.on.ca/~weazle