Re: Ballast choke questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> 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?
>
> SNIPPERZZ>>>

>
> 73, Weazle, VE3EAR/VE3WZL
>

Hi Weazle...

Looks like you have a decient core for about 17 - 20 amps max ....(
depending on the wire size you plan to use)
any much more than that then you start running into problems with saturation.

if you pulled all of the leaves apart, the best bet is to spray them all
with a varnish ( both sides) to replace
any lost insulative film. I would place all of the "E" leaves in the same
position for the rebuilding process,
makes putting the core back on easier.

by putting an insulator between the E & I cores  introduces an "air gap"
this gap will increase the reluctance
of the core assy. thus increasing the ability to produce more amp draw to
the pig before saturation occurs ( but
it only works to a certian degree.  3/8" - 1/2" will increase amp draw
capacities by about 30 - 40% compared to
a close fit E I combination.

 the taps are on the outer portion of the windings.

try to use a #8 solid Cu wire THHN insulation 90 degree+ Centigrade rating

If you use the I section without an airgap you will probably see about 5
amps limit an air gap will produce
about 17A max. ( varies upon distance) raising the core off the center leg
a bit will go to about 20 or so amps.

create a bobin to wind the core on, make sure it fits a little loose on the
core leg, make the bobin sturdy! :)
wind the wire TIGHTLY on the bobin ( what i do is create a "sampleleg" from
wood about 1/8" larger than the core
leg. Then I place some G10 ( 1/16") on the sample leg and start winding.
after winding remove the wooden sample
leg and place on core center leg)


I have a core similar to what you have and it was wound with THHN solid Cu
#10 wire for 200 turns. I didnt tap
mine but used another method to increase amp flow. I raised the core up a
bit off of the center leg by about
3/4" ( no I section was used)

Something to consider..  if you use a variac to control voltage, there
really isnt a need for variable
inductance. The varying of the voltage will give you a varied curent flow (
semi-sorta-kinda)  btw at full
voltage you dont need to go any further than max current flow of the
systems rating ;)


Scot D