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Re: [TCML] Pig Ballasting...



Travis,

If you could get your hands on an scrapped out decent sized
transformer, say like 10 kVA, and wind your own windings
on it, this would tend to minimize the eddy current heating,
as transformer cores are specifically designed to minimize
this.

I ended up getting the core from a scrapped out x-ray
transformer to build mine. This core was is two "C's"
and I had to install some no-ferrous spacers between the
two "C" halves to get the desired current control. With
no spacing, there was not enough current flow, even into
dead short. With too much spacing, the current would
go too high, so I placed an AC clamp-on ammeter on
it and kept adjusting the spacing until I got the desired
current flow into a dead short. Seems like I ended up
with about 3/8" spacing to get the current flow that I
wanted (around 100 amps for me ;^).  I wound each
"leg" of one of the "C's" with about 110 turns of #6
THNN copper cable and ran them in parallel. IIRC,
the core cross section is about 11 square inches and
this makes for a very robust ballast that's never gotten
even noticably warmer than ambient temperature through
all of my abuse ;^)

Maybe this will give you some ideas,
David

----- Original Message ----- From: "Travis Tabbal" <travis@xxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, October 27, 2012 9:50 AM
Subject: Re: [TCML] Pig Ballasting...


Thanks for the info Joe. I was wondering what you got for current when
running as an air core.? I saw one post last night where someone just used
the spool of wire as it came from Home Depot and it didn't get too hot. I
seem to recall the current being about 20 amps. I'm tempted to try it just
to see what it does.
On Oct 27, 2012 7:53 AM, "Joe Mastroianni" <joe@xxxxxxxxxxxxxx> wrote:


I did what you are suggesting, only I used 500' of 10GA.   I made a spool
out of 2" PVC with some flat polycarbonate scraps glued on the ends (but
not blocking the interior hole of the PVC) to hold on the wire. The spool
is about 18" long. Took quite a bit of muscle to wind.

I experimented with different configurations for the core. I had a couple
8' rods of aluminum and steel that I cut up into 2" sections.  Generally
speaking the forces want to pull the rods into the core, not visa versa.
 If you do the math you see it doesn't matter which way the current is
flowing in the solenoid, so it doesn't matter that it's AC, then, either.

The real issue you face is heating of the core materials.  My pig is only
rated at 5KVA so I rarely pushed it above 10.  And in any case at 6kVA I
was getting ground strikes so I didn't feel the need for much more. I was
measuring the input V and I to the variac, as well as the output, and
shoving things into and out of the ballast core to get reasonable levels.
But those interior rods got really hot, probably because I just threw them
in there, but also probably because the eddies in some of the materials
were severe.

And the core would stay hot for a long time.  I never melted through the
PVC, but I was close.   I'm not sure the best way to cool it down as I
switched to DR coils and didn't experiment much more with that.

Cheers,
Joe


On Oct 26, 2012, at 10:27 AM, Travis Tabbal wrote:

> I've seen a number of options in the archive. I was just wanting to get
> input on what I wanted to try to make sure I'm not off the deep end
> somewhere before I mess with it. Piggy is 14.4kV 10kVA.
>
> I was thinking of getting a 500' spool of AWG12 THHN wire from Home > Depot
> or similar and winding it around a 2" PVC or similar tube, about 1.5ft
> winding length. Then getting some ferrous wire from there as well,
perhaps
> something like the little yard flags or something from the fencing
> department for the core. I'd pot the core material inside a smaller > tube,
> even just as a mandrel, with epoxy or similar (Bondo?). With a threaded
rod
> at the top of the potting for adjustment. Then just build a frame to > hold
> it together while in operation, seems like the cycling of the magnetic
> field from the 60Hz AC might want to push the core out otherwise?

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