Ballasting and a small problem

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

Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sundog-at-timeship-dot-net>

 Hi All,

 Got my 240v drop done last night, and of course, wired my pig up
and let 'er rip on a jacob's ladder so I could get my ballasting
set properly.

 The breaker running it is a 240v60A unit (1 in the breakerbox out
back and one in the garage drop-box.)  Switching the pig is via a 3
phase Furnas contactor (550v-at-350A Yeah!!!)  Ballast is a couple of
MOTs that I scrounged from a set of MV ovens.

 My target power levels are 4, 7, and 10 kva.  That means I'll be
running 16A, 30, and ~42A.  Both of my MOTs in series with 1 240v
leg gives me the required inductance for 30A operation, but the
problem I ran into is that in about 10 sec of operation in a
Jacob's Ladder one of the MOT's caught fire with a sharp *POOF!*.
There was on warning to it. no burning smell or smoke till *after*
it erupted.  The unit still works, but it's not too pretty and I
don't trust it.

 In the spirit of "Hmm..wonder if this will work...", I grabbed a
scrap 12/30 NST core I had lying in the corner, hacksawed out the
shunts (part of the core), and wrapped a layer of cardboard on it,
then started winding 12ga THHN wire.  I forget the number of turns
on it (kept getting interrupted and I'm winding it by hand), but in
series with the good mot it chokes the current down to ~45A (from
75A with just the MOT itself).  THere's 3 layers of wire on it now,
and I have room for probably another 3 or 4 more.  (and still be
able to slide the core back together with some cardboard between
the wire and steel to prevent chafing and nicks in the insulation.

 Will that core saturate eventually when used as a choke?  Reading
about how variacs behave, I think it will.  The real problem I'm
having is just the *HEAT* the ballasts are creating.  I can throw a
few spools of wire in series with the 240 to bring it down (no
steel core, not as much heat).  But the MOTs simply get nuclear hot
after only 10 seconds of runtime.  About 1 total minute of runtime
(10 sec on, 20-30 sec off), and they're stinking to high heaven and
doing a good imitation of space heaters.  I will grudgingly wind my
own ballasts if I have to, but I'd rather not if I can help it.
Time consuming, but the payoff is I get *exactly* what I want.
Jumping to a forced 10kva from the 4 that I'm wanting isn't eactly
what I had in mind.

 An idea I remember seeing on the list (can't remember who put it
up), is to attach a lead to the MOT case and MOT HV windings, and
raise or lower them in a container of water (using water as the
resistor) to control the inductanceof the MOT.  I'll give it a
whirl (on a 120v line, just measureing the current draw of the MOT
as I raise and lower the cup remotely (ain't no way I'm grabbing a
glass of water at 2.5kv .5A!).  I think this will only be a
temporary solution to my ballasting problem, but it's worth a try.
What I'm looking for is a ballast that can handle the 16-40A
current for a few minutes or more (forced air cooling is acceptable
on it), but it's looking like a welder is my only answer for that,
and those are a bit difficult for me to come by.

 Ideas?  Suggestions? Thanks!
                                                        Shad


PS, this pig just *ROCKS!*  No more fear of the tranny dying!