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Re: Maxwell 37667 dies interestingly...thoughts?

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

Should have added a few more primary details:

Supply is a 14.7kV pole transformer.  Peak primary
current would have been around 250A.  Gap is async
rotary.  Estimated break rate:  About 400 bps.  Firing
seemed (sounded) consistent, though admittedly little
adjustment of the gap had been performed, so it may
have been a contributing factor in the Maxwell's
demise.  I'm not sure.

--- "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

> I took my Maxwell 37667 to a friend's place over the
> weekend to see if it would help get his new 24" coil
> to put out some sparks.  Despite early indications
> that things were too far from complete to run the
> thing, we got enough wire stripped quickly enough to
> do a temporary lash-up before daylight failed.
> Things kicked off with the destruction of two
> homemade
> rolled caps that he'd spent a bunch of time on.
> What
> a bummer (and boy did they look cool, too!).  I took
> a
> deep breath and offered to put the Maxwell on the
> cooker to see what would happen.  We were
> immediately
> gratified with 8- and 10-foot streamers as the break
> rate topped 400 bps.  Yikes!  We dropped a few
> different toploads on the thing and played around
> for
> a while.  In the end, the Maxwell probably had only
> two minutes of runtime spread over a ten-minute
> period.
> Then, Bad Thing #1 happened:  A streamer hit the
> wire
> between the Maxwell and the primary.  Due to the
> temporary nature of the wiring, the cap had been
> sitting relatively exposed a few feet from the base
> of
> the coil.  Doh!  A metal sawhorse was quickly placed
> over it.
> And finally, Bad Thing #2:  Shortly into the run
> immediately following placement of the sawhorse, a
> crack opened in the Maxwell, and the oil drained out
> rather quickly, leaving a nice puddle of Maxwell
> juice
> on the floor (VEERRRYY slippery stuff, I can now
> say!)
> What is quite interesting about all of this is that,
> due to the surpise of seeing the Maxwell croak, it
> took us a few seconds to kill the power.  In those
> few
> seconds, the coil continued to operate normally;
> there
> was no obvious dip in performance.  The contents of
> the Maxwell were quite warm, though not what I'd
> call
> "hot", and I neither saw nor smelled any sign of
> burning.  On top of that, measurement revealed that
> the capacitance was still 0.03uF, and no DC
> resistance
> would register on the DMM.
> So the mode of failure here is a little unclear to
> me.
>  Did thermal expansion of the contents simply pop
> the
> case, or was there most likely some kind of arcing
> fault, perhaps initiated or encouraged by the strike
> in the prior run?
> As the Maxwell's guts seemed in remarkable shape, my
> friend is going to try running them in a bucket of
> mineral oil and see what happens.  I'll report back
> with the results.  If they aren't serviceable, then
> perhaps we'll pry them apart even more and see what
> we
> find.  They were just too pretty not to get a second
> chance :-)
> Any other thoughts on "Why Maxwells Fail"?  I never
> even felt the thing get warm in my little coil
> running
> at 120 bps.
> Regards,
> Aaron, N7OE