Re: RE- Re: Bombarder xfmr

Subject:       Re: RE- Re: Bombarder xfmr
      Date:    Tue, 10 Jun 1997 04:31:52 GMT
      From:    jim.fosse-at-bjt-dot-net (Jim Fosse)
        To:    Tesla List <tesla-at-pupman-dot-com>
       CC:    robert.michaels-at-online.sme-dot-org
References:   1

>       Date:  Fri, 06 Jun 1997 10:28:00 GMT
>       From:  robert.michaels-at-online.sme-dot-org (Robert Michaels)
>Organization: Society of Manufacturing Engineers
>         To:  tesla-at-pupman-dot-com
>T>For mild over power use: if it doesn't smell, it's OK. For longer term
>T>use: if you can hold your hand on it for 3 seconds (power off please;)
>T>it's ok. (engineers, unless you have specific info on THIS xformer, or
>T>a better rule of thumb, keep the flames to yourself)

>        I'm not here to flame -- but maybe warm up the outer edges
>        a little ( but I won't make a stink & it's nothing you couldn't
>        hold your hand on for 3 seconds):

I don't know about that, it took me 3 days to come up with a non-vapid
rebuttal:)      I can't: rebuttal that is.  Vapid, I don't need much
help on;)

>        I fear the smell/hand test my lead some astray, into
>        blown-transformer never-never land.
>        In Tesla work, over-driving a transformer, or even not
>        over-driving it, can cause over-voltage conditions.

Agreed. Neon's have a very limited voltage standoff.

Last year, I contacted MagnaCraft, the holder/owner of
Jefferson-Electric, about the design of my 15kV 60mA Jefferson neon.
After talking to "tech-support (? an engineer?)" for about 15 minutes,
I developed the opinion that, Neon's were not so much designed as,
but, arrived at - they have just enough insulation to hold up against
the very low duty cycle "full voltage" transients during neon-sign
startup.  The tar is used mainly as a water-proffing agent.  To
paraphrase Richard Hull: "they are doomed to failure in TC use" (IIRC)

>  Such
>        can cause  =brief=  (sometimes very brief) internal arcing
>        which in turn can cause an internal open circuit in a trice
>        (which is also very brief).

which would cause (in a thrice) the 3/16" pit 3/4 of the way down my
"first" blown neon's secondary. (as I found out after I depotted it).

I don't believe that the neon's max current could have caused this
sized hole because it just doesn't have enough energy to blow a clean
hole in a copper/fish paper/tar composite;)  But, the short circuit
current from my ~14nF (aka14,000 micky-mikes;) rolled cap (or any low
Esr/Esl cap) WOULD blow a hole in the neon's secondary.

>        There would never be any
>        opportunity for any touchy-feely (or smelly) nor either
>        any external warming to touchy-feel.  (You  did expressly
>        state "power" overload in your post, but in Tesla work,
>        power can translate to voltage in untoward ways.)

You are correct here. I made several unspoken assumptions about the
design of this transformer, the main one (based on it's 250mA output
current); this is a bombardier xformer, not a neon!

Oops, it may have been designed {sic} with the same voltage
constraints that a neon was/is/may-have-been. That is: 30kV for
several milliseconds whilst the gasses ionize and then ~1kV (???).
>        Only a  =current=  overload is apt to generate any palpable
>        heat -- and then only after that heat has had a chance to
>        overcome the thermal inertia of the transformer's mass.  In
>        the pole-pig mass-class, by the time a transformer fails the 3-
>        second touchy-feely externally, it may be about right for
>        cooking french-fries internally.

Absolutely. Big grin, I'm visualizing heating my Westinghouse 10+ pig
to "hot-to-the touch" on the outside with a transient over-power
condition. Or for that matter, heating a neon to "hot-to-the touch"
with a short power transient.
>                                - - - - - - - -
>        I'm not saying your basic premise is wrong, only a little
>        oversimplified -- and apt to be mis-applied by some readers.
>        Hey -- I'm the guy who unabashedly advocates wholesale over-
>        volting (but not over =powering=) military-spec. transformers,
>        so we are both brothers of the Cause.
Yes it was.  I had left out all my assumptions.  I stated a rule of
thumb without stating ALL the assumptions that go along with it.

        So Robert M.,  What rule of thumb do you suggest for this