Re: [TCML] Coil Died

[David Thomson <tcbuilder@xxxxxxxxxxxxxxxxxxxxxxxx>]

The moment your primary broke, the transformer received a high current
spike from the suddenly changed secondary to primary step down ratio.  The
energy that one cycle of the spark gap placed into the secondary was
significantly increased on the return stroke.  The problem could be in the
transformer.

Oddly enough, I have had this happen in the past, and when I let the
transformer set on a shelf for a few years, it would perform like new when
placed back into service.  It is as though it self-healed over time.  This
makes me think the high current on the back stroke may have magnetized the
core in such a way as to prevent the transformer from working properly.

Do you have a compass or some other way to check for permanent magnetism in
the core?  I'm not even sure that would work since the magnetic loop would
be closed.

I'll have to look for the info, but someone patented a process for
increasing the amount of power in a motor by a factor of four without
increasing the input energy.  This is done by creating a magnetic switch in
the transformer core that redirects the magnetism in such a way as to
require one fourth of the power.  (All the new power drills use this
technology.)  This process may inadvertently occur in regular transformers
when used with high voltage applications.  This is just one of my wacky
ideas, but if it is a magnetism problem, perhaps the application of strong
neodymium magnets temporarily applied (with the circuit off) in just the
right way could reset the magnetism in the core?

I have not immediately recovered from this situation in the past without
starting a new coil from scratch.  If you have to, just put the whole
project on the shelf for an extended period of time and see if it heals
over time.

Also, double check your secondary with a magnifying glass.  Not all
secondary failures are obvious.  The fact that your doorknobs give you a
little bit better service just may be in the capacitance value and a
slightly more favorable reactance.  The main problem is either in the
transformer or the secondary.  And one more thing, the 3/4" PVC core may be
acting as an electrophorus.  If a permanent E field has built up in the
secondary core it will increase the reactance considerably.  Time will
eventually reset the electrophorus, too.

Dave


On Thu, Oct 10, 2013 at 10:14 AM, Tim Flood <tfloodrr@xxxxxxxxx> wrote:

> Thanks to all for your replies.
>
> Dave, the thickness of the coil form is 3/4".
>
> I disassembled the secondary coil to inspect the interior and found no
> signs of carbon tracking. Also ran a rag through the inside just in case
> there was any contamination. There did not appear to be any damage to the
> secondary winding.
>
> I did remove the MMC string and re installed the door knob caps. As soon as
> I began turning up the variac little sparks developed along the length of
> the sec. winding. This sparking stopped as the voltage increased. The TC
> then performed a little better with the door knobs back in - then quit as
> far as producing arcs from the toroid.
>
> Another bit of information. When the discharges from the top load quit, the
> firing of the static spark gaps seemed to drop in voltage as though the
> variac had been decreased by 50%. I also received a very mild shock from
> the variac body.
>
> I did not change anything that would effect the coupling, but I will try
> some adjustments. This coil has always been a good performer. The
> performance has been slowly dropping off over the past year, though.
> Thought I had the reason why when I found the cracked primary ribbon. Now
> it acts like a completely different coil.
>
> Could one of the two paralleled NSTs be contributing to the problem? I'm
> about ready to start over and build a completely new one, but I need this
> one in the near future.
>
> Please keep the advice coming.
>
> Thank you,
>
> Tim Flood
>
>
>
>
>
> On Wed, Oct 9, 2013 at 8:39 PM, David Thomson <
> tcbuilder@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Wed, Oct 9, 2013 at 3:57 PM, Tim Flood <tfloodrr@xxxxxxxxx> wrote:
> >
> > > Thanks. One thing I maybe should have mentioned is that PVC tube wall
> > > thickness is about 3/4". But I will disassemble and take a look tonight
> > for
> > > any signs of arcing inside.
> > >
> > Are you saying you have 3/4" PVC between the primary and secondary?  Or
> is
> > this the thickness of the secondary coil form?
> >
> > Dave Thomson
> > _______________________________________________
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