Re: Why is the coil being weird???? (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sun, 11 Nov 2007 22:06:25 -0600
From: David Dean <deano@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Why is the coil being weird???? (fwd)

Hi Jay

What kind of bolts? If they are iron or steel The thermal "resistance" as well 
as the electrical resistance will be quite a bit higher than brass/bronze or 
copper. When I first started with a polemount distribution transformer I had 
a single static gap made of brass rods 3/4 inch in diameter. It took all the 
air my shop compressor could deliver to quench, or more to the point, to blow 
out the gap. The compressor is 5HP two stage and rated 17 CFM free air and 14 
CFM at 90 PSI.  The flaming arc driven out by the air blast would extend 5 or 
6 inches above the gap. Still I had to keep run times short as the compressor 
would need to catch up after only a minute or so. 

Oil burner ignition transformers are usually rated something like 23 mA, so if 
yours are typical then five in parallel would be 115 mA which could deliver 
sufficient power to heat those bolts rather quickly (assuming steel) and if 
they have any markings on the heads, or if you are using the other ends where 
the threads start, the high points will keep the arc in the same place all 
the time. This can make one or more hot spots which may even become 
incandescent.  Heat sinks on the outside of the tube would not help much in 
that case.  

Most folks using a static gap at higher power levels recommend a multi section 
gap like the RQ style which spreads the spark over several electrodes and 
offers a large surface area for heat dissipation. Copper pipe section or 
copper pipe couplings are usually the preferred material.

It could be a failure in the capacitors, either shorting out or heating up and 
changing value which throws the tuning off, but my experience with homemade 
capacitors is that once they start to fail they just don't come back. I had 
some homemade rolled polyethylene and aluminum flashing under oil and they 
died hard and fast.

Another possibility might be something in the primary circuit is getting hot 
and "spoiling the Q" or increasing the resistance in the circuit. Causes for 
that would be using too small gauge hookup wire, cheesy alligator clips, 
using iron wire to wind the primary, etc.

The symptoms you describe however sound most like the spark gap is heating up 
and power arcing rather than quenching.  Only a better gap or a significant 
reduction in power will help. You might try just one OBIT or maybe two and 
see if the coil runs better/ lasts longer. 

later
deano
On Sunday 11 November 2007 08:21:56 pm you wrote:
> ---------- Forwarded message ----------
> Date: Mon, 12 Nov 2007 01:58:31 +0000
> From: jhowson4@xxxxxxxxxxx
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Why is the coil being weird???? (fwd)
>
> Currently the spark gap is 2 bolts in a tube that is connected to blowing
> end of a shopvac.  There is considerable airflow through the gap.  Maybe I
> should put heat sinks on the exterior of the tube.
>
> many thanks,
> Jay Howson
>
>
>  -------------- Original message ----------------------
> From: "Tesla list" <tesla@xxxxxxxxxx>
>
> > ---------- Forwarded message ----------
> > Date: Thu, 08 Nov 2007 13:11:39 -0500
> > From: futuret@xxxxxxx
> > To: tesla@xxxxxxxxxx
> > Subject: Re: Why is the coil being weird???? (fwd)
> >
> >
> > Jay,
> >
> >
> >
> > The spark gap is mostly overheating during operation.
> >
> > Try letting a fan blow across the gap to keep it cool.
> >
> > It should help a lot.? A better spark gap may be helpful
> >
> > depending on the present design.
> >
> >
> >
> > John
> >
> >
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: Tesla list <tesla@xxxxxxxxxx>
> > To: tesla@xxxxxxxxxx
> > Sent: Thu, 8 Nov 2007 9:46 am
> > Subject: Why is the coil being weird???? (fwd)
> >
> >
> >
> >
> > ---------- Forwarded message ----------
> > Date: Wed, 07 Nov 2007 21:49:41 +0000
> > From: jhowson4@xxxxxxxxxxx
> > To: tesla@xxxxxxxxxx
> > Subject: Why is the coil being weird????
> >
> > I have been tinkering with my coil for a while now and it has been acting
> > weird since the day I built it.  but it is just starting to get on my
> > nerves.
> >
> > So basically
> > When I run my coil at first if is good.  producing 30" sparks lots of
> > noise etc.
> >
> > But after about 5-6 seconds it just craps out.  The spark gap stops
> > making the normal loud spark gap sounds and it starts to make a really
> > quick softer sound. Like the one the tv makes when there is no channel
> > and just static.  At the same time the sparks length drops to about 4".
> > I turn it off.  let it chill for like 30 seconds and then it does the
> > same thing.   If I turn it off and don't let it chill it just does it
> > quicker. Very annoying.
> > I am currently using 5 obits in parallel and 2    .005uf home made
> > capacitors. The spark gap is 2 bolts less than 1/4" apart in a tube that
> > is connected to the blowing end of a vacuum.  The frequency is about
> > 600kHz.
> > Any ideas and  help will be great.
> >
> > Many thanks,
> > Jay Howson
> >
> >
> >
> >
> > ________________________________________________________________________
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